I noticed a rather strange behaviour for integers, which doesn't apply, for example, to floats or decimals:
In [205]: 10.__add__
File "<ipython-input-205-24ed61a2ee18>", line 1
10.__add__
^
SyntaxError: invalid syntax
This does not happen for floats or decimals:
In [211]: Decimal(10).__add__
Out[211]: <bound method Decimal.__add__ of Decimal('10')>
In [204]: 10.3.__add__
Out[204]: <method-wrapper '__add__' of float object at 0x7fb48c60f840>