isclose behavior on non-finite complex values seems incorrect

For example:

np.isclose(complex(float('inf'), 0), complex(float('inf'), 0))
: False

np.isclose(complex(1, float('inf')), complex(1, float('nan')), equal_nan=True)
: True

In the first case it seems like the same number should be close to itself, and in the latter case I think the numbers should not be close since NaN is not close to anything.

Python’s cmath.isclose behavior appears to demand that complex numbers containing -inf or inf must be identical to be close. It does not support equal_nan so complex numbers containing NaN are never close to other complex numbers. If equal_nan is True I would expect NaNs to act like infinities and require the numbers be identical to be “close.”

[anirudh2290]

np.isclose(np.array([1 + 2.j]), np.array([2 + 1.j]))

I assume you forgot to replace some number with inf here? The issue is about inf/nan, and I don’t see anything wrong here with the given code snippet.

😄 sorry, my bad.

yes for inf it looks like it will be a breaking change, though i find the following behavior inconsistent in numpy:

>>> np.isclose(np.inf, np.inf)
True
>>> np.isclose(np.inf + 1.j, np.inf + 1.j)
False

[seberg]

Oh, I had forgotten after all this discussion that the original issue post already mentioned cmath and this behaviour. We need to decide what we think is best, and then open a bpo and maybe document the differences. I personally think the python behaviour with partial complex inf may just be an oversight (although python is in slightly different situations about giving warnings)?