Question

class Number(object):
    def __init__(self):
        super(Number, self).__init__()
        self.data = 10

    def __getattr__(self, name):
        def _missing(*args, **kwargs):
            method = getattr(self.data, name)
            return method(args[0])

        return _missing

a = Number()
b = Number()

print a.__add__(10)   # this is ok!
print a + 10          # TypeError: "unsupported operand type(s) for +: 'Number' and 'int'"
print a + b           # TypeError: "unsupported operand type(s) for +: 'Number' and 'Number'"

Question:
What’s the difference between “a.__add__(10)” and “a + 10”, How can I hook the operator “+” ?

Answer 1

Python will only use an actual __add__ method, not one that only “exists” due to __getattr__.

When adding __add__ = (10).__add__ it works fine.

So what you’ll want to do is adding proxy methods:

def __add__(self, *args): return self.data.__add__(*args)
def __sub__(self, *args): return self.data.__sub__(*args)
# ...