From: Neil Cerutti <neilc@norwich.edu>
Newsgroups: comp.lang.python
Subject: Re: how to avoid leading white spaces
Date: 6 Jun 2011 16:08:05 GMT
Organization: Norwich University
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On 2011-06-06, rurpy@yahoo.com <rurpy@yahoo.com> wrote:
> On 06/03/2011 02:49 PM, Neil Cerutti wrote:
> Can you find an example or invent one? I simply don't remember
> such problems coming up, but I admit it's possible.
>
> Sure, the response to the OP of this thread.

Here's a recap, along with two candidate solutions, one based on
your recommendation, and one using str functions and slicing. 

(I fixed a specification problem in your original regex, as one
of the lines of data contained a space after the closing ',
making the $ inappropriate)

data.txt:
//ACCDJ         EXEC DB2UNLDC,DFLID=&DFLID,PARMLIB=&PARMLIB,
//         UNLDSYST=&UNLDSYST,DATABAS=MBQV1D0A,TABLE='ACCDJ       '
//ACCT          EXEC DB2UNLDC,DFLID=&DFLID,PARMLIB=&PARMLIB,
//         UNLDSYST=&UNLDSYST,DATABAS=MBQV1D0A,TABLE='ACCT        '
//ACCUM         EXEC DB2UNLDC,DFLID=&DFLID,PARMLIB=&PARMLIB,
//         UNLDSYST=&UNLDSYST,DATABAS=MBQV1D0A,TABLE='ACCUM       '
//ACCUM1        EXEC DB2UNLDC,DFLID=&DFLID,PARMLIB=&PARMLIB,
//         UNLDSYST=&UNLDSYST,DATABAS=MBQV1D0A,TABLE='ACCUM1      ' 
^Z

import re

print("re solution")
with open("data.txt") as f:
    for line in f:
        fixed = re.sub(r"(TABLE='\S+)\s+'", r"\1'", line)
        print(fixed, end='')

print("non-re solution")
with open("data.txt") as f:
    for line in f:
        i = line.find("TABLE='")
        if i != -1:
            begin = line.index("'", i) + 1
            end = line.index("'", begin)
            field = line[begin: end].rstrip()
            print(line[:i] + line[i:begin] + field + line[end:], end='')
        else:
            print(line, end='')

These two solutions print identical output processing the sample
data. Slight changes in the data would reveal divergence in the
assumptions each solution made.

I agree with you that this is a very tempting candidate for
re.sub, and if it probably would have been my first try as well.

-- 
Neil Cerutti