Deleting specific characters from a string

[Bengt Richter]

On Thu, 10 Jul 2003 08:56:14 +0200, Behrang Dadsetan <ben at dadsetan.com> wrote:

>Bengt Richter wrote:
>> On Wed, 09 Jul 2003 23:36:03 +0200, Behrang Dadsetan <ben at dadsetan.com> wrote:
>> ====< removechars.py >========================================================
>> def removeChars(s, remove=''):
>>     return s.translate(
>>         '\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f'
>>         '\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f'
>>         ' !"#$%&\'()*+,-./'
>>         '0123456789:;<=>?'
>>         '@ABCDEFGHIJKLMNO'
>>         'PQRSTUVWXYZ[\\]^_'
>>         '`abcdefghijklmno'
>>         'pqrstuvwxyz{|}~\x7f'
>>         '\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f'
>>         '\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f'
>>         '\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf'
>>         '\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf'
>>         '\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf'
>>         '\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf'
>>         '\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef'
>>         '\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff'
>>         , remove)
><snip>
>It looks to me like serious overkill. If I would put in a method like 
>that somewhere in my code, my colleagues would never talk to me again ;)
>
What looks like overkill? The 256-character string literal? It is easy to explain,
and if you want utility functions like this, you can put them in a module and
your colleagues may never see beyond the import statement and the calls, unless
they are interested. It should have a doc-string though, which could advise using
help(str.translate) for further info ;-)

Note that the code for removeChars is not much to execute (29 bytecode bytes?), since the constant
is pre-defined (and the 9 bytes for SET_LINENOs could be optimized out):

>>> dis.dis(removeChars)
          0 SET_LINENO               1

          3 SET_LINENO               2
          6 LOAD_FAST                0 (s)
          9 LOAD_ATTR                1 (translate)
         12 LOAD_CONST               1 ('\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\
x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !"#$%&\'()*+,-./0123456789:;
<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f\x80\x81\x82\x83\x84\x85
\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d
\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5
\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd
\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5
\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd
\xfe\xff')

         15 SET_LINENO              19
         18 LOAD_FAST                1 (remove)
         21 CALL_FUNCTION            2
         24 RETURN_VALUE
         25 LOAD_CONST               0 (None)
         28 RETURN_VALUE

(I believe the last two codes are never executed, just vestigial code-generation by-product
for the case of non-explicit returns at the end).

If you want to get rid of the extras, you can do python -OO and use lambda to get rid of
the vestigial return code:

 >>> removeChars = lambda s, remove='': s.translate(
 ...         '\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f'
   <snip>
 ...         '\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff'
 ...         , remove)
 >>>

Gets you:

 >>> import dis
 >>> dis.dis(removeChars)
           0 LOAD_FAST                0 (s)
           3 LOAD_ATTR                1 (translate)
           6 LOAD_CONST               1 ('\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\
 x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !"#$%&\'()*+,-./0123456789:;
   <snip>
 \xfe\xff')
           9 LOAD_FAST                1 (remove)
          12 CALL_FUNCTION            2
          15 RETURN_VALUE 

What do you mean by overkill? ;-)

Regards,
Bengt Richter