Question

I’m currently building a tool that will have to match filenames against a pattern. For convenience, I intend to provide both lazy matching (in a glob-like fashion) and regexp matching. For example, the following two snippets would eventually have the same effects:

@mylib.rule('static/*.html')
def myfunc():
    pass

@mylib.rule(r'^static/([^/]+)\.html')
def myfunc():
    pass

AFAIK r'' is only useful to the Python parser and it actually creates a standard str instance after parsing (the only difference being that it keeps the \).

Is anybody aware of a way to tell one from another?

I would hate to have to provide two alternate decorators for the same purpose or, worse, resorting manually parsing the string to determine if it’s a regexp or not.

Answer 1

You can’t tell them apart. Every raw string literal could also be written as a standard string literal (possibly requiring more quoting) and vice versa. Apart from this, I’d definitely give different names to the two decorators. They don’t do the same things, they do different things.

Example (CPython):

>>> a = r'^static/([^/]+)\.html'; b = '^static/([^/]+)\.html'
>>> a is b
True

So in this particular example, the raw string literal and the standard string literal even result in the same string object.