def keep(f, seq=EMPTY):
    """Maps seq with f and iterates truthy results.
       Simply iterates truthy values in one argument version."""
    if seq is EMPTY:
        return _filter(bool, f)
    else:
        return _filter(bool, map(f, seq))
Maps seq with f and iterates truthy results.
       Simply iterates truthy values in one argument version.
funcy/seqs.py