RegexUrlResolver's _get_reverse_dict appends objects of unknown type to the reverse dict

[fas]

In _get_reverse_dict:

if isinstance(pattern, RegexURLResolver):
    # ...
else:
    bits = normalize(p_pattern)
    self._reverse_dict.appendlist(pattern.callback, (bits, p_pattern))
    self._reverse_dict.appendlist(pattern.name, (bits, p_pattern))

In the else branch it is implicitly assumed that pattern is of type RegexURLPattern (it uses its properties). This does not have to be the case. For example, one could create a different kind of RegexURLResolver which does not inherit RegexURLResolver. This resolver would be handled as a RegexURLPattern instance and added to the reverse dict.
Patch is a short one: replace "else" with "elif isinstance(pattern, RegexURLPattern):".

[Alex Gaynor]

Why? What's the usecase here?

[Malcolm Tredinnick]

Whilst supporting more generic URL resolving classes is a goal, I don't think this is the solution. We need to fix the reversing support to allow handing off to lower-level classes in those cases and this means coming up with an internal interface protocol for what they need to support (probably just a reverse method, but it needs a bit of planning). So I'm going to wontfix this particular item and then in the 1.2 timeframe or thereabouts, we can work out a general plan for this. The current ticket and patch assume a solution, rather than necessarily fleshing out that it's solving the right problem and I think the problem is a little broader than that.