sdk: Span.resource will now default to an empty resource (#724)

Right now, A resource object attached to a Span can be None. That means that there's two similar objects that refer to an empty resource: None, and the _EMPTY_RESOURCE global.

We should just always default to the _EMPTY_RESOURCE object: this avoids None checks in exporters.

Co-authored-by: Yusuke Tsutsumi <[email protected]>

Author: yashmehrotra

docs/sdk/resources.rst

@@ -0,0 +1,7 @@
+opentelemetry.sdk.resources package
+==========================================
+
+.. automodule:: opentelemetry.sdk.resources
+    :members:
+    :undoc-members:
+    :show-inheritance:

docs/sdk/sdk.rst

@@ -7,4 +7,5 @@ OpenTelemetry Python SDK
     :maxdepth: 1
 
     metrics
-    trace
+    resources
+    trace

ext/opentelemetry-ext-jaeger/src/opentelemetry/ext/jaeger/__init__.py

@@ -197,8 +197,7 @@ def _translate_to_jaeger(spans: Span):
         parent_id = span.parent.span_id if span.parent else 0
 
         tags = _extract_tags(span.attributes)
-        if span.resource:
-            tags.extend(_extract_tags(span.resource.labels))
+        tags.extend(_extract_tags(span.resource.labels))
 
         tags.extend(
             [

opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py

@@ -264,7 +264,7 @@ def __init__(
         parent: Optional[trace_api.SpanContext] = None,
         sampler: Optional[sampling.Sampler] = None,
         trace_config: None = None,  # TODO
-        resource: None = None,
+        resource: Resource = Resource.create_empty(),
         attributes: types.Attributes = None,  # TODO
         events: Sequence[Event] = None,  # TODO
         links: Sequence[trace_api.Link] = (),