question of style

[Lie Ryan]

Paul Rubin wrote:
> Generally, having a special
> value like None to denote a missing datum was considered standard
> practice a few decades ago, 

I guess in python, None as the missing datum idiom is still quite prevalent:

def cat_list(a=None, b=None):
    # poor man's list concatenation
    if a is None and b is None: return []
    if a is None: return b
    if b is None: return a
    return a + b