Numeric types in Python have the interesting property that their hash() is often their value:
>>> hash(1)
1
>>> hash(1.0)
1
Python also considers floating point and integers of the same value to be equal:
>>> 1 == 1.0
True
Two things with the same hash that are equal count as the same key in a dict:
>>> 1 in {1.0: 'cat'}
True
However, it is possible for the key to be either an int or a float:
>>> {1: 'first'}
{1: 'first'}
>>> {1.0: 'second'}
{1.0: 'second'}
Whichever key is used first sticks. Later writes to the dict can change the value, but the int or float key remains:
>>> {1: 'first', 1.0: 'second'}
{1: 'second'}
>>> {1.0: 'first', 1: 'second'}
{1.0: 'second'}
