def get_spec_from_request(self, prefix):
        """Re-extract spec from request.path.
        Get the original, raw spec, without tornado's unquoting.
        This is needed because tornado converts 'foo%2Fbar/ref' to 'foo/bar/ref'.
        """
        idx = self.request.path.index(prefix)
        spec = self.request.path[idx + len(prefix) + 1 :]
        return spec
Re-extract spec from request.path.
        Get the original, raw spec, without tornado's unquoting.
        This is needed because tornado converts 'foo%2Fbar/ref' to 'foo/bar/ref'.
        
binderhub/base.py