** operator does not overflow to inf

[KeithRandall]

BPO	20543
Nosy	@mdickinson, @iritkatriel
Superseder	bpo-3222: inf*inf gives inf, but inf**2 gives overflow error

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-11-07.09:55:52.712>
created_at = <Date 2014-02-07.18:44:35.603>
labels = ['interpreter-core', 'type-bug']
title = '** operator does not overflow to inf'
updated_at = <Date 2020-11-07.09:55:52.711>
user = 'https://bugs.python.org/KeithRandall'

bugs.python.org fields:

activity = <Date 2020-11-07.09:55:52.711>
actor = 'mark.dickinson'
assignee = 'none'
closed = True
closed_date = <Date 2020-11-07.09:55:52.712>
closer = 'mark.dickinson'
components = ['Interpreter Core']
creation = <Date 2014-02-07.18:44:35.603>
creator = 'Keith.Randall'
dependencies = []
files = []
hgrepos = []
issue_num = 20543
keywords = []
message_count = 7.0
messages = ['210517', '210523', '210525', '210526', '210527', '380490', '380497']
nosy_count = 3.0
nosy_names = ['mark.dickinson', 'Keith.Randall', 'iritkatriel']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '3222'
type = 'behavior'
url = 'https://bugs.python.org/issue20543'
versions = ['Python 3.2']

[KeithRandall]

>>> 1e200*1e200
inf
>>> 1e200**2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: (34, 'Numerical result out of range')

Shouldn't floating-point operations overflow to inf, not generate exceptions?

[mdickinson]

Shouldn't floating-point operations overflow to inf, not generate exceptions?

This has been discussed a few times before (I'll try to find the references).

But to answer you question: actually, no. I think they *should* generate exceptions. That is, if I were to change anything here, it would be the result of the multiplication, not the result of the ** operation. IMO, numerically naive users shouldn't be exposed to infinities and NaNs; they should get exceptions for invalid inputs instead. The math and cmath modules fairly rigorously follow this idea, but as you've discovered the built-in operators aren't so consistent.

Fixing it without breaking existing code and without annoying existing users is tricky, though.

[mdickinson]

Issue bpo-3222 is related.

[mdickinson]

And here's a link to the middle of a related discussion under the heading "Turn off ZeroDivisionError?" on python-list, Feb 2008.

https://mail.python.org/pipermail/python-list/2008-February/473302.html

You'd have to read up- and down-thread to get the entire discussion.

[mdickinson]

See also bpo-18570.

[iritkatriel]

If there are no objections, I will close this as a duplicate of bpo-3222.

[mdickinson]

Thanks, @iritkatriel. Sounds good to me.