[Tutor] Testing Membership in a Sequence

[Karl Pflästerer]

Christian Wyglendowski <- Christian.Wyglendowski at greenville.edu wrote:

> What I am actually trying to do is look for command line options in
> sys.argv.

> if '-o' in sys.argv or '--option' in sys.argv:
>     apply_option()


You could either use the optparse module or subclass the list class and
define a custom __contains__ method.

class MList (list):
    def __contains__(self, seq):
        try:
            for e in seq:
                if list.__contains__(self, e): return True
            return False
        except TypeError:
            return list.__contains__(self, seq)


For two options it may be a bit overkill but for a larger list it can be
convenient.

Here's an example:

In [42]: lst = MList(range(10))

In [43]: lst
Out[43]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

In [44]: 3 in lst
Out[44]: True

In [45]: (3, 11, 9) in lst
Out[45]: True

In [46]: (11, 20, -1) in lst
Out[46]: False


So you could write:

if ('-o', '--option) in MList(sys.argv): ...


   Karl
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