Lazy array

lazyarray.py

class LazyArray(object):
    """
    Wraps an iterable object and provides lazy array functionality,
    namely, lazy index access and iteration. Lazily got iteration
    results are cached and reused to provide consistent view
    for users.
    """

    def __init__(self, iterable_source):
        self.source = iterable_source
        self.got_elements = []
        self.read_count = 0

    def __iter__(self):
        # yield cached result
        for elem in self.got_elements:
            yield elem
        # get results from iterable object
        for elem in self.source:
            self.read_count = self.read_count + 1
            self.got_elements.append(elem)
            yield elem

    def __getitem__(self, idx):
        # if element corresponds to specified index is not available,
        # get lacking results from iterable object
        from itertools import islice
        needed_read_count = max(idx - self.read_count + 1, 0)
        for elem in islice(self.source, 0, needed_read_count):
            self.read_count = self.read_count + 1
            self.got_elements.append(elem)
        return self.got_elements[idx]

if __name__ == "__main__":
    def getnumbers(n):
        for x in xrange(1, n):
            print("yield " + str(x))
            yield x
    larray = LazyArray(getnumbers(20))
    print("larray[7]: %d" % larray[7])
    for idx, x in enumerate(larray):
        print("larray[%d]: %d" % (idx, x))
    print("larray[10]: %d" % larray[10])