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Re: Confusing math problem

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From Oscar Benjamin <oscar.j.benjamin@gmail.com>
Date Fri, 22 Feb 2013 00:04:30 +0000
Subject Re: Confusing math problem
To Schizoid Man <schiz_man@21stcentury.com>
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On 21 February 2013 23:41, Schizoid Man <schiz_man@21stcentury.com> wrote:
> "Oscar Benjamin" <oscar.j.benjamin@gmail.com> wrote in
>> Then you want operator.pow:
>>
>>>>> import operator
>>>>> operator.pow(3, 2)
>>
>> 9
>>
>> math.pow is basically the (double)pow(double, double) function from
>> the underlying C library. operator.pow(a, b) is precisely the same as
>> a**b.
>
> So how is operator.pow() different from just pow()?

operator.pow(a, b) calls a.__pow__(b). This is also what a**b does. If
a and b are ints then the __pow__ method will create the appropriate
int exactly without overflow and return it. You can make your own
class and give it a __pow__ function that does whatever you like:

>>> class Number(object):
...   def __pow__(self, other):
...     print('__pow__ called, returning 3')
...     return 3
...
>>> n = Number()
>>> result = n**3
__pow__ called, returning 3
>>> result
3

operator.pow will call the method:

>>> import operator
>>> operator.pow(n, 3)
__pow__ called, returning 3
3

math.pow will not:

>>> import math
>>> math.pow(n, 3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: a float is required

The math module essentially exposes the functions that would be
available in C after importing math.h. So when you call math.pow(a,
b), a and b are if possible converted to float (which corresponds to a
double in C) and then the result is computed and returned as a float.


Oscar

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Thread

Confusing math problem "Schizoid Man" <schiz_man@21stcentury.com> - 2013-02-21 19:33 +0000
  Re: Confusing math problem Dave Angel <davea@davea.name> - 2013-02-21 15:25 -0500
    Re: Confusing math problem "Schizoid Man" <schiz_man@21stcentury.com> - 2013-02-21 22:39 +0000
      Re: Confusing math problem Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-21 22:53 +0000
        Re: Confusing math problem "Schizoid Man" <schiz_man@21stcentury.com> - 2013-02-21 23:41 +0000
          Re: Confusing math problem Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-02-22 00:04 +0000
          Re: Confusing math problem Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-21 17:19 -0700
    Re: Confusing math problem "Schizoid Man" <schiz_man@21stcentury.com> - 2013-02-21 23:39 +0000
  Re: Confusing math problem Ian Kelly <ian.g.kelly@gmail.com> - 2013-02-21 13:42 -0700
  Re: Confusing math problem Chris Angelico <rosuav@gmail.com> - 2013-02-22 07:46 +1100
    Re: Confusing math problem "Schizoid Man" <schiz_man@21stcentury.com> - 2013-02-21 22:44 +0000
      Re: Confusing math problem Chris Angelico <rosuav@gmail.com> - 2013-02-22 11:29 +1100
      Re: Confusing math problem Dave Angel <davea@davea.name> - 2013-02-21 21:19 -0500
  Re: Confusing math problem Dave Angel <davea@davea.name> - 2013-02-21 15:49 -0500
  Re: Confusing math problem Chris Angelico <rosuav@gmail.com> - 2013-02-22 08:23 +1100
    Re: Confusing math problem Peter Pearson <ppearson@nowhere.invalid> - 2013-02-21 21:59 +0000
      Re: Confusing math problem Chris Angelico <rosuav@gmail.com> - 2013-02-22 09:11 +1100
      Re: Confusing math problem Dave Angel <davea@davea.name> - 2013-02-21 17:33 -0500
      Re: Confusing math problem Chris Angelico <rosuav@gmail.com> - 2013-02-22 10:15 +1100
    Re: Confusing math problem Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-22 09:16 +0000
      Re: Confusing math problem Serhiy Storchaka <storchaka@gmail.com> - 2013-02-22 13:48 +0200
  Re: Confusing math problem Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-02-22 09:27 +0000

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