[Tutor] regexp

[Dinara Vakhitova]

Thank you for your answer, Steven.

Of course it would have been easier to write this function,
but unfortunately my task is to do it with a regular expression :(

D.

2011/11/5 Steven D'Aprano <steve at pearwood.info>

> Dinara Vakhitova wrote:
>
>> Hello,
>>
>> I need to find the words in a corpus, which letters are in the
>> alphabetical
>> order ("almost", "my" etc.)
>>
>
> Quoting Jamie Zawinski:
>
>    Some people, when confronted with a problem, think "I know, I'll
>    use regular expressions." Now they have two problems.
>
> Now you have two problems: find words in the corpus which are in
> alphabetical order, and get the damn regular expression to work correctly.
>
> Don't use a regex for this. It is much simpler to write a Python function
> to solve it:
>
> def letters_in_order(astring):
>    """Return True if letters in astring are in alphabetical order.
>
>    >>> letters_in_order("almost")
>    True
>    >>> letters_in_order("zoology")
>    False
>
>    """
>    if len(astring) <= 1:
>        return True
>    for i in range(1, len(astring)):
>        if astring[i] < astring[i-1]:
>           # Pair of characters are out of order.
>            return False
>    # If none of the pairs are out of order, they whole string
>    # must be in order.
>    return True
>
> words = filter(letters_in_order, corpus)
> for word in words:
>    print(word)
>
>
>
> --
> Steven
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-- 
*Yours faithfully,
Dinara Vakhitova*
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