Python id() built-in function
From the Python 3 documentation
Return the “identity” of an object. This is an integer which is guaranteed to be unique and constant for this object during its lifetime. Two objects with non-overlapping lifetimes may have the same id() value.
Introduction
The id() function returns a unique integer that identifies an object in memory. This ID is guaranteed to be unique for the lifetime of the object. It’s essentially the memory address of the object.
Examples
x = 10
y = 10
z = 20
print(id(x)) # Output might be something like 4331368528
print(id(y)) # Output will be the same as id(x) because Python caches small integers
print(id(z)) # Output will be different
print(id(1))
print(id('1'))
print(id([1, 2]))