start of an iterable:

    >>> iterable = (None, False, None, 1, 2, None, 3, False, None)
    >>> pred = lambda x: x in {None, False, ''}
    >>> list(lstrip(iterable, pred))
    [1, 2, None, 3, False, None]

This function is analogous to to :func:`str.lstrip`, and is essentially
an wrapper for :func:`itertools.dropwhile`.

)