Python 3 basics

30 Jun, 2022
Python was developed by Guido van Rossum in the early 1990s and its latest version is 3.10.4, we can simply call it Python3. Python 3.0 was released in 2008. and is interpreted language i.e it’s not compiled and the interpreter will check the code line by line. This article can be used to learn the very basics of Python programming language. So before moving on further.. let’s do the most popular ‘HelloWorld’ tradition  and hence compare Python’s Syntax with C, C++, and Java ( I have taken these 3 because they are the most famous and mostly used languages). 
Python3
# Python code for "Hello World"# nothing else to type...see how simple is the syntax.  print("Hello World")      
Note: Please note that Python for its scope doesn’t depend on the braces ( { } ), instead it uses indentation for its scope. Let us start with our basics of Python where we will be covering the basics in some small sections. Just go through them and trust me you’ll learn the basics of Python very easily.
Introduction and Setup
If you are on Windows OS download Python by Clicking here and now install from the setup and in the start menu type IDLE.IDLE, you can think it as an Python’s IDE to run the Python Scripts. It will look somehow this : If you are on Linux/Unix-like just open the terminal and on 99% linux OS Python comes preinstalled with the OS.Just type ‘python3’ in terminal and you are ready to go. It will look like this : 
If you are on Windows OS download Python by Clicking here and now install from the setup and in the start menu type IDLE.IDLE, you can think it as an Python’s IDE to run the Python Scripts. It will look somehow this : 
If you are on Linux/Unix-like just open the terminal and on 99% linux OS Python comes preinstalled with the OS.Just type ‘python3’ in terminal and you are ready to go. It will look like this : 
The ” >>> ” represents the python shell and its ready to take python commands and code.
Variables and Data Structures
In other programming languages like C, C++, and Java, you will need to declare the type of variables but in Python you don’t need to do that. Just type in the variable and when values will be given to it, then it will automatically know whether the value given would be an int, float, or char or even a String.
Python3
# Python program to declare variablesmyNumber = 3print(myNumber)   myNumber2 = 4.5print(myNumber2)   myNumber ="helloworld"print(myNumber)
3
4.5
helloworld
See, how simple is it, just create a variable and assign it any value you want and then use the print function to print it. Python have 4 types of built in Data Structures namely List, Dictionary, Tuple and Set.
List is the most basic Data Structure in python. List is a mutable data structure i.e items can be added to list later after the list creation. It’s like you are going to shop at the local market and made a list of some items and later on you can add more and more items to the list.append() function is used to add data to the list. 
Python3
# Python program to illustrate a list    # creates a empty listnums = []    # appending data in listnums.append(21)nums.append(40.5)nums.append("String")   print(nums)
[21, 40.5, 'String']
Python3
# Python program to illustrate a Dictionary  # creates a empty listDict = []  # putting integer valuesDict = {1: 'Geeks', 2: 'For', 3: 'Geeks'}  print(Dict)  #Code submitted by Susobhan AKhuli
{1: 'Geeks', 2: 'For', 3: 'Geeks'}
Python3
# Python program to illustrate a tuple    # creates a tuple which is immutabletup = ('Geeks', 'For', 'Geeks')  print(tup)  #Code submitted by Susobhan AKhuli
('Geeks', 'For', 'Geeks')
Python3
# Python program to illustrate a set  # define a set and its elementsmyset = set(["Geeks", "For", "Geeks"])  #as set doesn't have duplicate elements so, 1 geeks will not be printedprint(myset)  #Code submitted by Susobhan Akhuli
Comments:
# is used for single line comment in Python
""" this is a comment """ is used for multi line comments
Input and Output
In this section, we will learn how to take input from the user and hence manipulate it or simply display it. input() function is used to take input from the user.
Python3
# Python program to illustrate# getting input from username = input("Enter your name: ")    # user entered the name 'harssh'print("hello", name)
Enter your name: hello harssh
Python3
# Python3 program to get input from user   # accepting integer from the user# the return type of input() function is string ,# so we need to convert the input to integernum1 = int(input("Enter num1: "))num2 = int(input("Enter num2: "))   num3 = num1 * num2print("Product is: ", num3)
Output:
Enter num1: 8 Enter num2: 6 ('Product is: ', 48)
Selection
Selection in Python is made using the two keywords ‘if’ and ‘elif’(elseif) and else
Python3
# Python program to illustrate# selection statement   num1 = 34if(num1>12):   print("Num1 is good")elif(num1>35):   print("Num2 is not gooooo....")else:   print("Num2 is great")
Num1 is good
Functions
You can think of functions like a bunch of code that is intended to do a particular task in the whole Python script. Python used the keyword ‘def’ to define a function.Syntax:
def function-name(arguments):
           #function body
Python3
# Python program to illustrate# functionsdef hello():   print("hello")   print("hello again")hello()   # calling functionhello()
hello
hello again
hello
hello again
Now as we know any program starts from a ‘main’ function...lets create a main function like in many other programming languages.
Python3
# Python program to illustrate # function with maindef getInteger():   result = int(input("Enter integer: "))   return result   def Main():   print("Started")      # calling the getInteger function and    # storing its returned value in the output variable   output = getInteger()        print(output)   # now we are required to tell Python # for 'Main' function existenceif __name__=="__main__":   Main()
Started
Enter integer: 0
Iteration (Looping)
As the name suggests it calls repeating things again and again. We will use the most popular ‘for and while’ loop here.
Python3
Python3
# Python program to illustrate# a simple for loop   for step in range(5):       print(step)
# Python program to illustrate# a simple while loopstep = 0while(step < 5):    print(step)    step = step+1
0
1
2
3
4
Modules
Python has a very rich module library that has several functions to do many tasks. You can read more about Python’s standard library by Clicking here‘import’ keyword is used to import a particular module into your python code. For instance consider the following program.
Python3
# Python program to illustrate# math moduleimport math   def Main():   num = -85      # fabs is used to get the absolute    # value of a decimal   num = math.fabs(num)   print(num)              if __name__=="__main__":   Main()
85.0
These are some of the most basics of the Python programming language and I will be covering both the intermediate and advanced level Python topics in my upcoming articles.
This article is contributed by Harsh Wardhan Chaudhary. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Your article will be reviewed first by Geeks for Geeks team before publishing.
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