Variable assignment in python: behind the scenes

Python variable assignment is different from some of the popular languages like c, c++ and java. There is no declaration of a variable in python just an assignment statement.

Let us see why?

When we declare a variable in C or similar languages. The declaration statement sets aside an area of memory for holding values allowed by the data type of the declared variable. The memory allocated will be interpreted as the data type suggests. If it’s an integer variable the memory allocated will be read as an integer and so on. When we assign or initialize it with some value, the value will get stored at that memory location. At compile time the initial value or assigned value will be matched with the allowed values for that data type. So we cannot mix types. Example: initializing a string value to an int variable is not allowed, and the program will not compile.

On the contrary, Python is a dynamically typed language. It doesn’t know about the type of the variable until the code is run. So declaration is of no use. What it does is, It stores that value at some memory location and then binds that variable name to that memory container. And makes the contents of the container accessible through that variable name. So the data type does not matter. As it will get to know the type of the value at run-time. And it is the programmer’s responsibility to ensure that the operands used, support the operations.

# This will store 6 in the memory and binds the# name x to it. After it runs, type of x will# be int.

x = 6

print(type(x))

# This will store 'hello' at some location in# the memory and binds name x to it. After it# runs type of x will be str.

x = 'hello'

print(type(x))

Output:

<class 'int'> 
<class 'str'>

Originally published at www.geeksforgeeks.org on September 15, 2018.