feature request: a better str.endswith

[Bob Gailer]

At 05:01 AM 7/18/2003 -0700, Michele Simionato wrote:

>I often feel the need to extend  the string method ".endswith" to tuple
>arguments, in such a way to automatically check for multiple endings.
>For instance, here is a typical use case:
>
>if filename.endswith(('.jpg','.jpeg','.gif','.png')):
>     print "This is a valid image file"
>
>Currently this is not valid Python and I must use the ugly
>
>if filename.endswith('.jpg') or filename.endswith('.jpeg') \
>    or filename.endswith('.gif') or filename.endswith('.png'):
>     print "This is a valid image file"
>
>Of course a direct implementation is quite easy:
>
>import sys
>
>class Str(str):
>     def endswith(self,suffix,start=0,end=sys.maxint):#not sure about 
> sys.maxint
>         endswith=super(Str,self).endswith
>         if isinstance(suffix,tuple):
>             return sum([endswith(s,start,end) for s in suffix]) # multi-or
>         return endswith(suffix,start,end)
>
>if Str(filename).endswith(('.jpg','.jpeg','.gif','.png')):
>     print "This is a valid image file"
>
>nevertheless I think this kind of checking is quite common and it would be
>worth to have it in standard Python.
>
>Any reaction, comment ?

One of my favorite languages is APL. All APL variables are arrays of 0 or 
more dimensions, and most of the operations in APL take arrays as arguments 
and return arrays as results. So I am often frustrated in Python when I 
have to write a construct such as your example, when, IMHO, it would be 
easy to extend Python to accept sequences as arguments where only single 
values are currently allowed. One example is providing a sequence of 
integers to index another sequence, vis. given seq = [3, 5, 7, 1 ,4], 
seq[(1,3, 0)] would produce [5, 1, 3]. Currently the tersest way to do this 
is [seq[x] for x in (1,3,0)]. The new extension would probably execute 
faster, and is more readable. There are probably more situations that could 
also benefit from such an extension. I know that I can create some of these 
using magic methods, but how much nicer if they were native.

In APL one can specify indexes for the various dimensions of an array. If B 
is a rank 2 array, B[1 2;3 4] retrieves columns 3 and 4 of rows 1 and 2. 
WIBNI one could in a similar way drill into a nested list. I know the 
various importable array modules do some of these tings, but they are 
limited to homogeneous data.

Bob Gailer
bgailer at alum.rpi.edu
303 442 2625
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