Create a child span for the current span and append it to the child
        spans list.

        :type name: str
        :param name: (Optional) The name of the child span.

        :rtype: :class: `~opencensus.trace.blankspan.BlankSpan`
        :returns: A child Span to be added to the current span.

def span(self, name='child_span'):
        """Create a child span for the current span and append it to the child
        spans list.

        :type name: str
        :param name: (Optional) The name of the child span.

        :rtype: :class: `~opencensus.trace.blankspan.BlankSpan`
        :returns: A child Span to be added to the current span.
        """
        child_span = BlankSpan(name, parent_span=self)
        self._child_spans.append(child_span)
        return child_span