Monte Milanuk, 25.02.2010 18:27:
> So... pow(4,4) is equivalent to 4**4, which works on anything - integers,
> floats, etc.
Correct, e.g.
>>> class Test(object):
... def __pow__(self, other, modulo=None):
... print("POW!")
... return 'tutu'
...
>>> pow(Test(), 4)
POW!
'tutu'
>>> Test() ** 4
POW!
'tutu'
But:
>>> pow(Test(), 4, 5)
POW!
'tutu'
The pow() function has a 3-argument form that efficiently calculates the
modulo. There is no operator for that, and, IMHO, that's the raison d'être
for the pow() function in the first place.
> but math.pow(4,4) only works on floats... and in this case it
> converts or interprets (4,4) as (4.0,4.0), hence returning a float: 256.0.
> Is that about right?
Yes. Read the docs:
"""
10.2. math — Mathematical functions
This module is always available. It provides access to the mathematical
functions defined by the C standard.
[...]
The following functions are provided by this module. Except when explicitly
noted otherwise, all return values are floats.
"""
http://docs.python.org/library/math.html
So these are purely numeric and therefore actually pretty fast functions,
which is /their/ raison d'être.
$ python3.1 -m timeit -s 'from math import pow as mpow' 'pow(2,2)'
1000000 loops, best of 3: 0.562 usec per loop
$ python3.1 -m timeit -s 'from math import pow as mpow' 'mpow(2,2)'
10000000 loops, best of 3: 0.18 usec per loop
However:
$ python3.1 -m timeit -s 'from math import pow as mpow' '2**2'
10000000 loops, best of 3: 0.0247 usec per loop
Stefan
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
