refactoring can change the value of strings (fstring formatting)

[ReinhardtJ]

Issue description or question

I'm currently writing a parser for a certain file format by using regexes. This is my code

tag_pattern = r':([0-9]{2}[A-Z]):'
qualifier_pattern = r':([A-Z]{4})\/\/'
tag_and_qualifier_pattern = f'{tag_pattern}{qualifier_pattern}'

on the line with qualifier_pattern, it suggests me

• Inline variable that is only used once(inline-variable)
• Simplify unnecessary nesting, casting and constant values in f-strings(simplify-fstring-formatting)

As soon as I apply, the code becomes

tag_pattern = r':([0-9]{2}[A-Z]):'
tag_and_qualifier_pattern = f'{tag_pattern}:([A-Z]{4})\\/\\/'

Firstly, the curly braces around the 4 won't appear in the string anymore, secondly, it adds additional escape-backslashes in front of the already existing backslashes (probably beacuse it detects that qualifier_pattern is an r-string. I usually use r-strings for regex-patterns to prevent accidental string formatting, even if it is not needed in this example. Ideally, it shouldn't matter of course).

Sourcery Version

0.10.1.

Code editor or IDE name and version

Pycharm 2021.3.1

OS name and version

Windows

[Hellebore]

Thanks for raising - have reproduced the issue and will look into a fix.