'if' v.s. `while` to a `functools.partial.func`

Question

In Django documentation django.conf.urls | Django documentation | Django

There's such codes:

class RegexURLPattern(LocaleRegexProvider):
    ...
    def lookup_str(self)
        callback = self.callback
        # Python 3.5 collapses nested partials, so can change "while" to "if"
        # when it's the minimum supported version.
        while isinstance(callback, functools.partial):
            callback = callback.func
        ...

The code is to callback the argument of funtion 'view' and execute it.

Why while is better than if excluding 'Python 3.5'? There is only one callback argument passed in from django.conf.urls.url,which seen in:

def url(regex, view, kwargs=None, name=None):
    elif callable(view):
        return RegexURLPattern(regex, view, kwargs, name)

It seems if is more readable than while.

Answer 1

It's not about number of arguments but about the depth of how many times a callback was wrapped in another callback.

For one iteration, while is the same as if so that doesn't really matter. However, if someone called lookup_str with callback which was itself a callback, while would still just keep on to work.