opps, forgot to include my test code -- could be handy:
On Fri, Dec 27, 2019 at 11:52 PM Christopher Barker <python...@gmail.com>
wrote:
> On Fri, Dec 27, 2019 at 5:39 PM Guido van Rossum <gu...@python.org> wrote:
>
>> Is duck typing float or Decimal worth the bother? Barring that it could
>> be done with some isinstance() checks (in the user code, not in
>> math.isnan()).
>>
>
> well, for the topic at hand in another thread -- in the statistics module.
> And I was coming to the same conclusion, but it dawned on me that another
> option would be to add a .is_nan() method to floats. (same as Decimal). It
> would be a lighter-weight option that a new dunder, but accomplish a
> similar effect -- anyone implementing a new numeric type that support NaN
> could add that method.
>
> BTW, could you simply do:
>
> def is_nan(num):
> try:
> return num.is_nan()
> except AttributeError:
> if isinstance(num, complex):
> return cmath.isnan(num)
> try:
> return math.isnan(num)
> except:
> return False
>
> I don't like the bare except, but it may be OK to say that anything that
> can't be coerced to a float is not a NaN. (na you could trap the exeptions
> we expect anyway)
>
> And this doesn't require you to import the Decimal module, and you can
> document that it will work with any type that either has an is_nan()
> method, or can have its NaN values successfully coerced into a float.
>
> And we could remove the complex support -- does the rest of the statistics
> module support it anyway? But it did make me think -- what if the complex
> number __float__() would work for NaN, and Inf, and -inf -- then you could
> have a single isnan() implementation in the math module,
>
> (in fact, that could be a standard part of the __float__ protocol)
>
>
> By the way:
>
> ----> 1 float(Decimal('snan'))
> ValueError: cannot convert signaling NaN to float
>
> Why can't it convert a signaling NaN to a float? Isn't a signaling NaN
> part of the IEE 754 spec?
>
> -CHB
>
> --
> Christopher Barker, PhD
>
> Python Language Consulting
> - Teaching
> - Scientific Software Development
> - Desktop GUI and Web Development
> - wxPython, numpy, scipy, Cython
>
--
Christopher Barker, PhD
Python Language Consulting
- Teaching
- Scientific Software Development
- Desktop GUI and Web Development
- wxPython, numpy, scipy, Cython
"""
some tests of an is_nan function
"""
import math
import cmath
from decimal import Decimal
from fractions import Fraction
import numpy as np
import pytest
def is_nan(num):
try:
return num.is_nan()
except AttributeError:
if isinstance(num, complex):
return cmath.isnan(num)
try:
return math.isnan(num)
except:
return False
nan_vals = [Decimal('nan'),
Decimal('snan'),
float('nan'),
np.nan,
np.array(np.nan, dtype=np.float128),
complex(float('nan'), 1),
complex(0, float('nan')),
complex(float('nan'), float('nan')),
]
non_nan_vals = [34,
10**1000, # an int too big for a float
3.4,
np.array(1e200, dtype=np.float128) * 1e200, # a numpy float128 too big for a float
Decimal('1e500'),
Fraction(1,10),
Fraction(1,1000000)**100, # fraction too small for a float
Fraction(10,1) ** 500, # fraction too large for a float
complex(1, 2),
complex(-123, 154),
]
@pytest.mark.parametrize("num", nan_vals)
def test_nan(num):
assert is_nan(num)
@pytest.mark.parametrize("num", non_nan_vals)
def test_not_nan(num):
assert not is_nan(num)
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