[New-bugs-announce] [issue46173] float(x) with large x not raise OverflowError

[Cyker Way]

New submission from Cyker Way <cykerway at gmail.com>:

Acccording to: https://docs.python.org/3/library/functions.html#float

>    If the argument is outside the range of a Python float, an OverflowError will be raised.

It is well known that the maximum value in IEEE 754 binary64 format is:

    >>> M = ((1<<53)-1)<<(1023-52)
    ...

So `(M+1)` will be out of range. But `float(M+1)` gives me:

    >>> float(M+1)
    1.7976931348623157e+308

No OverflowError is thrown. Contrast this with:

    >>> float(M+M)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    OverflowError: int too large to convert to float

In another text: https://docs.python.org/3/tutorial/floatingpoint.html#representation-error

>   ...Almost all machines today (November 2000) use IEEE-754 floating point arithmetic, and almost all platforms map Python floats to IEEE-754 “double precision”...

Is Python not following IEEE 754 binary64 format or something missing here?

----------
components: Interpreter Core
messages: 409143
nosy: cykerway
priority: normal
severity: normal
status: open
title: float(x) with large x not raise OverflowError
type: behavior
versions: Python 3.10, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue46173>
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