flatten a list

flatten.py

def flatten(seq):
    l = []
    for elt in seq:
        t = type(elt)
        if t is tuple or t is list:
            for elt2 in flatten(elt):
                l.append(elt2)
        else:
            l.append(elt)
    return l

tkinter 的做法

def _flatten(seq):
    """Internal function."""
    res = ()
    for item in seq:
        if isinstance(item, (tuple, list)):
            res = res + _flatten(item)
        elif item is not None:
            res = res + (item,)
    return **res**