On Sep 28, 5:12 pm, Hrvoje Niksic <[EMAIL PROTECTED]> wrote:
> xkenneth <[EMAIL PROTECTED]> writes:
> > Looking to do something similair. I'm working with alot of timestamps
> > and if they're within a couple seconds I need them to be indexed and
> > removed from a list.
> > Is there any possible way to index with a custom cmp() function?
>
> > I assume it would be something like...
>
> > list.index(something,mycmp)
>
> The obvious option is reimplementing the functionality of index as an
> explicit loop, such as:
>
> def myindex(lst, something, mycmp):
> for i, el in enumerate(lst):
> if mycmp(el, something) == 0:
> return i
> raise ValueError("element not in list")
>
> Looping in Python is slower than looping in C, but since you're
> calling a Python function per element anyway, the loop overhead might
> be negligible.
>
> A more imaginative way is to take advantage of the fact that index
> uses the '==' operator to look for the item. You can create an object
> whose == operator calls your comparison function and use that object
> as the argument to list.index:
>
> class Cmp(object):
> def __init__(self, item, cmpfun):
> self.item = item
> self.cmpfun = cmpfun
> def __eq__(self, other):
> return self.cmpfun(self.item, other) == 0
>
> # list.index(Cmp(something, mycmp))
>
> For example:
>
> >>> def mycmp(s1, s2):
>
> ... return cmp(s1.tolower(), s2.tolower())>>> ['foo', 'bar',
> 'baz'].index(Cmp('bar', mycmp))
> 1
> >>> ['foo', 'bar', 'baz'].index(Cmp('Bar', mycmp))
> 1
> >>> ['foo', 'bar', 'baz'].index(Cmp('nosuchelement', mycmp))
>
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> ValueError: list.index(x): x not in list
>
> The timeit module shows, somewhat surprisingly, that the first method
> is ~1.5 times faster, even for larger lists.
Hrvoje,
That's fun! thx.
--Alan
the cut-n-paste version /w minor fix to 'lower'.
# ----------------------------------------------
class Cmp(object):
def __init__(self, item, cmpfun):
self.item = item
self.cmpfun = cmpfun
def __eq__(self, other):
return self.cmpfun(self.item, other) == 0
def mycmp(s1, s2):
return cmp(s1.lower(), s2.lower())
print ['foo', 'bar', 'baz'].index(Cmp('bar', mycmp))
print ['foo', 'bar', 'baz'].index(Cmp('Bar', mycmp))
try:
print ['foo', 'bar', 'baz'].index(Cmp('nosuchelement', mycmp))
except ValueError:
print "Search String not found!"
# end example
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