Python Variables | Rules and Conventions

Variables are used in programs to store and compute your desired data. To declare variables in Python '=' is used. It is also used to assign some value to it. Unlike languages like C, C++ , JAVA where each name is "declared" in advance with its type. In Python variable type is not fixed. Variables inherit their type from their current value.

Note: Although it is not a good programming practise to assign values of mixed types to same variable. It can lead to errors in program logic. To find the type of a variable or expression use type(e). type(e) returns the data type of expression or variable name passed as parameter.

Let's look at few examples below:

num = 1

Num = 3

Name = "Henry"

X = 8.5

Let's see how they print:

Python variables - declaration and prinitng

Key Points:

num = 1 is also known as assignment statement. Left hand side is a variable name and right hand side is an expression.
Variable names are case-sensitive. You can clearly see that when we try to print 'x' there is an error showing that it is not defined. Hence 'x' and 'X' are two different variables.
There is no need to specify the type of value that the variable will hold.
Numeric values can be int or float ( Integers or fractional numbers). 145, -3,471456123 are values of type int. no fractional no decimals.
float having fractional or decimals.0.6, 0.3334333, 5.5
For an int, this sequence is read off as a binary number. int value is stored in one single cell. Int had values where decimal is fixed or no decimal.
For a float, this sequence breaks up into a mantissa and exponent. float values are stored in two part one for mantissa and exponent.
0.602 x 10²⁴
0.602 is mantissa and 10²⁴ is exponent.
For add, sub and multiplications, if (add or sub or multi) to int number you get int and two float then you get float.
Division will always produce a float. 7/3.5 is 2.0. 7/2 is 3.5.
Python allows mix of int and float. Such as 8 + 2.5 = 10.5. Output will be float.