mutable and inmutable in python.txt

Introduction
You have been hearing about mutable and immutable all along. Simply put, objects which can be modified after creation in the same memory location are called mutable and the others which cannot are termed immutable.

Immutable Objects: int, float, long, complex, string, tuple, bool

Mutable Objects: list, dict, set, byte array, user-defined classes

Checking Mutability
You can check if an object is mutable by first modifying the object and then comparing its new memory location with the old memory location. You can check for memory location either by using the id() function, which gives the memory location of an object or with the help of is operator, which checks for the identity of two objects.

First, let's take an integer (type int) 50 and add 1 to it with the same variable name, then check its memory location before and after modification with id(). As it turns out, both have different memory locations, and hence it is an immutable type.

#initial variable
a = 50
# initial memory location
print(id(a))
#modified variable
a += 1
# new memory location, is it same?
print(id(a))
Output

94285850046496
94285850046528
Now, let's take a list with values [1,2,3,4] and add 5 to it with .append(). You observe that after modification, it still refers to the same memory location as before and hence it is of mutable type.

# intial list 
l = [1,2,3,4]
# initial memory location
print(id(l))
print('='*20)
# new list
l.append(5)
print(l)
print('='*20)
# new memory location
print(id(l))
Output

139678448773256
====================
[1, 2, 3, 4, 5]
====================
139678448773256