How to use the opentelemetry-api.src.opentelemetry.trace.__init__.Span function in opentelemetry-api

def is_valid(self) -> bool:
        """Get whether this `SpanContext` is valid.

        A `SpanContext` is said to be invalid if its trace ID or span ID is
        invalid (i.e. ``0``).

        Returns:
            True if the `SpanContext` is valid, false otherwise.
        """
        return (
            self.trace_id != INVALID_TRACE_ID
            and self.span_id != INVALID_SPAN_ID
        )


class DefaultSpan(Span):
    """The default Span that is used when no Span implementation is available.

    All operations are no-op except context propagation.
    """

    def __init__(self, context: "SpanContext") -> None:
        self._context = context

    def get_context(self) -> "SpanContext":
        return self._context

    def is_recording_events(self) -> bool:
        return False


INVALID_SPAN_ID = 0x0000000000000000

instrumenting library.  Usually this should be the same as
                ``pkg_resources.get_distribution(instrumenting_library_name).version``.
        """
        return Tracer()


class Tracer:
    """Handles span creation and in-process context propagation.

    This class provides methods for manipulating the context, creating spans,
    and controlling spans' lifecycles.
    """

    # Constant used to represent the current span being used as a parent.
    # This is the default behavior when creating spans.
    CURRENT_SPAN = Span()

    def get_current_span(self) -> "Span":
        """Gets the currently active span from the context.

        If there is no current span, return a placeholder span with an invalid
        context.

        Returns:
            The currently active :class:`.Span`, or a placeholder span with an
            invalid :class:`.SpanContext`.
        """
        # pylint: disable=no-self-use
        return INVALID_SPAN

    def start_span(
        self,