Lisp mentality vs. Python mentality

Arnaud Delobelle arnodel at googlemail.com
Sun Apr 26 15:08:49 CEST 2009


bearophileHUGS at lycos.com writes:

> You can also use quite less code, but this is less efficient:
>
> def equal_items(iter1, iter2, key=lambda x: x):
>     class Guard(object): pass
>     try:
>         for x, y in izip_longest(iter1, iter2, fillvalue=Guard()):
>             if key(x) != key(y):
>                 return False
>     except TypeError: # intercepts key(guard)
>         return False
>     return True

You don't want to silence TypeErrors that may arise from with key() when
x or y is not a Guard, as it could hide bugs in key(). So I would write
something like this:

def equal_items(iter1, iter2, key=lambda x: x, _fill = object()):
    for x, y in izip_longest(iter1, iter2, fillvalue=_fill):
        if x is _fill or y is _fill or key(x) != key(y):
            return False
    return True

(untested)

Another way would be:

def equal_items(iter1, iter2, key=lambda x: x):
    iter1, iter2 = iter(iter1), iter(iter2)
    for x, y in izip(iter1, iter2):
        if key(x) != key(y):
            return False
    for x, y in izip_longest(iter1, iter2):
        return False
    return True

(untested)

-- 
Arnaud



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