Optimizing Inner Loop Copy

[danielx]

Mark E. Fenner wrote:
> Mark E. Fenner wrote:
>
> > John Machin wrote:
> >
> >>
> >> Mark E. Fenner wrote:
> >>
> >>> Here's my class of the objects being copied:
> >>
> >> Here's a couple of things that might help speed up your __init__
> >> method, and hence your copy method:
> >>
> >>>
> >>> class Rule(list):
> >>>     def __init__(self, lhs=None, rhs=None, nClasses=0, nCases=0):
> >>
> >>     def __init__(self, lhs=None, rhs=(), nClasses=0, nCases=0):
> >>
> >>>         self.nClasses = nClasses
> >>>         self.nCases = nCases
> >>>
> >>>         if lhs is not None:
> >>>             self.extend(lhs)
> >> what does the extend method do? If it is small, perhaps inline a copy
> >> of its code here.
> >>>
> >>>         if rhs is None:
> >>>             self.rhs=tuple()
> >>>         else:
> >>>             self.rhs=rhs
> >>
> >> Replace the above 4 lines by:
> >>     self.rhs = rhs
> >>
> >> HTH,
> >> John
> >
> > John,
> >
> > Thanks.  I thought of those at the same you did!  I also incorporated one
> > other use of the default=() + no conditional:
> >
> > class Rule(list):
> >     def __init__(self, lhs=(), rhs=(), nClasses=0, nCases=0):
> >         self.nClasses = nClasses
> >         self.nCases = nCases
> >         self.extend(lhs) # note, self is a list so this is list.extend
> >         self.rhs=rhs
> >
> >     def copy(self):
> >         return Rule(self,
> >                     self.rhs,
> >                     self.nClasses,
> >                     self.nCases)
>
>
> Actually, I also removed the "passthrough" that copy was doing and just
> called the constructor directly.  So, at the top level code, we have:
>
> allNew = []
> for params in cases:
>     # newobj = initialObject.copy()
>     newObj = Rule(initialObject, initialObject.rhs,
>                   initialObject.nClasses,
>                   initialObject.nCases)
>     newObj.modify(params)
>     allNew.append(newObj)
> return allNew
>
> Regards,
> Mark

I'm not sure how much this will help, but another thing you can do is
put this line before the "for":

append = allNew.append

Then, replace the last line in the loop with

append(newObj)

Check out this doc for more info on optimizing Python, and the section
which talks about eliminating dots:

http://wiki.python.org/moin/PythonSpeed/PerformanceTips
http://wiki.python.org/moin/PythonSpeed/PerformanceTips#head-aa6c07c46a630a2fa10bd6502510e532806f1f62