Serhiy Storchaka <storchaka+cpyt...@gmail.com> added the comment:
If you want to replace %d with literal \d, you need to repeat the backslash 4
times:
pattern = re.sub('%d', '\\\\d+', pattern)
or use a raw string literal and repeat the backslash 2 times:
pattern = re.sub('%d', r'\\d+', pattern)
Since the backslash has a special meaning in the replacement pattern, it needs
to be escaped with a backslash, i.e. duplicated. But since it has a special
meaning in Python string literals, every of these backslashes needs to be
escaped with a backslash in a non-raw string literal, i.e. repeated 4 times.
Python 3.6 is more lenient. It keeps a backslash if it is followed by a
character which doesn't compound a known escape sequences in a replacement
string. But it emits a deprecation warning, which you can see when run Python
with corresponding -W option.
$ python3.6 -Wa -c 'import re; print(re.sub("%d", "\d+", "DBMS_NAME: string(%d)
%s"))'
<string>:1: DeprecationWarning: invalid escape sequence \d
/usr/lib/python3.6/re.py:191: DeprecationWarning: bad escape \d
return _compile(pattern, flags).sub(repl, string, count)
DBMS_NAME: string(\d+) %s
$ python3.6 -Wa -c 'import re; print(re.sub("%d", "\\d+", "DBMS_NAME:
string(%d) %s"))'
/usr/lib/python3.6/re.py:191: DeprecationWarning: bad escape \d
return _compile(pattern, flags).sub(repl, string, count)
DBMS_NAME: string(\d+) %s
$ python3.6 -Wa -c 'import re; print(re.sub("%d", "\\\d+", "DBMS_NAME:
string(%d) %s"))'
<string>:1: DeprecationWarning: invalid escape sequence \d
DBMS_NAME: string(\d+) %s
$ python3.6 -Wa -c 'import re; print(re.sub("%d", "\\\\d+", "DBMS_NAME:
string(%d) %s"))'
DBMS_NAME: string(\d+) %s
Here "invalid escape sequence \d" is generated by the Python parser, "bad
escape \d" is generated by the RE engine.
----------
nosy: +serhiy.storchaka
resolution: -> not a bug
stage: -> resolved
status: open -> closed
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue34304>
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