[Python-Dev] Symmetry arguments for API expansion

[Serhiy Storchaka]

12.03.18 21:15, Guido van Rossum пише:
> There's a reason why adding this to int feels right to me. In mypy we 
> treat int as a sub*type* of float, even though technically it isn't a 
> sub*class*.. The absence of an is_integer() method on int means that 
> this code has a bug that mypy doesn't catch:
> 
> def f(x: float):
>      if x.is_integer():
>          "do something"
>      else:
>          "do something else"

What is the real use case of float.is_integer()?

I searched on GitHub and found only misuses of it like 
(x/5).is_integer() (x % 5 == 0 would be more correct and clear) or 
(x**0.5).is_integer() (returns wrong result for large ints and some 
floats) in short examples. Some of these snippets look like book 
examples, and they propagate bad practices (like "if a.is_integer() == 
True:").