Python - functional "find"?

functional-programming, lambda, python

Solution

You can use `itertools.dropwhile` to skip over the items for which the supplied function returns `False`, then take the first item of the rest (if any). If you need the index rather than the item, incorporate `enumerate` from the Recipes section of `itertools` docs.

To reverse truth values returned by the supplied function, use a `lambda` (`lambda x: not pred (x)`, where `pred` is the supplied function) or a named wrapper:

def negate(f):
    def wrapped(x):
        return not f(x)
    return wrapped

Example:

def odd(x): return x % 2 == 1
itertools.dropwhile(negate(odd), [2,4,1]).next()
# => 1

This will throw `StopIteration` if no matching item is found; wrap it in a function of your own to throw an exception of your choice instead.

Problem

I need a function, which is capable of iterating over the collection, calling a supplied function with element of the collection as a parameter and returning the parameter or it's index when received "True" from supplied function. It is somethong like this: ``` def find(f, seq, index_only=True, item_only=False): """Return first item in sequence where f(item) == True.""" index = 0 for item in seq: if f(item): if index_only: return index if item_only: return item return index, item index+= 1 raise KeyError ``` So I am wondering whether there's anything like that in standart python toolset?

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