[Tutor] Advise...

[Danny Yoo]

> > There has been alot of talk on this list about using list comprehensions
> > lately, and this could be one of those useful places.  While I don't
> > have time to experiment with real code, I would suggest changing your
> > function to look like:
> >
> > steps = [ min_x + i*delta_x for i in range(steps) ]
> > totalarea = sum([ eval(func_x)*delta_x for x in steps ])
>
> Calling eval() there in the inner loop might be costly, because Python
> needs to do extra work to tokenize and parse the string, every time
> through the iteration.  We want to reduce the work done in tight inner
> loops like that.
>
> We can do some of that work up front by compiling the code.  Here's some
> hacky code to do the compilation up front:
>
> ###
> >>> def makeFunction(expressionString):
> ...     compiledExp = compile(expressionString, 'makeFunction', 'eval')
> ...     def f(x):
> ...         return eval(compiledExp, {}, {'x' : x})
> ...     return f
> ...
> ###


Oh!  There's a slightly simpler way to write that makeFunction():

###
>>> def makeFunction(s):
...     return eval("lambda x: " + s)
...
###



It even has a little less overhead than the previous code.


###
>>> timeIt(myFunctionOriginal)
0.035856008529663086
>>>
>>> timeIt(makeFunction("3*x*x"))
0.00087714195251464844
###



Best of wishes!