# Mutability

An object is considered mutable if if can be changed after it is created, whereas it is immutable if it can not be changed. If you change a mutable object all references to that object will also be changed.

In Python Index , lists, sets and dictionaries are mutable whereas numbers, strings, tuples and frozen sets are immutable.

This is commonly used in interview questions, for example:

a = [0,0]
b = [a,a]
a[1] = 1
print(b) # [ [0,1], [0,1] ]

whereas

a = (0,0)
b = (a,a)
a[1] = 1 # TypeError: 'tuple' object does not support item assignment

though read more about this in Mutability in Python .