Start a span.

        :type name: str
        :param name: The name of the span.

        :rtype: :class:`~opencensus.trace.trace_span.Span`
        :returns: The Span object.

def start_span(self, name='span'):
        """Start a span.

        :type name: str
        :param name: The name of the span.

        :rtype: :class:`~opencensus.trace.trace_span.Span`
        :returns: The Span object.
        """
        span = trace_span.BlankSpan(name, context_tracer=self)
        return span