def iterate(func, start):
    """Return ``start``, ``func(start)``, ``func(func(start))``, ...

        >>> from itertools import islice
        >>> list(islice(iterate(lambda x: 2*x, 1), 10))
        [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]

    """
    while True:
        yield start
        start = func(start)
