urlresolvers.py 文件源码

def get_callable(lookup_view, can_fail=False):
    """
    Return a callable corresponding to lookup_view. This function is used
    by both resolve() and reverse(), so can_fail allows the caller to choose
    between returning the input as is and raising an exception when the input
    string can't be interpreted as an import path.

    If lookup_view is already a callable, return it.
    If lookup_view is a string import path that can be resolved to a callable,
      import that callable and return it.
    If lookup_view is some other kind of string and can_fail is True, the string
      is returned as is. If can_fail is False, an exception is raised (either
      ImportError or ViewDoesNotExist).
    """
    if callable(lookup_view):
        return lookup_view

    mod_name, func_name = get_mod_func(lookup_view)
    if not func_name:  # No '.' in lookup_view
        if can_fail:
            return lookup_view
        else:
            raise ImportError(
                "Could not import '%s'. The path must be fully qualified." %
                lookup_view)

    try:
        mod = import_module(mod_name)
    except ImportError:
        if can_fail:
            return lookup_view
        else:
            parentmod, submod = get_mod_func(mod_name)
            if submod and not module_has_submodule(import_module(parentmod), submod):
                raise ViewDoesNotExist(
                    "Could not import '%s'. Parent module %s does not exist." %
                    (lookup_view, mod_name))
            else:
                raise
    else:
        try:
            view_func = getattr(mod, func_name)
        except AttributeError:
            if can_fail:
                return lookup_view
            else:
                raise ViewDoesNotExist(
                    "Could not import '%s'. View does not exist in module %s." %
                    (lookup_view, mod_name))
        else:
            if not callable(view_func):
                # For backwards compatibility this is raised regardless of can_fail
                raise ViewDoesNotExist(
                    "Could not import '%s.%s'. View is not callable." %
                    (mod_name, func_name))

            return view_func