[New-bugs-announce] [issue47121] math.isfinite() can raise exception when called on a number

Thomas Fischbacher report at bugs.python.org
Fri Mar 25 13:28:43 EDT 2022

New submission from Thomas Fischbacher <tfish at google.com>:

>>> help(math.isfinite)
isfinite(x, /)
    Return True if x is neither an infinity nor a NaN, and False otherwise.

So, one would expect the following expression to return `True` or `False`. We instead observe:

>>> math.isfinite(10**1000)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: int too large to convert to float

(There likewise is a corresponding issue with other, similar, functions).

This especially hurts since PEP-484 states that having a Sequence[float] `xs` does not allow us to infer that `all(issubclass(type(x), float) for x in xs)` actually holds - since a PEP-484 "float" actually does also include "int" (and still, issubclass(int, float) == False).

Now, strictly speaking, `help(math)` states that

    This module provides access to the mathematical functions
    defined by the C standard.

...but according to "man 3 isfinite", the math.h "isfinite" is a macro and not a function - and the man page does not show type information for that reason.

messages: 416010
nosy: tfish2
priority: normal
severity: normal
status: open
title: math.isfinite() can raise exception when called on a number

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