[Python] Wrong input for python regex

[Freymaurer]

Using Regex.Match(..,..) in dotnet, it gets transpiled to the following in fable_library/reg_exp.py:

def match(reg: Pattern[str] | str, input: str, start_at: int = 0) -> Match[str] | None:
    if isinstance(reg, str):
        flags = _options_to_flags(start_at)
        return re.search(input, reg, flags)
    return reg.search(input, pos=start_at)

But re.search get its arguments in the order of: pattern, input... . So pattern and input are switched, which crashes obviously all matches.

😅

[Freymaurer]

Okay, that was not the error, as the match() function also has their arguments switched. So two false make a positive in this case. Propably best to update the argument naming.

[dbrattli]

@Freymaurer What F# code would crash on all matches? I'm not sure I understand how you trigged an error here. The code is obviously wrong, but I don't think it's ever used, ref: 7f494c4#diff-d143e99366f0ba295fb8bbc80bca86f86884323796fb2da0e473e8a8dcf7eeb0

[Freymaurer]

Hey! The issue actually was us not checking for python regex dialect.

But when we lloked at the source code in python we saw that "input und pattern" are switched between re.search and the match function. Thats why we thought there is a bug in the source code. But the match function was also given input and pattern switched so "two false make a right" everything is working correctly, just the function arguments have the wrong names.

[Freymaurer]

I hope i was able to explain the issue @dbrattli 😅 Everything works as intended, but the argument names of match are wrong

[dbrattli]

Are you sure? How do you see they are wrong? I tried:

let regex = Regex("pattern")
let mat = regex.Match("input")

This transpiles to:

regex: Any = create("pattern")
mat: Any = match(regex, "input")

So the pattern is the first argument and input text is the second which seems right?

[Freymaurer]

Have a look at the image from my original post, there it says:

return re.search(input, reg, flags)

With reg being defined as Pattern in the match function. But intellisense in re.search expects the arguments in the order of:

Pattern -> string -> FlagsType

But according to the match arguments we give it in the order of:

string -> Pattern -> FlagsType

[dbrattli]

Yes, my question was how did you trigger that part of the code to run? I'm not sure it's even used since it's been removed in the TypeScript specific part of Fable. There looks to be no unit-test that hits that code. So just want to check with you how/if you manged to call that code-line. If not, I will just remove the code.

[Freymaurer]

A sorry i must have misunderstood!

Here is a REPL of a minimal example.

[dbrattli]

Thanks, now I see the problem. Making a fix for this ...