Putting two keys with the same hash into a dict

Question

>>> one_decimal = Decimal('1')
>>> one_complex = complex(1,0)
>>> d = {one_decimal: '1D', one_complex: '1C'}
>>> len(d)
2
>>> map(hash, d)
[1, 1]

Above, I create a dict with a hash collision, and two slots occupied.

>>> d[1]
'1D'
>>> d[1+0j]
'1C'

How is that getitem handled for the integer 1? And how does the indexing manage to resolve the correct value for a complex literal indexing?

Python 2.7.12 / Linux.

Answer 1

As the accepted answer mentioned by @CoryKramer states, equality of hashes does not imply equality of objects. Python dictionaries can contain any number of elements with equal hashes as long as the objects themselves are not equal.

The short answer to your question is probably that the implementation of the complex type is a bit incomplete in the Python library as of 2.7. As @wim points out, comparing int and complex using == works fine, but comparing Decimal and complex does not. Since comparing one_decimal == one_complex will always return False because of their types, they can both live in the same dictionary in Python 2.7.

This issue has been fixed in Python 3. I am experimenting in 3.5, where one_decimal and one_complex are equal. After running the same snippet, the dictionary contains the value for one_complex under the key one_decimal, as expected (first key, last value).

TL;DR

It's a bug in Py2.7's complex type. Fixed in Py3.