simplest way to strip a comment from the end of a line?

[Arnaud Delobelle]

Joe Strout <joe at strout.net> writes:

> I have lines in a config file which can end with a comment (delimited
> by # as in Python), but which may also contain string literals
> (delimited by double quotes).  A comment delimiter within a string
> literal doesn't count.  Is there any easy way to strip off such a
> comment, or do I need to use a loop to find each # and then count the
> quotation marks to its left?
>
> Thanks,
> - Joe

FWIW this is what comes to mind.

>>> def strip_comment(line):
...     i = -1
...     while True:
...         i = line.find('#', i+1)
...         if i == -1:
...             return line
...         if line.count('"', 0, i) % 2 == 0:
...             return line[:i]
... 
>>> strip_comment('foo=1 # set foo')
'foo=1 '
>>> strip_comment('foo="bar" # set foo')
'foo="bar" '
>>> strip_comment('foo="bar # set foo"')
'foo="bar # set foo"'
>>> strip_comment('foo="bar # set foo" # set foo')
'foo="bar # set foo" '
>>> strip_comment('foo="bar # set foo" + "baz ## fubar" # set foo')
'foo="bar # set foo" + "baz ## fubar" '
>>> strip_comment('foo="bar # set foo" + "baz ## fubar # set foo"')
'foo="bar # set foo" + "baz ## fubar # set foo"'
>>> strip_comment(r'foo="bar\" baz" # this breaks')
'foo="bar\\" baz" # this breaks'

As the last example shows, it won't work if there is an escaped double
quote in the string.

-- 
Arnaud