Bugs related to NumPy's new __numpy_ufunc__ hook.

test_power.py

import numpy as np


class buggy(object):

    def __init__(self, arr):
        self.arr = arr

    def __pow__(self, other):
        print "In __pow__"
        return self.arr ** other

    def __rpow__(self, other):
        print "In __rpow__"
        return other ** self.arr

    def __ipow__(self, other):
        print "In __ipow__"
        self.arr **= other
        return self

    def __add__(self, other):
        print "In __add__"
        return self.arr + other

    def __radd__(self, other):
        print "In __radd__"
        return other + self.arr

    def __iadd__(self, other):
        print "In __iadd__"
        self.arr += other
        return self

    def __numpy_ufunc__(self, ufunc, method, i, inputs, **kwargs):
        print "In __numpy_ufunc__"


a = np.arange(1, 6)
g = buggy(np.arange(2, 7))
print 'DOING __iadd__'
g += a
print g.arr

a = np.arange(1, 6)
g = buggy(np.arange(2, 7))
print 'DOING reversed __iadd__'
a += g
print a

a = np.arange(1, 6)
g = buggy(np.arange(2, 7))
print 'DOING __ipow__'
g **= a
print g.arr

a = np.arange(1, 6)
g = buggy(np.arange(2, 7))
print 'DOING reversed __ipow__'
a **= g

I believe this is an unrelated sidenote and probably expected behavior. However, because it throws a similar error I'm pointing it out here.

I noticed that when the __numpy_ufunc__ is not present in the buggy class, line 48 (a += g) fails with:

Traceback (most recent call last):
  File "test.py", line 48, in <module>
    a += g
TypeError: ufunc 'add' output (typecode 'O') could not be coerced to provided output parameter (typecode 'l') according to the casting rule ''same_kind''

I suppose this is expected behavior because __numpy_ufunc__ indicates to NumPy that it should be able to handle this type of object. That is, when __numpy_ufunc__ is not present it throws this error.