Ezio Melotti <ezio.melo...@gmail.com> added the comment:
I'm assuming you want to replace double backslashes with single backslashes in
stringy_thing, so I defined stringy_thingy and tried both your snippets but
they are both failing:
>>> stringy_thingy = r'foo\\bar\\baz'
>>> print(stringy_thingy) # stringy_thingy contains double backslashes
foo\\bar\\baz
>>> re.sub(r'\\\\', chr(92), stringy_thingy) # fails
Traceback (most recent call last):
...
File "/usr/lib/python3.6/sre_parse.py", line 245, in __next
self.string, len(self.string) - 1) from None
sre_constants.error: bad escape (end of pattern) at position 0
>>>
>>> parser = re.compile(r'\\\\')
>>> parser.sub(chr(92), stringy_thingy) # also fails
Traceback (most recent call last):
...
File "/usr/lib/python3.6/sre_parse.py", line 245, in __next
self.string, len(self.string) - 1) from None
sre_constants.error: bad escape (end of pattern) at position 0
Replacing chr(92) with r'\\' works for both:
>>> print(re.sub(r'\\\\', r'\\', stringy_thingy))
foo\bar\baz
>>> print(parser.sub(r'\\', stringy_thingy))
foo\bar\baz
The docs[0] says: "repl can be a string or a function; if it is a string, any
backslash escapes in it are processed."
So passing chr(92) (or '\\', which is equivalent) result in the above error
("bad escape (end of pattern)") because it's seen as an incomplete escape
sequence. Passing r'\\' seems to work as intended.
ISTM there is no bug and re.sub works as documented. Can you provide a
stringy_thingy for which the first of your snippet fails but the second
succeeds?
[0]: https://docs.python.org/3/library/re.html#re.sub
----------
resolution: -> not a bug
stage: -> test needed
status: open -> pending
type: -> behavior
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue35072>
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