Internal Iterators in Python

gistfile1.py

class Enumerable(object):
    def map(self, fn):
        acc = []
        self.each(lambda xs: acc.append(fn(xs)))
        return self.__class__(acc)
    
    collect = map
    
    def filter(self, pred):
        acc = []
        self.each(lambda xs: acc.append(xs) if pred(xs) else None)
        return self.__class__(acc)
    
    select = filter
    
    def reduce(self, reducer, init=None):
        s = object()
        acc = { "v": s if init is None else init }
        self.each(lambda xs: acc.__setitem__("v", xs) if acc["v"] is s else acc.__setitem__("v", reducer(acc["v"], xs)))
        return acc["v"]
    
    foldl = reduce
    
    def count(self):
        acc = { "v": 0 }
        self.each(lambda _: acc.__setitem__("v", acc["v"]+1))
        return acc["v"]
    
    size = count

    
class MyList(Enumerable, list):
    def each(self, fn):
        for e in self:
            fn(e)
        return self

    
class MyDict(Enumerable, dict):
    def each(self, fn):
        for item in self.iteritems():
            fn(item)
        return self
    
    
d = MyDict({"a": 1, "b": 2})
l = MyList([1, 2, 3, 4])

print d.filter(lambda (k, v): v % 2 == 0).map(lambda (k, v): (k, v ** 2))
print l.filter(lambda e: e % 2 == 0).map(lambda e: e ** 2).foldl(lambda a, b: a + b, 20)