I started learning python back in 2017 and since then I am still learning it and using it and almost everyday I write some python code. Python is an interpreter based language, you can write the code directly in the interpreter or in a separate file(extension is .py) and run it.
Using the interpreter
Fire up your terminal and type
python3. And you will see something like this below code snippet.
$ python3 Python 3.6.8 (default, Jan 14 2019, 11:02:34) [GCC 8.0.1 20180414 (experimental) [trunk revision 259383]] on linux Type "help", "copyright", "credits" or "license" for more information. >>>
Now we are going to print “Hello World!” using the interpreter.
>>> print("Hello World!") Hello World!
Using a source file
Create a file called
helloWorld.py and enter the following text:
We can run this file by
$ python3 helloWorld.py Hello World!
Whitespaces and indentation
Language like c/c++ use pair of curly brackets to divide different identifiers. In the python it uses indentation for that. The whitespaces at the beginning of the line is known as indentation. If you give wrong whitespaces then it will give you errors. Python use 4 whitespaces for a single indentation. Below there is an example.
>>> a = "Aniruddha" >>> b = "Basak" File "<stdin>", line 1 b = "Basak" ^ IndentationError: unexpected indent
Comment is a line in python that will start with # and the interpreter of python will just ignores the lines. You can write anything here to describe your code.
>>> # This is a comment >>> # The next line will multiply two numbers >>> a = 12 * 34 >>> print(a) # Printing the value of a
If your description is long then it is recommended that you use multiline comments. There is two options for that.
# This is option 1 # Multiline comment
""" This is option 2 Multiline comment """
The reason why python is loved by so many people is it gives so many modules to work on almost everything you can imagine. Basically modules are python files that contains different functions classes and variable that you can reuse.
>>> import os >>> print(os.name) posix
Keywords and Identifiers
Below the following identifiers are main keywords of python. They must exactly types as it is.
False class finally is return None continue for lambda try True def from nonlocal while and del global not with as elif if or yield assert else import pass break except in raise
Variables and Datatypes
In python we don’t specify the type of the variable while declaring it.If we declare
a = 1 then a will become an integer type and if we define
b = "Hii" then b will become an string type variable.
>>> a = "Hi " >>> b = "how you doing?" >>> a + b 'Hi how you doing?'
Taking input from keyboard
We can take input from users while executing the program. We can use the
input() function given by python for this. Let’s see an example of taking input from user.
number = int(input("Enter number: ")) print(number)
Here is the result –
$ python3 input.py Enter number: 25 25
Operators and Expressions
Python language supports the following types of operators.
- Arithmetic Operators
- Comparison (Relational) Operators
- Assignment Operators
- Logical Operators
- Bitwise Operators
- Membership Operators
- Identity Operators
It is used to perform common mathematical operations.
>>> a = 2 >>> b = 4 >>> a + b 6 >>> a - b -2 >>> a * b 8 >>> a / b 0.5 >>> a % b 2 >>> a ** b 16 >>> a // b 0
It is used for comparing two values and returns either
>>> a = 2 >>> b = 4 >>> a == b False >>> a != b True >>> a > b False >>> a < b True >>> a >= b False >>> a <= b True
This operator is used to assign values to some variable.
>>> x = 5 >>> x += 5 >>> x -= 5 >>> x *= 5 >>> x /= 5
Logical operators are the
>>> x = True >>> y = False >>> print('x and y is ', x and y) x and y is False >>> print('x or y is', x or y) x or y is True >>> print('not x is', not x) not x is False
Bitwise operator works on bits and performs bit by bit operation. Assume if
a = 60 and
b = 13. Now in binary format they will be as follows –
>>> a = 60 >>> b = 30 >>> a & b 28 >>> a | b 62 >>> a ^ b 34 >>> ~a -61 >>> a >> 2 15 >>> a << 2 240
Python’s membership operators test for membership in a sequence, such as strings, lists, or tuples. There are two membership operators as explained below −
a = 'Hello World' print('H' in a)
Identity operators compare the memory locations of two objects. There are two Identity operators explained below −
>>> a = 5 >>> b = 5 >>> c = 10 >>> print(a is not b) False >>> print(a is b) True >>> print(a is c) False