On 25 January 2013 01:11, Chris Angelico <ros...@gmail.com> wrote:
> On Fri, Jan 25, 2013 at 12:03 PM, Oscar Benjamin
> <oscar.j.benja...@gmail.com> wrote:
>> On 24 January 2013 11:35, Chris Angelico <ros...@gmail.com> wrote:
>>>
>>> It's usually fine to have int() complain about any non-numerics in the
>>> string, but I must confess, I do sometimes yearn for atoi() semantics:
>>> atoi("123asd") == 123, and atoi("qqq") == 0. I've not seen a
>>> convenient Python function for doing that. Usually it involves
>>> manually getting the digits off the front. All I want is to suppress
>>> the error on finding a non-digit. Oh well.
>>>
>>
>> I'm interested to know what the situations are where you want the
>> behaviour of atoi().
>
> It simplifies operations on strings that contain numbers. For
> instance, here's a problem from yesterday. I have a set of files (MIDI
> files of The Rose of Persia) which have been sloppily numbered:
>
> Rose_1.mid
> Rose_10.mid
> Rose_11.mid
> Rose_12.mid
> Rose_13.mid
> Rose_14.mid
> Rose_15.mid
> Rose_16.mid
> Rose_17.mid
> Rose_18.mid
> Rose_19.mid
> Rose_2.mid
> Rose_20.mid
> Rose_21.mid
> Rose_22.mid
> Rose_23.mid
> Rose_24.mid
> Rose_3.mid
> Rose_4.mid
> Rose_5.mid
> Rose_6.mid
> Rose_7.mid
> Rose_8.mid
> Rose_9.mid
> Rose_Int.mid
>
> They're not in order. The one marked "Int" is the Introduction and
> should be first; then Rose_1 ... Rose_9, then Rose_10 ... Rose_24. In
> fact, the correct sort order is exactly:
>
> atoi(filename[5:])
I have solved similar situations with
sorted(filenames, key=lambda s: (len(s), s))
which is better than lexicographical ordering for sorting integer
strings. It gets the _Int file wrong in this case (but I consider it
luck that atoi does what you want for that file).
Oscar
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