Re: Is there any way to say ignore case with "in"?

On Apr 6, 8:53 am, "Martin v. Löwis" <mar...@xxxxxxxxxxx> wrote:
I know I could use:-

    if lower(string1) in lower(string2):
        <do something>

but it somehow feels there ought to be an easier (tidier?) way.

Easier?  You mean like some kind of mind meld?

Interestingly enough, it shouldn't be (but apparently is) obvious that

   a.lower() in b.lower()

is a way of expressing "a is a substring of b, with case-insensitive
matching". Can we be sure that these are really the same concepts,
and if so, is

  a.upper() in b.upper()

also equivalent?

It's probably a common assumption that, for any character c,
c.lower()==c.upper().lower(). Yet,

py> [i for i in range(65536) if unichr(i).upper().lower() !=
unichr(i).lower()]
[181, 305, 383, 837, 962, 976, 977, 981, 982, 1008, 1009, 1010, 1013,
7835, 8126]

Take, for example, U+017F, LATIN SMALL LETTER LONG S. It's .lower() is
the same character, as the character is already in lower case.
It's .upper() is U+0053, LATIN CAPITAL LETTER S. Notice that the LONG
is gone - there is no upper-case version of a "long s".
It's .upper().lower() is U+0073, LATIN SMALL LETTER S.

So should case-insensitive matching match the small s with the small
long s, as they have the same upper-case letter?

Regards,
Martin

Another surprise (or maybe not so surprising) - this "upper != lower"
is not symmetric. Using the inverse of your list comp, I get

[i for i in range(65536) if unichr(i).lower().upper() !=
... unichr(i).upper()]
[304, 1012, 8486, 8490, 8491]

Instead of 15 exceptions to the rule, conversion to upper has only 5
exceptions. So perhaps comparsion of upper's is, while not foolproof,
less likely to encounter these exceptions? Or at least, simpler to
code explicit tests.

-- Paul
.

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