def get_span(self, request=None):
if request is None and stack.top:<EOL><INDENT>request = stack.top.request<EOL><DEDENT>scope = self._current_scopes.get(request, None)<EOL>return None if scope is None else scope.span<EOL>
Returns the span tracing `request`, or the current request if
`request==None`.

If there is no such span, get_span returns None.

@param request the request to get the span from