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Python Tutorial 1 -

Python Tutorial 1

Python Tutorial & Video Lessons

Learn python in 7 hours! Python Lessons A complete course of learning to program in python from scratch

  1.   00:00  Introduction to the course of python lessons
  2.   00:45  Installing python, the first program
  3.   10:47  Variables
  4.   20:56  Data types in pytho
  5.   30:02  Conditional statements if, elif, else
  6.   39:03  Conditional statements 2
  7.   45:53  Conditional Operators Practice
  8.   56:44  while loop
  9.   1:12:37  for loop
  10.   1:21:23  A for loop, a loop within a loop
  11.   1:29:34  Lists, list data type
  12.   1:41:29  Lists, methods of the list data type
  13.   1:53:21  Tuples, tuple data type
  14.   2:08:42  Practice python, os module, walk function
  15.   2:21:16  def functions, definition, and call
  16.   2:30:07  def functions, parameters, and arguments
  17.   2:43:49  Functions variable number of arguments, *args parameter
  18.   2:56:28  Functions, variable scope
  19.   3:08:49  Functions and code structure
  20.   3:22:07  Dictionaries, data type dict
  21.   3:37:22  Dictionaries, dict methods
  22.   3:49:21  Reading and writing files
  23.   4:05:29  Sets, set data type
  24.   4:22:30  Strings escaped characters
  25.   4:30:17  Strings, str methods
  26.   4:43:13  f-string, string formatting
  27.   4:50:10  Exception handling, try, except
  28.   5:09:59  Context manager with as
  29.   5:16:19  Import modules, if __name__ == ‘__main__”
  30.   5:34:58  Dice game in python Tkinter
  31.   5:56:53  Decorators
  32.   6:10:36  List, dictionary, set generators
  33.   6:30:56  Generator expression
  34.   6:43:03  Generator function, the yield statement   
  35.   6:51:51  lambda function

Python Tutorial

Python lessons for beginners from scratch – a complete course for learning to program in Python. Learn the python programming language for free, basics from scratch, complete python learning lecture course. The course video covers all the main topics with examples and practice necessary for a junior python developer. At the end of the course, you will know all the basic python syntax and be free to write your own code!

Python is a popular programming language. Python can be used on a server to create web applications.

Python Variables

Python Variables

Variables

Variables are containers for storing data values.


Creating Variables

Python has no command for declaring a variable.

A variable is created the moment you first assign a value to it.

Example

x = 5
y = "John"
print(x)
print(y)

Try it Yourself »

Variables do not need to be declared with any particular type, and can even change type after they have been set.

Example

x = 4       # x is of type int
x = "Sally" # x is now of type str
print(x)

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Casting

If you want to specify the data type of a variable, this can be done with casting.

Example

x = str(3)    # x will be '3'
y = int(3)    # y will be 3
z = float(3)  # z will be 3.0

Try it Yourself »


Get the Type

You can get the data type of a variable with the type() function.

Example

x = 5
y = "John"
print(type(x))
print(type(y))

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You will learn more about data types and casting later in this tutorial.

Single or Double Quotes?

String variables can be declared either by using single or double quotes:

Example

x = "John"
# is the same as
x = 'John'

Try it Yourself »


Case-Sensitive

Variable names are case-sensitive.

Example

This will create two variables:

a = 4
A = "Sally"
#A will not overwrite a

Try it Yourself »

 
 

Python – Variable Names

Variable Names

A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume). Rules for Python variables:

  • A variable name must start with a letter or the underscore character
  • A variable name cannot start with a number
  • A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
  • Variable names are case-sensitive (age, Age and AGE are three different variables)

Example

Legal variable names:

myvar = "John"
my_var = "John"
_my_var = "John"
myVar = "John"
MYVAR = "John"
myvar2 = "John"

Try it Yourself »

Example

Illegal variable names:

2myvar = "John"
my-var = "John"
my var = "John"

Try it Yourself »

Remember that variable names are case-sensitive


Multi Words Variable Names

Variable names with more than one word can be difficult to read.

There are several techniques you can use to make them more readable:

Camel Case

Each word, except the first, starts with a capital letter:

myVariableName = "John"

Pascal Case

Each word starts with a capital letter:

MyVariableName = "John"

Snake Case

Each word is separated by an underscore character:

my_variable_name = "John"

Python Variables – Assign Multiple Values

Many Values to Multiple Variables

Python allows you to assign values to multiple variables in one line:

Example

x, y, z = "Orange""Banana""Cherry"
print(x)
print(y)
print(z)

Try it Yourself »

Note: Make sure the number of variables matches the number of values, or else you will get an error.


One Value to Multiple Variables

And you can assign the same value to multiple variables in one line:

Example

x, y, z = "Orange"
print(x)
print(y)
print(z)

Try it Yourself »


Unpack a Collection

If you have a collection of values in a list, tuple etc. Python allows you to extract the values into variables. This is called unpacking.

Example

Unpack a list:

fruits = ["apple""banana""cherry"]
x, y, z = fruits
print(x)
print(y)
print(z)

Try it Yourself »

Learn more about unpacking in our Unpack Tuples Chapter.

Python – Output Variables

Output Variables

The Python print() function is often used to output variables.

Example

x = "Python is awesome"
print(x)

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In the print() function, you output multiple variables, separated by a comma:

Example

x = "Python"
y = "is"
z = "awesome"
print(x, y, z)

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You can also use the + operator to output multiple variables:

Example

x = "Python"
y = "is"
z = "awesome"
print(x, y, z)

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Notice the space character after "Python " and "is ", without them the result would be “Pythonisawesome”.

For numbers, the + character works as a mathematical operator:

Example

x = 5
y = 10
print(x + y)

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In the print() function, when you try to combine a string and a number with the + operator, Python will give you an error:

Example

x = 5
y = "John"
print(x + y)

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The best way to output multiple variables in the print() function is to separate them with commas, which even support different data types:

Example

x = 5
y = "John"
print(x + y)

Try it Yourself »

Python –Global Variables

Global Variables

Variables that are created outside of a function (as in all of the examples above) are known as global variables.

Global variables can be used by everyone, both inside of functions and outside.

Example

Create a variable outside of a function, and use it inside the function

x = "awesome"

def myfunc():
print("Python is " + x)

myfunc()

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If you create a variable with the same name inside a function, this variable will be local, and can only be used inside the function. The global variable with the same name will remain as it was, global and with the original value.

Example

Create a variable inside a function, with the same name as the global variable

x = "awesome"

def myfunc():
x = "fantastic"
print("Python is " + x)

myfunc()

print("Python is " + x)

Try it Yourself »


 

The global Keyword

Normally, when you create a variable inside a function, that variable is local, and can only be used inside that function.

To create a global variable inside a function, you can use the global keyword.

Example

If you use the global keyword, the variable belongs to the global scope:

def myfunc():
global x
  x = "fantastic"


myfunc()

print("Python is " + x)

Try it Yourself »

Also, use the global keyword if you want to change a global variable inside a function.

Example

To change the value of a global variable inside a function, refer to the variable by using the global keyword:

x = "awesome"

def myfunc():
global x
  x = "fantastic"

myfunc()

print("Python is " + x)

Try it Yourself »

 
 

Python – Variable Exercises

Test Yourself With Exercises

Now you have learned a lot about variables, and how to use them in Python.

Are you ready for a test?

Try to insert the missing part to make the code work as expected:

Exercise:

Create a variable named carname and assign the value Volvo to it.

 = ""

Go to the Exercise section and test all of our Python Variable Exercises:

Python Variable Exercises

Python Strings

Python Strings

Strings

Strings in python are surrounded by either single quotation marks, or double quotation marks.

‘hello’ is the same as “hello”.

You can display a string literal with the print() function:

Example

print("Hello")
print('Hello')

Try it Yourself »


Assign String to a Variable

Assigning a string to a variable is done with the variable name followed by an equal sign and the string:

Example

a = "Hello"
print(a)

Try it Yourself »


Multiline Strings

You can assign a multiline string to a variable by using three quotes:

Example

You can use three double quotes:

a = """Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua."
""

print(a)

Try it Yourself »

Or three single quotes:

Example

a = '''Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua.'
''

print(a)

Try it Yourself »

Note: in the result, the line breaks are inserted at the same position as in the code.


 

Strings are Arrays

Like many other popular programming languages, strings in Python are arrays of bytes representing unicode characters.

However, Python does not have a character data type, a single character is simply a string with a length of 1.

Square brackets can be used to access elements of the string.

Example

Get the character at position 1 (remember that the first character has the position 0):

a = "Hello, World!"
print(a[1])

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Looping Through a String

Since strings are arrays, we can loop through the characters in a string, with a for loop.

Example

Loop through the letters in the word “banana”:

for in "banana":
  print(x)

Try it Yourself »

Learn more about For Loops in our Python For Loops chapter.


String Length

To get the length of a string, use the len() function.

Example

The len() function returns the length of a string:

a = "Hello, World!"
print(len(a))

Try it Yourself »


Check String

To check if a certain phrase or character is present in a string, we can use the keyword in.

Example

Check if “free” is present in the following text:

txt = "The best things in life are free!"
print("free" in txt)

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Use it in an if statement:

Example

Print only if “free” is present:

txt = "The best things in life are free!"
if "free" in txt:
  print("Yes, 'free' is present.")

Try it Yourself »

Learn more about If statements in our Python If…Else chapter.


Check if NOT

To check if a certain phrase or character is NOT present in a string, we can use the keyword not in.

Example

Check if “expensive” is NOT present in the following text:

txt = "The best things in life are free!"
print("expensive" not in txt)

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Use it in an if statement:

Example

print only if “expensive” is NOT present:

txt = "The best things in life are free!"
if "expensive" not in txt:
  print("No, 'expensive' is NOT present.")

Try it Yourself »

Python – Slicing Strings

Slicing

You can return a range of characters by using the slice syntax.

Specify the start index and the end index, separated by a colon, to return a part of the string.

Example

Get the characters from position 2 to position 5 (not included):

b = "Hello, World!"
print(b[2:5])

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Note: The first character has index 0.


Slice From the Start

By leaving out the start index, the range will start at the first character:

Example

Get the characters from the start to position 5 (not included):

b = "Hello, World!"
print(b[:5])

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Slice To the End

By leaving out the end index, the range will go to the end:

Example

Get the characters from position 2, and all the way to the end:

b = "Hello, World!"
print(b[2:])

Try it Yourself »


Negative Indexing

Use negative indexes to start the slice from the end of the string:

Example

Get the characters:

From: “o” in “World!” (position -5)

To, but not included: “d” in “World!” (position -2):

b = "Hello, World!"
print(b[-5:-2])

Try it Yourself »

Python – Modify Strings

Python has a set of built-in methods that you can use on strings.


Upper Case

Example

The upper() method returns the string in upper case:

a = "Hello, World!"
print(a.upper())

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Lower Case

Example

The lower() method returns the string in lower case:

a = "Hello, World!"
print(a.lower())

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Remove Whitespace

Whitespace is the space before and/or after the actual text, and very often you want to remove this space.

Example

The strip() method removes any whitespace from the beginning or the end:

a = " Hello, World! "
print(a.strip()) # returns "Hello, World!"

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Replace String

Example

The replace() method replaces a string with another string:

a = "Hello, World!"
print(a.replace("H""J"))

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Split String

The split() method returns a list where the text between the specified separator becomes the list items.

Example

The split() method splits the string into substrings if it finds instances of the separator:

a = "Hello, World!"
print(a.split(",")) # returns ['Hello', ' World!']

Try it Yourself »

Learn more about Lists in our Python Lists chapter.


String Methods

Learn more about String Methods with our String Methods Reference

Python – String Concatenation

String Concatenation

To concatenate, or combine, two strings you can use the + operator.

Example

Merge variable a with variable b into variable c:

a = "Hello"
b = "World"
c = a + b
print(c)

Try it Yourself »

Example

To add a space between them, add a " ":

a = "Hello"
b = "World"
c = a + " " + b
print(c)

Try it Yourself »

Python – Format – Strings

String Format

As we learned in the Python Variables chapter, we cannot combine strings and numbers like this:

Example

age = 36
txt = "My name is John, I am " + age
print(txt)

Try it Yourself »

But we can combine strings and numbers by using the format() method!

The format() method takes the passed arguments, formats them, and places them in the string where the placeholders {} are:

Example

Use the format() method to insert numbers into strings:

age = 36
txt = "My name is John, and I am {}"
print(txt.format(age))

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The format() method takes unlimited number of arguments, and are placed into the respective placeholders:

Example

quantity = 3
itemno = 567
price = 49.95
myorder = "I want {} pieces of item {} for {} dollars."
print(myorder.format(quantity, itemno, price))

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You can use index numbers {0} to be sure the arguments are placed in the correct placeholders:

Example

quantity = 3
itemno = 567
price = 49.95
myorder = "I want to pay {2} dollars for {0} pieces of item {1}."
print(myorder.format(quantity, itemno, price))

Try it Yourself »


Learn more about String Formatting in our String Formatting chapter.

Python – Format – Strings

Escape Character

To insert characters that are illegal in a string, use an escape character.

An escape character is a backslash \ followed by the character you want to insert.

An example of an illegal character is a double quote inside a string that is surrounded by double quotes:

Example

You will get an error if you use double quotes inside a string that is surrounded by double quotes:

txt = "We are the so-called "Vikings" from the north."

Try it Yourself »

To fix this problem, use the escape character \":

Example

The escape character allows you to use double quotes when you normally would not be allowed:

txt = "We are the so-called \"Vikings\" from the north."

Try it Yourself »


Escape Characters

Other escape characters used in Python:

CodeResultTry it
\’Single QuoteTry it »
\\BackslashTry it »
\nNew LineTry it »
\rCarriage ReturnTry it »
\tTabTry it »
\bBackspaceTry it »
\fForm Feed 
\oooOctal valueTry it »
\xhhHex valueTry it »

Python – String Methods

String Methods

Python has a set of built-in methods that you can use on strings.

Note: All string methods returns new values. They do not change the original string.

MethodDescription
capitalize()Converts the first character to upper case
casefold()Converts string into lower case
center()Returns a centered string
count()Returns the number of times a specified value occurs in a string
encode()Returns an encoded version of the string
endswith()Returns true if the string ends with the specified value
expandtabs()Sets the tab size of the string
find()Searches the string for a specified value and returns the position of where it was found
format()Formats specified values in a string
format_map()Formats specified values in a string
index()Searches the string for a specified value and returns the position of where it was found
isalnum()Returns True if all characters in the string are alphanumeric
isalpha()Returns True if all characters in the string are in the alphabet
isdecimal()Returns True if all characters in the string are decimals
isdigit()Returns True if all characters in the string are digits
isidentifier()Returns True if the string is an identifier
islower()Returns True if all characters in the string are lower case
isnumeric()Returns True if all characters in the string are numeric
isprintable()Returns True if all characters in the string are printable
isspace()Returns True if all characters in the string are whitespaces
istitle()Returns True if the string follows the rules of a title
isupper()Returns True if all characters in the string are upper case
join()Joins the elements of an iterable to the end of the string
ljust()Returns a left justified version of the string
lower()Converts a string into lower case
lstrip()Returns a left trim version of the string
maketrans()Returns a translation table to be used in translations
partition()Returns a tuple where the string is parted into three parts
replace()Returns a string where a specified value is replaced with a specified value
rfind()Searches the string for a specified value and returns the last position of where it was found
rindex()Searches the string for a specified value and returns the last position of where it was found
rjust()Returns a right justified version of the string
rpartition()Returns a tuple where the string is parted into three parts
rsplit()Splits the string at the specified separator, and returns a list
rstrip()Returns a right trim version of the string
split()Splits the string at the specified separator, and returns a list
splitlines()Splits the string at line breaks and returns a list
startswith()Returns true if the string starts with the specified value
strip()Returns a trimmed version of the string
swapcase()Swaps cases, lower case becomes upper case and vice versa
title()Converts the first character of each word to upper case
translate()Returns a translated string
upper()Converts a string into upper case
zfill()Fills the string with a specified number of 0 values at the beginning

Python – String Exercises

String Methods

Python has a set of built-in methods that you can use on strings.

Note: All string methods returns new values. They do not change the original string.

MethodDescription
capitalize()Converts the first character to upper case
casefold()Converts string into lower case
center()Returns a centered string
count()Returns the number of times a specified value occurs in a string
encode()Returns an encoded version of the string
endswith()Returns true if the string ends with the specified value
expandtabs()Sets the tab size of the string
find()Searches the string for a specified value and returns the position of where it was found
format()Formats specified values in a string
format_map()Formats specified values in a string
index()Searches the string for a specified value and returns the position of where it was found
isalnum()Returns True if all characters in the string are alphanumeric
isalpha()Returns True if all characters in the string are in the alphabet
isdecimal()Returns True if all characters in the string are decimals
isdigit()Returns True if all characters in the string are digits
isidentifier()Returns True if the string is an identifier
islower()Returns True if all characters in the string are lower case
isnumeric()Returns True if all characters in the string are numeric
isprintable()Returns True if all characters in the string are printable
isspace()Returns True if all characters in the string are whitespaces
istitle()Returns True if the string follows the rules of a title
isupper()Returns True if all characters in the string are upper case
join()Joins the elements of an iterable to the end of the string
ljust()Returns a left justified version of the string
lower()Converts a string into lower case
lstrip()Returns a left trim version of the string
maketrans()Returns a translation table to be used in translations
partition()Returns a tuple where the string is parted into three parts
replace()Returns a string where a specified value is replaced with a specified value
rfind()Searches the string for a specified value and returns the last position of where it was found
rindex()Searches the string for a specified value and returns the last position of where it was found
rjust()Returns a right justified version of the string
rpartition()Returns a tuple where the string is parted into three parts
rsplit()Splits the string at the specified separator, and returns a list
rstrip()Returns a right trim version of the string
split()Splits the string at the specified separator, and returns a list
splitlines()Splits the string at line breaks and returns a list
startswith()Returns true if the string starts with the specified value
strip()Returns a trimmed version of the string
swapcase()Swaps cases, lower case becomes upper case and vice versa
title()Converts the first character of each word to upper case
translate()Returns a translated string
upper()Converts a string into upper case
zfill()Fills the string with a specified number of 0 values at the beginning

Python Lists

Python Lists

mylist = ["apple""banana""cherry"]

List

Lists are used to store multiple items in a single variable.

Lists are one of 4 built-in data types in Python used to store collections of data, the other 3 are TupleSet, and Dictionary, all with different qualities and usage.

Lists are created using square brackets:

Example

Create a List:

thislist = ["apple""banana""cherry"]
print(thislist)

Try it Yourself »


List Items

List items are ordered, changeable, and allow duplicate values.

List items are indexed, the first item has index [0], the second item has index [1] etc.


Ordered

When we say that lists are ordered, it means that the items have a defined order, and that order will not change.

If you add new items to a list, the new items will be placed at the end of the list.

Note: There are some list methods that will change the order, but in general: the order of the items will not change.


Changeable

The list is changeable, meaning that we can change, add, and remove items in a list after it has been created.


Allow Duplicates

Since lists are indexed, lists can have items with the same value:

Example

Lists allow duplicate values:

thislist = ["apple""banana""cherry""apple""cherry"]
print(thislist)

Try it Yourself »


 

List Length

To determine how many items a list has, use the len() function:

Example

Print the number of items in the list:

thislist = ["apple""banana""cherry"]
print(len(thislist))

Try it Yourself »


List Items – Data Types

List items can be of any data type:

Example

String, int and boolean data types:

list1 = ["apple", "banana""cherry"]
list2 = [15793]
list3 = [TrueFalseFalse]

Try it Yourself »

A list can contain different data types:

Example

A list with strings, integers and boolean values:

list1 = ["abc"34True40"male"]

Try it Yourself »


type()

From Python’s perspective, lists are defined as objects with the data type ‘list’:

'list'>

Example

What is the data type of a list?

mylist = ["apple""banana""cherry"]
print(type(mylist))

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The list() Constructor

It is also possible to use the list() constructor when creating a new list.

Example

Using the list() constructor to make a List:

thislist = list(("apple""banana""cherry")) # note the double round-brackets
print(thislist)

Try it Yourself »


Python Collections (Arrays)

There are four collection data types in the Python programming language:

  • List is a collection which is ordered and changeable. Allows duplicate members.
  • Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
  • Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
  • Dictionary is a collection which is ordered** and changeable. No duplicate members.

*Set items are unchangeable, but you can remove and/or add items whenever you like.

**As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.

Python – Access List Items

Access Items

List items are indexed and you can access them by referring to the index number:

Example

Print the second item of the list:

thislist = ["apple""banana", "cherry"]
print(thislist[1])

Try it Yourself »

Note: The first item has index 0.

Negative Indexing

Negative indexing means start from the end

-1 refers to the last item, -2 refers to the second last item etc.

Example

Print the last item of the list:

thislist = ["apple""banana""cherry"]
print(thislist[-1])

Try it Yourself »

Range of Indexes

You can specify a range of indexes by specifying where to start and where to end the range.

When specifying a range, the return value will be a new list with the specified items.

Example

Return the third, fourth, and fifth item:

thislist = ["apple""banana""cherry""orange""kiwi", "melon""mango"]
print(thislist[2:5])

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Note: The search will start at index 2 (included) and end at index 5 (not included).

Remember that the first item has index 0.

By leaving out the start value, the range will start at the first item:

Example

This example returns the items from the beginning to, but NOT including, “kiwi”:

thislist = ["apple""banana""cherry""orange""kiwi""melon""mango"]
print(thislist[:4])

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By leaving out the end value, the range will go on to the end of the list:

Example

This example returns the items from “cherry” to the end:

thislist = ["apple""banana", "cherry""orange""kiwi""melon""mango"]
print(thislist[2:])

Try it Yourself »

 

Python – Change List Items

Change Item Value

To change the value of a specific item, refer to the index number:

Example

Change the second item:

thislist = ["apple""banana""cherry"]
thislist[1] = "blackcurrant"
print(thislist)

Try it Yourself »


Change a Range of Item Values

To change the value of items within a specific range, define a list with the new values, and refer to the range of index numbers where you want to insert the new values:

Example

Change the values “banana” and “cherry” with the values “blackcurrant” and “watermelon”:

thislist = ["apple""banana""cherry""orange""kiwi""mango"]
thislist[1:3] = ["blackcurrant""watermelon"]
print(thislist)

Try it Yourself »

If you insert more items than you replace, the new items will be inserted where you specified, and the remaining items will move accordingly:

Example

Change the second value by replacing it with two new values:

thislist = ["apple""banana""cherry"]
thislist[1:2] = ["blackcurrant""watermelon"]
print(thislist)

Try it Yourself »

Note: The length of the list will change when the number of items inserted does not match the number of items replaced.

If you insert less items than you replace, the new items will be inserted where you specified, and the remaining items will move accordingly:

Example

Change the second and third value by replacing it with one value:

thislist = ["apple", "banana""cherry"]
thislist[1:3] = ["watermelon"]
print(thislist)

Try it Yourself »


Insert Items

To insert a new list item, without replacing any of the existing values, we can use the insert() method.

The insert() method inserts an item at the specified index:

Example

Insert “watermelon” as the third item:

thislist = ["apple""banana""cherry"]
thislist.insert(2"watermelon")
print(thislist)

Try it Yourself »

 

Python – Add List Items

Append Items

To add an item to the end of the list, use the append() method:

Example

Using the append() method to append an item:

thislist = ["apple""banana""cherry"]
thislist.append("orange")
print(thislist)

Try it Yourself »


Insert Items

To insert a list item at a specified index, use the insert() method.

The insert() method inserts an item at the specified index:

Example

Insert an item as the second position:

thislist = ["apple""banana""cherry"]
thislist.insert(1"orange")
print(thislist)

Try it Yourself »

Note: As a result of the examples above, the lists will now contain 4 items.


Extend List

To append elements from another list to the current list, use the extend() method.

Example

Add the elements of tropical to thislist:

thislist = ["apple""banana""cherry"]
tropical = ["mango""pineapple""papaya"]
thislist.extend(tropical)
print(thislist)

Try it Yourself »

The elements will be added to the end of the list.


Add Any Iterable

The extend() method does not have to append lists, you can add any iterable object (tuples, sets, dictionaries etc.).

Example

Add elements of a tuple to a list:

thislist = ["apple""banana""cherry"]
thistuple = ("kiwi""orange")
thislist.extend(thistuple)
print(thislist)

Try it Yourself »

Python – Remove List Items

Remove Specified Item

The remove() method removes the specified item.

Example

Remove “banana”:

thislist = ["apple""banana""cherry"]
thislist.remove("banana")
print(thislist)

Try it Yourself »


Remove Specified Index

The pop() method removes the specified index.

Example

Remove the second item:

thislist = ["apple""banana""cherry"]
thislist.pop(1)
print(thislist)

Try it Yourself »

If you do not specify the index, the pop() method removes the last item.

Example

Remove the last item:

thislist = ["apple""banana""cherry"]
thislist.pop()
print(thislist)

Try it Yourself »

The del keyword also removes the specified index:

Example

Remove the first item:

thislist = ["apple""banana""cherry"]
del thislist[0]
print(thislist)

Try it Yourself »

The del keyword can also delete the list completely.

Example

Delete the entire list:

thislist = ["apple""banana""cherry"]
del thislist

Try it Yourself »


Clear the List

The clear() method empties the list.

The list still remains, but it has no content.

Example

Clear the list content:

thislist = ["apple""banana""cherry"]
thislist.clear()
print(thislist)

Python – Loop Lists

Loop Through a List

You can loop through the list items by using a for loop:

Example

Print all items in the list, one by one:

thislist = ["apple""banana""cherry"]
for x in thislist:
  print(x)

Try it Yourself »

Learn more about for loops in our Python For Loops Chapter.


Loop Through the Index Numbers

You can also loop through the list items by referring to their index number.

Use the range() and len() functions to create a suitable iterable.

Example

Print all items by referring to their index number:

thislist = ["apple""banana""cherry"]
for i in range(len(thislist)):
print(thislist[i])

Try it Yourself »

The iterable created in the example above is [0, 1, 2].


 

Using a While Loop

You can loop through the list items by using a while loop.

Use the len() function to determine the length of the list, then start at 0 and loop your way through the list items by refering to their indexes.

Remember to increase the index by 1 after each iteration.

Example

Print all items, using a while loop to go through all the index numbers

thislist = ["apple""banana""cherry"]
i = 0
while i < len(thislist):
print(thislist[i])
  i = i + 1

Try it Yourself »

Learn more about while loops in our Python While Loops Chapter.


Looping Using List Comprehension

List Comprehension offers the shortest syntax for looping through lists:

Example

A short hand for loop that will print all items in a list:

thislist = ["apple""banana""cherry"]
[print(x) for x in thislist]

Try it Yourself »

Learn more about list comprehension in the next chapter: List Comprehension.

Python – List Comprehension

List Comprehension

List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.

Example:

Based on a list of fruits, you want a new list, containing only the fruits with the letter “a” in the name.

Without list comprehension you will have to write a for statement with a conditional test inside:

Example

fruits = ["apple""banana""cherry""kiwi""mango"]
newlist = []


for x in fruits:
  if "a" in x:
    newlist.append(x)

print(newlist)

Try it Yourself »

With list comprehension you can do all that with only one line of code:

Example

fruits = ["apple""banana""cherry""kiwi""mango"]

newlist = [x for x in fruits if "a" in x]

print(newlist)

Try it Yourself »


The Syntax

newlist = [expression for item in iterable if condition == True]

The return value is a new list, leaving the old list unchanged.


Condition

The condition is like a filter that only accepts the items that valuate to True.

Example

Only accept items that are not “apple”:

newlist = [x for x in fruits if x != "apple"]

Try it Yourself »

The condition if x != “apple”  will return True for all elements other than “apple”, making the new list contain all fruits except “apple”.

The condition is optional and can be omitted:

Example

With no if statement:

newlist = [x for x in fruits]

Try it Yourself »


Iterable

The iterable can be any iterable object, like a list, tuple, set etc.

Example

You can use the range() function to create an iterable:

newlist = [x for x in range(10)]

Try it Yourself »

Same example, but with a condition:

Example

Accept only numbers lower than 5:

newlist = [x for x in range(10if x < 5]

Try it Yourself »


Expression

The expression is the current item in the iteration, but it is also the outcome, which you can manipulate before it ends up like a list item in the new list:

Example

Set the values in the new list to upper case:

newlist = [x.upper() for x in fruits]

Try it Yourself »

You can set the outcome to whatever you like:

Example

Set all values in the new list to ‘hello’:

newlist = ['hello' for x in fruits]

Try it Yourself »

The expression can also contain conditions, not like a filter, but as a way to manipulate the outcome:

Example

Return “orange” instead of “banana”:

newlist = [x if x != "banana" else "orange" for x in fruits]

Try it Yourself »

The expression in the example above says:

“Return the item if it is not banana, if it is banana return orange”

Python – Sort Lists

Sort List Alphanumerically

List objects have a sort() method that will sort the list alphanumerically, ascending, by default:

Example

Sort the list alphabetically:

thislist = ["orange""mango""Kiwi""pineapple", "banana"]
thislist.sort()
print(thislist)

Try it Yourself »

Example

Sort the list numerically:

thislist = [10050658223]
thislist.sort()
print(thislist)

Try it Yourself »


Sort Descending

To sort descending, use the keyword argument reverse = True:

Example

Sort the list descending:

thislist = ["banana""Orange""Kiwi""cherry"]
thislist.sort(reverse = True)
print(thislist)

Try it Yourself »

Example

Sort the list descending:

thislist = [10050658223]
thislist.sort(reverse = True)
print(thislist)

Try it Yourself »


Customize Sort Function

You can also customize your own function by using the keyword argument .key = function

The function will return a number that will be used to sort the list (the lowest number first):

Example

Sort the list based on how close the number is to 50:

def myfunc(n):
  return abs(n - 50)


thislist = [10050658223]
thislist.sort(key = myfunc)
print(thislist)

Try it Yourself »


Case Insensitive Sort

By default the sort() method is case sensitive, resulting in all capital letters being sorted before lower case letters:

Example

Case sensitive sorting can give an unexpected result:

thislist = ["banana""Orange""Kiwi""cherry"]
thislist.sort()
print(thislist)

Try it Yourself »

Luckily we can use built-in functions as key functions when sorting a list.

So if you want a case-insensitive sort function, use str.lower as a key function:

Example

Perform a case-insensitive sort of the list:

thislist = ["banana""Orange""Kiwi""cherry"]
thislist.sort(key = str.lower)
print(thislist)

Try it Yourself »


Reverse Order

What if you want to reverse the order of a list, regardless of the alphabet?

The reverse() method reverses the current sorting order of the elements.

Example

Reverse the order of the list items:

thislist = ["banana""Orange""Kiwi""cherry"]
thislist.reverse()
print(thislist)

Try it Yourself »

Python – Copy Lists

Copy a List

You cannot copy a list simply by typing list2 = list1, because: list2 will only be a reference to list1, and changes made in list1 will automatically also be made in list2.

There are ways to make a copy, one way is to use the built-in List method copy().

Example

Make a copy of a list with the copy() method:

thislist = ["apple""banana""cherry"]
mylist = thislist.copy()
print(mylist)

Try it Yourself »

Another way to make a copy is to use the built-in method list().

Example

Make a copy of a list with the list() method:

thislist = ["apple""banana""cherry"]
mylist = list(thislist)
print(mylist)

Try it Yourself »

Python – Join Lists

Join Two Lists

There are several ways to join, or concatenate, two or more lists in Python.

One of the easiest ways are by using the + operator.

Example

Join two list:

list1 = ["a""b", "c"]
list2 = [123]


list3 = list1 + list2
print(list3)

Try it Yourself »

Another way to join two lists is by appending all the items from list2 into list1, one by one:

Example

Append list2 into list1:

list1 = ["a""b", "c"]
list2 = [123]


for x in list2:
  list1.append(x)

print(list1)

Try it Yourself »

Or you can use the extend() method, which purpose is to add elements from one list to another list:

Example

Use the extend() method to add list2 at the end of list1:

list1 = ["a""b" , "c"]
list2 = [123]


list1.extend(list2)
print(list1)

Try it Yourself »

Python – List Methods

List Methods

Python has a set of built-in methods that you can use on lists.

MethodDescription
append()Adds an element at the end of the list
clear()Removes all the elements from the list
copy()Returns a copy of the list
count()Returns the number of elements with the specified value
extend()Add the elements of a list (or any iterable), to the end of the current list
index()Returns the index of the first element with the specified value
insert()Adds an element at the specified position
pop()Removes the element at the specified position
remove()Removes the item with the specified value
reverse()Reverses the order of the list
sort()Sorts the list
 
 

Python List Exercises

Test Yourself With Exercises

Now you have learned a lot about lists, and how to use them in Python.

Are you ready for a test?

Try to insert the missing part to make the code work as expected:

Exercise:

Print the second item in the fruits list.

fruits = ["apple", "banana", "cherry"]
print()

Go to the Exercise section and test all of our Python List Exercises:

Python List Exercises

Python Tuples

Python Tuples

mytuple = ("apple""banana""cherry")

Tuple

Tuples are used to store multiple items in a single variable.

Tuple is one of 4 built-in data types in Python used to store collections of data, the other 3 are ListSet, and Dictionary, all with different qualities and usage.

A tuple is a collection which is ordered and unchangeable.

Tuples are written with round brackets.

Example

Create a Tuple:

thistuple = ("apple""banana""cherry")
print(thistuple)

Try it Yourself »


Tuple Items

Tuple items are ordered, unchangeable, and allow duplicate values.

Tuple items are indexed, the first item has index [0], the second item has index [1] etc.


Ordered

When we say that tuples are ordered, it means that the items have a defined order, and that order will not change.


Unchangeable

Tuples are unchangeable, meaning that we cannot change, add or remove items after the tuple has been created.


Allow Duplicates

Since tuples are indexed, they can have items with the same value:

Example

Tuples allow duplicate values:

thistuple = ("apple""banana""cherry", "apple", "cherry")
print(thistuple)

Try it Yourself »


Tuple Length

To determine how many items a tuple has, use the len() function:

Example

Print the number of items in the tuple:

thistuple = ("apple""banana""cherry")
print(len(thistuple))

Try it Yourself »


Create Tuple With One Item

To create a tuple with only one item, you have to add a comma after the item, otherwise Python will not recognize it as a tuple.

Example

One item tuple, remember the comma:

thistuple = ("apple",)
print(type(thistuple))


#NOT a tuple
thistuple = ("apple")
print(type(thistuple))

Try it Yourself »


Tuple Items – Data Types

Tuple items can be of any data type:

Example

String, int and boolean data types:

tuple1 = ("apple""banana""cherry")
tuple2 = (15793)
tuple3 = (TrueFalseFalse)

Try it Yourself »

A tuple can contain different data types:

Example

A tuple with strings, integers and boolean values:

tuple1 = ("abc"34True40"male")

Try it Yourself »


type()

From Python’s perspective, tuples are defined as objects with the data type ‘tuple’:

<class ‘tuple’>

Example

What is the data type of a tuple?

mytuple = ("apple""banana""cherry")
print(type(mytuple))

Try it Yourself »


The tuple() Constructor

It is also possible to use the tuple() constructor to make a tuple.

Example

Using the tuple() method to make a tuple:

thistuple = tuple(("apple""banana""cherry")) # note the double round-brackets
print(thistuple)

Try it Yourself »


Python Collections (Arrays)

There are four collection data types in the Python programming language:

  • List is a collection which is ordered and changeable. Allows duplicate members.
  • Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
  • Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
  • Dictionary is a collection which is ordered** and changeable. No duplicate members.

*Set items are unchangeable, but you can remove and/or add items whenever you like.

**As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.

Python – Access Tuple Items

Access Tuple Items

You can access tuple items by referring to the index number, inside square brackets:

Example

Print the second item in the tuple:

thistuple = ("apple""banana""cherry")

print(thistuple[1])

Try it Yourself »

Note: The first item has index 0.


Negative Indexing

Negative indexing means start from the end.

-1 refers to the last item, -2 refers to the second last item etc.

Example

Print the last item of the tuple:

thistuple = ("apple""banana""cherry")
print(thistuple[-1])

Try it Yourself »


Range of Indexes

You can specify a range of indexes by specifying where to start and where to end the range.

When specifying a range, the return value will be a new tuple with the specified items.

Example

Return the third, fourth, and fifth item:

thistuple = ("apple""banana""cherry""orange""kiwi""melon""mango")
print(thistuple[2:5])

Try it Yourself »

Note: The search will start at index 2 (included) and end at index 5 (not included).

Remember that the first item has index 0.

By leaving out the start value, the range will start at the first item:

Example

This example returns the items from the beginning to, but NOT included, “kiwi”:

thistuple = ("apple""banana""cherry""orange""kiwi""melon""mango")
print(thistuple[:4])

Try it Yourself »

By leaving out the end value, the range will go on to the end of the list:

Example

This example returns the items from “cherry” and to the end:

thistuple = (“apple”“banana”“cherry”“orange”“kiwi”“melon”“mango”)
print(thistuple[2:])

Try it Yourself »


Range of Negative Indexes

Specify negative indexes if you want to start the search from the end of the tuple:

Example

This example returns the items from index -4 (included) to index -1 (excluded)

thistuple = ("apple""banana""cherry""orange""kiwi""melon""mango")
print(thistuple[-4:-1])

Try it Yourself »


Check if Item Exists

To determine if a specified item is present in a tuple use the in keyword:

Example

Check if “apple” is present in the tuple:

thistuple = ("apple""banana""cherry"
if "apple" in thistuple:
  print("Yes, 'apple' is in the fruits tuple")

Try it Yourself »

 

Python – Update Tuples

Tuples are unchangeable, meaning that you cannot change, add, or remove items once the tuple is created.

But there are some workarounds.


Change Tuple Values

Once a tuple is created, you cannot change its values. Tuples are unchangeable, or immutable as it also is called.

But there is a workaround. You can convert the tuple into a list, change the list, and convert the list back into a tuple.

Example

Convert the tuple into a list to be able to change it:

x = ("apple""banana""cherry")
y = list(x)
y[1] = "kiwi"
x = tuple(y)


print(x)

Try it Yourself »


Add Items

Since tuples are immutable, they do not have a build-in append() method, but there are other ways to add items to a tuple.

1. Convert into a list: Just like the workaround for changing a tuple, you can convert it into a list, add your item(s), and convert it back into a tuple.

Example

Convert the tuple into a list, add “orange”, and convert it back into a tuple:

thistuple = ("apple""banana""cherry")
y = list(thistuple)
y.append("orange")
thistuple = tuple(y)

Try it Yourself »

2. Add tuple to a tuple. You are allowed to add tuples to tuples, so if you want to add one item, (or many), create a new tuple with the item(s), and add it to the existing tuple:

Example

Create a new tuple with the value “orange”, and add that tuple:

thistuple = ("apple""banana""cherry")
y = ("orange",)
thistuple += y


print(thistuple)

Try it Yourself »

Note: When creating a tuple with only one item, remember to include a comma after the item, otherwise it will not be identified as a tuple.


Remove Items

Note: You cannot remove items in a tuple.

Tuples are unchangeable, so you cannot remove items from it, but you can use the same workaround as we used for changing and adding tuple items:

Example

Convert the tuple into a list, remove “apple”, and convert it back into a tuple:

thistuple = ("apple""banana""cherry")
y = list(thistuple)
y.remove("apple")
thistuple = tuple(y)

Try it Yourself »

Or you can delete the tuple completely:

Example

The del keyword can delete the tuple completely:

thistuple = ("apple""banana""cherry")
del thistuple
print(thistuple) #this will raise an error because the tuple no longer exists

Try it Yourself »

Python – Unpack Tuples

Unpacking a Tuple

When we create a tuple, we normally assign values to it. This is called “packing” a tuple:

Example

Packing a tuple:

fruits = ("apple""banana""cherry")

Try it Yourself »

But, in Python, we are also allowed to extract the values back into variables. This is called “unpacking”:

Example

Unpacking a tuple:

fruits = ("apple""banana""cherry")

(green, yellow, red) = fruits

print(green)
print(yellow)
print(red)

Try it Yourself »

Note: The number of variables must match the number of values in the tuple, if not, you must use an asterisk to collect the remaining values as a list.


 

Using Asterisk*

If the number of variables is less than the number of values, you can add an * to the variable name and the values will be assigned to the variable as a list:

Example

Assign the rest of the values as a list called “red”:

fruits = ("apple""banana""cherry""strawberry""raspberry")

(green, yellow, *red) = fruits

print(green)
print(yellow)
print(red)

Try it Yourself »

If the asterisk is added to another variable name than the last, Python will assign values to the variable until the number of values left matches the number of variables left.

Example

Add a list of values the “tropic” variable:

fruits = ("apple""mango""papaya""pineapple""cherry")

(green, *tropic, red) = fruits

print(green)
print(tropic)
print(red)

Try it Yourself »

Python – Loop Tuples

Loop Through a Tuple

You can loop through the tuple items by using a for loop.

Example

Iterate through the items and print the values:

thistuple = ("apple""banana""cherry")
for in thistuple:
print(x)

Try it Yourself »

Learn more about for loops in our Python For Loops Chapter.


Loop Through the Index Numbers

You can also loop through the tuple items by referring to their index number.

Use the range() and len() functions to create a suitable iterable.

Example

Print all items by referring to their index number:

thistuple = ("apple""banana""cherry")
for in range(len(thistuple)):
print(thistuple[i])

Try it Yourself »


 

Using a While Loop

You can loop through the list items by using a while loop.

Use the len() function to determine the length of the tuple, then start at 0 and loop your way through the tuple items by refering to their indexes.

Remember to increase the index by 1 after each iteration.

Example

Print all items, using a while loop to go through all the index numbers:

thistuple = ("apple""banana""cherry")
i = 0
while i < len(thistuple):
print(thistuple[i])
  i = i + 1

Try it Yourself »

Python – Join Tuples

Join Two Tuples

To join two or more tuples you can use the + operator:

Example

Join two tuples:

tuple1 = ("a""b" , "c")
tuple2 = (123)


tuple3 = tuple1 + tuple2
print(tuple3)

Try it Yourself »


Multiply Tuples

If you want to multiply the content of a tuple a given number of times, you can use the * operator:

Example

Multiply the fruits tuple by 2:

fruits = ("apple""banana""cherry")
mytuple = fruits * 2


print(mytuple)

Try it Yourself »

Python – Tuple Methods

Tuple Methods

Python has two built-in methods that you can use on tuples.

MethodDescription
count()Returns the number of times a specified value occurs in a tuple
index()Searches the tuple for a specified value and returns the position of where it was found

Python – Tuple Exercises

Test Yourself With Exercises

Now you have learned a lot about tuples, and how to use them in Python.

Are you ready for a test?

Try to insert the missing part to make the code work as expected:

Exercise:

Print the first item in the fruits tuple.

fruits = "apple"
print()

Go to the Exercise section and test all of our Python Tuple Exercises:

Python Tuple Exercises

Python Sets

Python Sets

myset = {"apple""banana""cherry"}

Set

Sets are used to store multiple items in a single variable.

Set is one of 4 built-in data types in Python used to store collections of data, the other 3 are ListTuple, and Dictionary, all with different qualities and usage.

A set is a collection which is unorderedunchangeable*, and unindexed.

* Note: Set items are unchangeable, but you can remove items and add new items.

Sets are written with curly brackets.

Example

Create a Set:

thisset = {"apple""banana""cherry"}
print(thisset)

Try it Yourself »

Note: Sets are unordered, so you cannot be sure in which order the items will appear.


Set Items

Set items are unordered, unchangeable, and do not allow duplicate values.


Unordered

Unordered means that the items in a set do not have a defined order.

Set items can appear in a different order every time you use them, and cannot be referred to by index or key.


Unchangeable

Set items are unchangeable, meaning that we cannot change the items after the set has been created.

Once a set is created, you cannot change its items, but you can remove items and add new items.


Duplicates Not Allowed

Sets cannot have two items with the same value.

Example

Duplicate values will be ignored:

thisset = {"apple""banana""cherry""apple"}

print(thisset)

Try it Yourself »


 

Get the Length of a Set

To determine how many items a set has, use the len() function.

Example

Get the number of items in a set:

thisset = {"apple""banana""cherry"}

print(len(thisset))

Try it Yourself »


Set Items – Data Types

Set items can be of any data type:

Example

String, int and boolean data types:

set1 = {"apple""banana""cherry"}
set2 = {15793}
set3 = {TrueFalseFalse}

Try it Yourself »

A set can contain different data types:

Example

A set with strings, integers and boolean values:

set1 = {"abc"34True40"male"}

Try it Yourself »


type()

From Python’s perspective, sets are defined as objects with the data type ‘set’:

<class ‘set’>

Example

What is the data type of a set?

myset = {"apple""banana""cherry"}
print(type(myset))

Try it Yourself »


The set() Constructor

It is also possible to use the set() constructor to make a set.

Example

Using the set() constructor to make a set:

thisset = set(("apple""banana""cherry")) # note the double round-brackets
print(thisset)

Try it Yourself »


Python Collections (Arrays)

There are four collection data types in the Python programming language:

  • List is a collection which is ordered and changeable. Allows duplicate members.
  • Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
  • Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
  • Dictionary is a collection which is ordered** and changeable. No duplicate members.

*Set items are unchangeable, but you can remove items and add new items.

**As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.

Python – Access Set Items

Access Items

You cannot access items in a set by referring to an index or a key.

But you can loop through the set items using a for loop, or ask if a specified value is present in a set, by using the in keyword.

Example

Loop through the set, and print the values:

thisset = {"apple""banana""cherry"}

for in thisset:
  print(x)

Try it Yourself »

Example

Check if “banana” is present in the set:

thisset = {"apple""banana""cherry"}

print("banana" in thisset)

Try it Yourself »


Change Items

Once a set is created, you cannot change its items, but you can add new items.

Python – Add Set Items

Add Items

Once a set is created, you cannot change its items, but you can add new items.

To add one item to a set use the add() method.

Example

Add an item to a set, using the add() method:

thisset = {"apple""banana""cherry"}

thisset.add("orange")

print(thisset)

Try it Yourself »


Add Sets

To add items from another set into the current set, use the update() method.

Example

Add elements from tropical into thisset:

thisset = {"apple""banana""cherry"}
tropical = {"pineapple""mango""papaya"}


thisset.update(tropical)

print(thisset)

Try it Yourself »


Add Any Iterable

The object in the update() method does not have to be a set, it can be any iterable object (tuples, lists, dictionaries etc.).

Example

Add elements of a list to at set:

thisset = {"apple""banana""cherry"}
mylist = ["kiwi", "orange"]


thisset.update(mylist)

print(thisset)

Try it Yourself »

Python – Remove Set Items

Remove Item

To remove an item in a set, use the remove(), or the discard() method.

Example

Remove “banana” by using the remove() method:

thisset = {"apple""banana""cherry"}

thisset.remove("banana")

print(thisset)

Try it Yourself »

Note: If the item to remove does not exist, remove() will raise an error.

Example

Remove “banana” by using the discard() method:

thisset = {"apple""banana""cherry"}

thisset.discard("banana")

print(thisset)

Try it Yourself »

Note: If the item to remove does not exist, discard() will NOT raise an error.

You can also use the pop() method to remove an item, but this method will remove the last item. Remember that sets are unordered, so you will not know what item that gets removed.

The return value of the pop() method is the removed item.

Example

Remove the last item by using the pop() method:

thisset = {"apple""banana""cherry"}

x = thisset.pop()

print(x)

print(thisset)

Try it Yourself »

Note: Sets are unordered, so when using the pop() method, you do not know which item that gets removed.

Example

The clear() method empties the set:

thisset = {"apple""banana""cherry"}

thisset.clear()

print(thisset)

Try it Yourself »

Example

The del keyword will delete the set completely:

thisset = {"apple""banana""cherry"}

del thisset

print(thisset)

Try it Yourself »

Python – Loop Sets

Loop Items

You can loop through the set items by using a for loop:

Example

Loop through the set, and print the values:

thisset = {"apple""banana""cherry"}

for in thisset:
print(x)

Try it Yourself »

Python – Join Sets

Join Two Sets

There are several ways to join two or more sets in Python.

You can use the union() method that returns a new set containing all items from both sets, or the update() method that inserts all the items from one set into another:

Example

The union() method returns a new set with all items from both sets:

set1 = {"a""b" , "c"}
set2 = {123}


set3 = set1.union(set2)
print(set3)

Try it Yourself »

Example

The update() method inserts the items in set2 into set1:

set1 = {"a""b" , "c"}
set2 = {123}


set1.update(set2)
print(set1)

Try it Yourself »

Note: Both union() and update() will exclude any duplicate items.


Keep ONLY the Duplicates

The intersection_update() method will keep only the items that are present in both sets.

Example

Keep the items that exist in both set x, and set y:

x = {"apple""banana""cherry"}
y = {"google""microsoft""apple"}


x.intersection_update(y)

print(x)

Try it Yourself »

The intersection() method will return a new set, that only contains the items that are present in both sets.

Example

Return a set that contains the items that exist in both set x, and set y:

x = {"apple""banana""cherry"}
y = {"google""microsoft""apple"}


z = x.intersection(y)

print(z)

Try it Yourself »


Keep All, But NOT the Duplicates

The symmetric_difference_update() method will keep only the elements that are NOT present in both sets.

Example

Keep the items that are not present in both sets:

x = {"apple""banana""cherry"}
y = {"google""microsoft""apple"}


x.symmetric_difference_update(y)

print(x)

Try it Yourself »

The symmetric_difference() method will return a new set, that contains only the elements that are NOT present in both sets.

Example

Return a set that contains all items from both sets, except items that are present in both:

x = {"apple""banana""cherry"}
y = {"google""microsoft""apple"}


z = x.symmetric_difference(y)

print(z)

Try it Yourself »

Python – Set Methods

Set Methods

Python has a set of built-in methods that you can use on sets.

MethodDescription
add()Adds an element to the set
clear()Removes all the elements from the set
copy()Returns a copy of the set
difference()Returns a set containing the difference between two or more sets
difference_update()Removes the items in this set that are also included in another, specified set
discard()Remove the specified item
intersection()Returns a set, that is the intersection of two other sets
intersection_update()Removes the items in this set that are not present in other, specified set(s)
isdisjoint()Returns whether two sets have a intersection or not
issubset()Returns whether another set contains this set or not
issuperset()Returns whether this set contains another set or not
pop()Removes an element from the set
remove()Removes the specified element
symmetric_difference()Returns a set with the symmetric differences of two sets
symmetric_difference_update()inserts the symmetric differences from this set and another
union()Return a set containing the union of sets
update()Update the set with the union of this set and others
 
 

Python – Set Exercises

Test Yourself With Exercises

Now you have learned a lot about sets, and how to use them in Python.

Are you ready for a test?

Try to insert the missing part to make the code work as expected:


Exercise:

Check if “apple” is present in the fruits set.

fruits = {"apple", "banana", "cherry"}
if "apple"  fruits:
  print("Yes, apple is a fruit!")

Go to the Exercise section and test all of our Python Set Exercises:

Python Set Exercises

Python Dictionaries

Python Dictionaries

thisdict = {
  "brand""Ford",
  "model""Mustang",
  "year": 1964
}

Dictionary

Dictionaries are used to store data values in key:value pairs.

A dictionary is a collection which is ordered*, changeable and do not allow duplicates.

As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

Dictionaries are written with curly brackets, and have keys and values:

Example

Create and print a dictionary:

thisdict = {
  "brand""Ford",
  "model""Mustang",
  "year"1964
}
print(thisdict)

Try it Yourself »


Dictionary Items

Dictionary items are ordered, changeable, and does not allow duplicates.

Dictionary items are presented in key:value pairs, and can be referred to by using the key name.

Example

Print the “brand” value of the dictionary:

thisdict = {
  "brand""Ford",
  "model""Mustang",
  "year"1964
}
print(thisdict["brand"])

Try it Yourself »


Ordered or Unordered?

As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

When we say that dictionaries are ordered, it means that the items have a defined order, and that order will not change.

Unordered means that the items does not have a defined order, you cannot refer to an item by using an index.


Changeable

Dictionaries are changeable, meaning that we can change, add or remove items after the dictionary has been created.


Duplicates Not Allowed

Dictionaries cannot have two items with the same key:

Example

Duplicate values will overwrite existing values:

thisdict = {
  "brand""Ford",
  "model""Mustang",
  "year"1964,
  "year"2020
}
print(thisdict)

Try it Yourself »


Dictionary Length

To determine how many items a dictionary has, use the len() function:

Example

Print the number of items in the dictionary:

print(len(thisdict))

Try it Yourself »


Dictionary Items – Data Types

The values in dictionary items can be of any data type:

Example

String, int, boolean, and list data types:

thisdict = {
  "brand""Ford",
  "electric": False,
  "year"1964,
  "colors": ["red""white""blue"]
}

Try it Yourself »


type()

From Python’s perspective, dictionaries are defined as objects with the data type ‘dict’:

<class ‘dict’>

Example

Print the data type of a dictionary:

thisdict = {
  "brand""Ford",
  "model""Mustang",
  "year"1964
}
print(type(thisdict))

Try it Yourself »


Python Collections (Arrays)

There are four collection data types in the Python programming language:

  • List is a collection which is ordered and changeable. Allows duplicate members.
  • Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
  • Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
  • Dictionary is a collection which is ordered** and changeable. No duplicate members.

*Set items are unchangeable, but you can remove and/or add items whenever you like.

**As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.

Python – Access Dictionary Items

Accessing Items

You can access the items of a dictionary by referring to its key name, inside square brackets:

Example

Get the value of the “model” key:

thisdict = {
  "brand""Ford",
  "model""Mustang",
  "year"1964
}
x = thisdict["model"]

Try it Yourself »

There is also a method called get() that will give you the same result:

Example

Get the value of the “model” key:

x = thisdict.get("model")

Try it Yourself »


Get Keys

The keys() method will return a list of all the keys in the dictionary.

Example

Get a list of the keys:

x = thisdict.keys()

Try it Yourself »

The list of the keys is a view of the dictionary, meaning that any changes done to the dictionary will be reflected in the keys list.

Example

Add a new item to the original dictionary, and see that the keys list gets updated as well:

car = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}


x = car.keys()

print(x) #before the change

car["color"] = "white"

print(x) #after the change

Try it Yourself »

Get Values

The values() method will return a list of all the values in the dictionary.

Example

Get a list of the values:

x = thisdict.values()
Try it Yourself »

The list of the values is a view of the dictionary, meaning that any changes done to the dictionary will be reflected in the values list.

Example

Make a change in the original dictionary, and see that the values list gets updated as well:

car = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}

x = car.values()

print(x) #before the change

car["year"] = 2020

print(x) #after the change
Try it Yourself »

Example

Add a new item to the original dictionary, and see that the values list gets updated as well:

car = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}

x = car.values()

print(x) #before the change

car["color"] = "red"

print(x) #after the change
Try it Yourself »

Get Items

The items() method will return each item in a dictionary, as tuples in a list.

Example

Get a list of the key:value pairs

x = thisdict.items()
Try it Yourself »

The returned list is a view of the items of the dictionary, meaning that any changes done to the dictionary will be reflected in the items list.

Example

Make a change in the original dictionary, and see that the items list gets updated as well:

car = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}

x = car.items()

print(x) #before the change

car["year"] = 2020

print(x) #after the change
Try it Yourself »

Example

Add a new item to the original dictionary, and see that the items list gets updated as well:

car = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}

x = car.items()

print(x) #before the change

car["color"] = "red"

print(x) #after the change
Try it Yourself »

Check if Key Exists

To determine if a specified key is present in a dictionary use the in keyword:

Example

Check if “model” is present in the dictionary:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
if "model" in thisdict:
  print("Yes, 'model' is one of the keys in the thisdict dictionary")

Python – Change Dictionary Items

Change Values

You can change the value of a specific item by referring to its key name:

Example

Change the “year” to 2018:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
thisdict["year"] = 2018

Try it Yourself »


Update Dictionary

The update() method will update the dictionary with the items from the given argument.

The argument must be a dictionary, or an iterable object with key:value pairs.

Example

Update the “year” of the car by using the update() method:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
thisdict.update({"year"2020})

Try it Yourself »

Python – Add Dictionary Items

Adding Items

Adding an item to the dictionary is done by using a new index key and assigning a value to it:

Example

thisdict = {
“brand”“Ford”,
  “model”“Mustang”,
  “year”1964
}
thisdict[“color”] = “red”
print(thisdict)

Try it Yourself »


Update Dictionary

The update() method will update the dictionary with the items from a given argument. If the item does not exist, the item will be added.

The argument must be a dictionary, or an iterable object with key:value pairs.

Example

Add a color item to the dictionary by using the update() method:

thisdict = {
“brand”“Ford”,
  “model”“Mustang”,
  “year”1964
}
thisdict.update({“color”“red”})

Try it Yourself »

Python – Remove Dictionary Items

Loop Through a Dictionary

You can loop through a dictionary by using a for loop.

When looping through a dictionary, the return value are the keys of the dictionary, but there are methods to return the values as well.

Example

Print all key names in the dictionary, one by one:

for in thisdict:
  print(x)

Try it Yourself »

Example

Print all values in the dictionary, one by one:

for in thisdict:
  print(thisdict[x])

Try it Yourself »

Example

You can also use the values() method to return values of a dictionary:

for in thisdict.values():
  print(x)

Try it Yourself »

Example

You can use the keys() method to return the keys of a dictionary:

for in thisdict.keys():
  print(x)

Try it Yourself »

Example

Loop through both keys and values, by using the items() method:

for x, y in thisdict.items():
  print(x, y)

Try it Yourself »

Removing Items

There are several methods to remove items from a dictionary:

Example

The pop() method removes the item with the specified key name:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
thisdict.pop("model")
print(thisdict)

Try it Yourself »

Example

The popitem() method removes the last inserted item (in versions before 3.7, a random item is removed instead):

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
thisdict.popitem()
print(thisdict)

Try it Yourself »

Example

The del keyword removes the item with the specified key name:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
del thisdict["model"]
print(thisdict)

Try it Yourself »

Example

The del keyword can also delete the dictionary completely:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
del thisdict
print(thisdict) #this will cause an error because "thisdict" no longer exists.

Try it Yourself »

Example

The clear() method empties the dictionary:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
thisdict.clear()
print(thisdict)

Try it Yourself »

Python – Loop Dictionaries

Copy a Dictionary

You cannot copy a dictionary simply by typing dict2 = dict1, because: dict2 will only be a reference to dict1, and changes made in dict1 will automatically also be made in dict2.

There are ways to make a copy, one way is to use the built-in Dictionary method copy().

Example

Make a copy of a dictionary with the copy() method:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
mydict = thisdict.copy()
print(mydict)

Try it Yourself »

Another way to make a copy is to use the built-in function dict().

Example

Make a copy of a dictionary with the dict() function:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
mydict = dict(thisdict)
print(mydict)

Python – Copy Dictionaries

Copy a Dictionary

You cannot copy a dictionary simply by typing dict2 = dict1, because: dict2 will only be a reference to dict1, and changes made in dict1 will automatically also be made in dict2.

There are ways to make a copy, one way is to use the built-in Dictionary method copy().

Example

Make a copy of a dictionary with the copy() method:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
mydict = thisdict.copy()
print(mydict)
Try it Yourself »

Another way to make a copy is to use the built-in function dict().

Example

Make a copy of a dictionary with the dict() function:

thisdict = {
"brand""Ford",
  "model""Mustang",
  "year"1964
}
mydict = dict(thisdict)
print(mydict)
Try it Yourself »
 

Python – Nested Dictionaries

Nested Dictionaries

A dictionary can contain dictionaries, this is called nested dictionaries.

Example

Create a dictionary that contain three dictionaries:

myfamily = {
  "child1" : {
    "name" : "Emil",
    "year" : 2004
  },
  "child2" : {
    "name" : "Tobias",
    "year" : 2007
  },
  "child3" : {
    "name" : "Linus",
    "year" : 2011
  }
}

Try it Yourself »

Or, if you want to add three dictionaries into a new dictionary:

Example

Create three dictionaries, then create one dictionary that will contain the other three dictionaries:

child1 = {
"name" : "Emil",
"year" : 2004
},
child2 = {
    "name" : "Tobias",
    "year" : 2007
  },
child3 = {
"name" : "Linus",
"year" : 2011
}

myfamily = {
  "child1" : child1,
  "child2" : child2,
  "child3" : child3
}

Python Dictionary Methods

Dictionary Methods

Python has a set of built-in methods that you can use on dictionaries.

MethodDescription
clear()Removes all the elements from the dictionary
copy()Returns a copy of the dictionary
fromkeys()Returns a dictionary with the specified keys and value
get()Returns the value of the specified key
items()Returns a list containing a tuple for each key value pair
keys()Returns a list containing the dictionary’s keys
pop()Removes the element with the specified key
popitem()Removes the last inserted key-value pair
setdefault()Returns the value of the specified key. If the key does not exist: insert the key, with the specified value
update()Updates the dictionary with the specified key-value pairs
values()Returns a list of all the values in the dictionary
 

Python Dictionary Exercises

Test Yourself With Exercises

Now you have learned a lot about dictionaries, and how to use them in Python.

Are you ready for a test?

Try to insert the missing part to make the code work as expected:


Test Yourself With Exercises

Exercise:

Use the get method to print the value of the “model” key of the car dictionary.

car =	{
  "brand""Ford",
  "model""Mustang",
  "year"1964
} print()

Start the Exercise

Go to the Exercise section and test all of our Python Dictionary Exercises:

Python Dictionary Exercises

Python 3.10.4

Python Modules

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