I found *.py{} in a .gitignore file and I am wondering what this extension is.
Found here.
And here.
PS. The git commit mentioned pypy.
It isn't a common file extension, but the braces {} are used in globs (like regex) for pattern recognition. From this link on globs, it is
Bash style brace expansions. This is applied to patterns before anything else.
Though it's left empty so I'm not sure that it does anything of use in this case.