Using the LALR file cache on Python 2.7 fails with "unbound method exists() must be called with FS instance as first argument (got str instance instead)"

I’m using Lark for epycc https://github.com/antoniotejada/epycc on Python 2.7 and I found that when using the LALR with cache=True:

parser = lark.Lark.open(grammar_filepath, keep_all_tokens="True", 
    lexer="standard", parser="lalr", cache=True)

fails with

Exception has occurred: TypeError
unbound method exists() must be called with FS instance as first argument (got str instance instead)
        File "C:\Python27\Lib\site-packages\lark\lark.py", line 276, in __init__
        if FS.exists(cache_fn):
        File "C:\Python27\Lib\site-packages\lark\lark.py", line 501, in open
        return cls(f, **options)
                ...

The problem is in utils.FS that doesn’t declare “exists” as @staticmethod the same way it’s done for “open”

An easy workaround is:

setattr(lark.utils.FS, 'exists', staticmethod(os.path.exists))
parser = lark.Lark.open(grammar_filepath, keep_all_tokens="True", 
    lexer="standard", parser="lalr", cache=True)

[MegaIng]

but I’m having fun with my custom lexer

That is reason enough. Otherwise, you would probably be using pycparser

Also note that you could alternatively add it as a requirement for the suffix to have the next character not be alphanumeric.

Also, you are the third person in the last few days to come across that issue. I think I am going to provide a PR.

(return as identifier for a call vs return as a statement is something that could also be fixed by priorities. Also, adding a negative look ahead will certainly be faster than whatever else you can do in pure python, but might create large problems with the rest of lark.)

Edit: The suffix problem is solvable by just moving the longest option first. Use INT_SIZE_SUFFIX: "ll" | "LL" |"l" | "L" instead.

[erezsh]

Thanks for the catch. We’ll merge the fix soon.

Just curious, in what context are you using Lark with Python 2.7?

I ask because we are planning to drop support for Python 2 soon.