even exponentiation of negative numbers

[benlbroussard]

BPO	6781
Nosy	@mdickinson

^{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 2009-08-25.12:35:08.482>
created_at = <Date 2009-08-25.12:29:23.867>
labels = ['invalid']
title = 'even exponentiation of negative numbers'
updated_at = <Date 2009-08-25.13:03:52.914>
user = 'https://bugs.python.org/benlbroussard'

bugs.python.org fields:

activity = <Date 2009-08-25.13:03:52.914>
actor = 'mark.dickinson'
assignee = 'none'
closed = True
closed_date = <Date 2009-08-25.12:35:08.482>
closer = 'mark.dickinson'
components = ['None']
creation = <Date 2009-08-25.12:29:23.867>
creator = 'benlbroussard'
dependencies = []
files = []
hgrepos = []
issue_num = 6781
keywords = []
message_count = 3.0
messages = ['91951', '91952', '91953']
nosy_count = 2.0
nosy_names = ['mark.dickinson', 'benlbroussard']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue6781'
versions = ['Python 2.6']

[benlbroussard]

Negative one squared should be one, but is negative one sometimes.

pow(-1, 2) = 1
-1 ** 2 = -1
-1 ^ 2 = -1

The ** and ^ operators aren't working like expected, and the pow()
documentation is incorrect since it says "The two-argument form pow(x,
y) is equivalent to using the power operator: x**y."

[mdickinson]

This is not a bug:

-1 ** 2 is parsed as -(1 ** 2), not (-1) ** 2. Take a look at:

http://docs.python.org/reference/expressions.html#the-power-operator

In -1 ^ 2, ^ is the bitwise exclusive-or operator, not the power operator.

pow(x, y) is indeed equivalent to x**y:

Python 2.6.2 (r262:71600, Aug 22 2009, 17:53:25) 
[GCC 4.0.1 (Apple Inc. build 5493)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> x = -1
>>> y = 2
>>> x ** y
1
>>> pow(x, y)
1
>>>

[mdickinson]

By the way, I get -1 ^ 2 == -3, not -1:

>>> -1 ^ 2
-3

If you're getting -1 instead, then that *is* a bug! Are you?