On Thu, 27 Aug 2009 23:05:41 +0000, Kreso wrote:
> I am writing an application that essentially calculates set of numbers,
> say N1, N2, ..., where they can be calculated by several different
> algorithms. (One should be able to choose the algorithm at run time.) In
> each algorithm one starts from a set of functions, say f1, f2, ...,
> which are then transformed into some other functions g1(f1, f2, ..),
> g2(f1, f2, ...), ... , then maybe transformed once more and result is
> obtained by evaluating final functions.
Sounds like you're doing functional programming. There's a rich set of
functional tools in languages like Haskell, but in Python there's only a
few, such as partial(). (See the functools module.)
However, you can make your own, using the following general technique.
Suppose you want to compose two functions, f and g. Then with a helper
function:
def compose(f, g):
def composed_function(*args):
return f(g(*args))
return composed_function
you can do this:
>>> def add1(x):
... return x+1
...
>>> def double(y):
... return 2*y
...
>>> double_plus_one = compose(add1, double)
>>> double_plus_one(3.5)
8.0
Unfortunately, about the only thing you can't do is check the return type
of functions without actually calling them.
> I can naturally think about this as a collection of transformation
> blocks, which have functions as input and output, and which can be put
> together to get the final results. However, I am not sure how to program
> this, especially since one cannot subclass function type. To be clear
> let me give simplified example of what is needed:
>
> f(x) has unknown shape, so one would like to try, say
>
> f1(x) = ax - b x**2 or f2(x) = a sin(b*x),
>
> where a and b are variable parameters.
You need factory functions!
def axbx2_factory(a, b):
# Return a function that returns a*x-b*x**2
def inner(x):
return a*x -b*x**2
return inner
And in use:
>>> f1 = axbx2_factory(1, 2)
>>> f2 = axbx2_factory(1, 0)
>>> f1(2.5)
-10.0
>>> f1(3.5)
-21.0
>>> f2(2.5)
2.5
>>> f2(3.5)
3.5
Hope this helps.
--
Steven
--
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