Python list comprehension - want to avoid repeated evaluation

Question

I have a list comprehension which approximates to:

[f(x) for x in l if f(x)]

Where l is a list and f(x) is an expensive function which retu

Answer 1

You should use a memoize decorator. Here is an interesting link.

---

Using memoization from the link and your 'code':

def memoize(f):
    """ Memoization decorator for functions taking one or more arguments. """
    class memodict(dict):
        def __init__(self, f):
            self.f = f
        def __call__(self, *args):
            return self[args]
        def __missing__(self, key):
            ret = self[key] = self.f(*key)
            return ret
    return memodict(f)

@memoize
def f(x):
    # your code

[f(x) for x in l if f(x)]