(original) (raw)

Math.pow() predates ** by many releases.

On Sunday, October 21, 2012, Steven D'Aprano wrote:

On 21/10/12 21:11, Antoine Pitrou wrote:

On Sun, 21 Oct 2012 13:38:48 +1100
Chris Angelico<rosuav@gmail.com> �wrote:

On Sun, Oct 21, 2012 at 12:53 PM, Steven D'Aprano<steve@pearwood.info> �wrote:

Python 2.x legitimately distinguished between floats and complex, e.g.:

py> �(-100.0)\*\*0.5

Traceback (most recent call last):
� �File "", line 1, in
ValueError: negative number cannot be raised to a fractional power

If you wanted a complex result, you can explicitly ask for one:

py> �(-100.0+0j)\*\*0.5
(6.123031769111886e-16+10j)


I see that behaviour is changed in Python 3.

Python 2 (future directives aside) also required you to explicitly ask
for floating point. That was also changed in Python 3\. That doesn't
mean that this is necessarily the right thing to do, but it does have
precedent. The square root of a negative number is by nature a complex
number.

In the set of complex numbers, it is. But in the set of float numbers,
a negative number has no square root. I think Steven may be worried
about the impact on people who don't know about complex numbers, which
is a reasonable concern.

Precisely.

I'm also not sure why we have several variants of the power operator:
\*\*, built-in pow(), math.pow().

In Python 3.3, math.pow is the builtin pow. Presumably for backwards
compatibility reasons when they were different? If so, it was a LONG
time ago:

\[steve@ando \~\]$ python1.5
Python 1.5.2 (#1, Aug 27 2012, 09:09:18) �\[GCC 4.1.2 20080704 (Red Hat 4.1.2-52)\] on linux2
Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam

import math

math.pow

And yet strangely there's never been a cmath.pow.



\--
Steven
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