Currently a raw literal cannot end in a single backslash (e.g. in
r"C:\User\"). Although there are reasons for this. It is an old gotcha,
and there are many closed issues about it. This question is even
included in FAQ.
The most common workarounds are:
r"C:\User" "\\"
and
r"C:\User\ "[:-1]
I tried to experiment. It was easy to make the parser allowing a
trailing backslash character. It was more difficult to change the Python
implementation in the tokenizer module. But this change breaks existing
code in more sites than I expected. 14 Python files in the stdlib (not
counting tokenizer.py) will need to be fixed. In all cases it is a
regular expression.
Few examples:
1.
r"([\"\\])"
If only one type of quotes is used in a string, we can just use
different kind of quotes for creating a string literal and remove escaping.
r'(["\\])'
2.
r'(\'[^\']*\'|"[^"]*"|...'
If different types o quotes are used in different parts of a string, we
can use implicit concatenation of string literals created with different
quotes (in any case a regular expression is long and should be split on
several lines on semantic boundaries).
r"('[^']*'|"
r'"[^"]*"|'
r'...'
3.
r"([^.'\"\\#]\b|^)"
You can also use triple quotes if the string contain both type of quotes
together.
r"""([^.'"\\#]\b|^)"""
4. In rare cases a multiline raw string literals can contain both `'''`
and `"""`. In this case you can use implicit concatenation of string
literals created with different triple quotes.
See https://github.com/python/cpython/pull/15217 .
I do not think we are ready for such breaking change. It will break more
code than forbidding unrecognized escape sequences, and the required
fixes are less trivial.
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