runtime.py 文件源码

def get_namespace(self, uri):
        """Return a :class:`.Namespace` corresponding to the given ``uri``.

        If the given ``uri`` is a relative URI (i.e. it does not
        contain a leading slash ``/``), the ``uri`` is adjusted to
        be relative to the ``uri`` of the namespace itself. This
        method is therefore mostly useful off of the built-in
        ``local`` namespace, described in :ref:`namespace_local`.

        In
        most cases, a template wouldn't need this function, and
        should instead use the ``<%namespace>`` tag to load
        namespaces. However, since all ``<%namespace>`` tags are
        evaluated before the body of a template ever runs,
        this method can be used to locate namespaces using
        expressions that were generated within the body code of
        the template, or to conditionally use a particular
        namespace.

        """
        key = (self, uri)
        if key in self.context.namespaces:
            return self.context.namespaces[key]
        else:
            ns = TemplateNamespace(uri, self.context._copy(),
                                   templateuri=uri,
                                   calling_uri=self._templateuri)
            self.context.namespaces[key] = ns
            return ns