[Core][OTel] Update settings to include opentelemetry (Azure#29095)

Signed-off-by: Paul Van Eck <paulvaneck@microsoft.com>

Author: pvaneck

sdk/core/azure-core-tracing-opentelemetry/README.md

@@ -25,6 +25,12 @@ with azure-core tracing. This includes (not exhaustive list), azure-storage-blob
     from azure.core.tracing.ext.opentelemetry_span import OpenTelemetrySpan
     settings.tracing_implementation = OpenTelemetrySpan
   ```
+* Alternatively, if you have the latest version of `azure-core` installed, you can also set the following environment variable to
+  enable tracing with OpenTelemetry:
+
+  ```bash
+  AZURE_SDK_TRACING_IMPLEMENTATION=opentelemetry
+  ```
 
 ## Examples
 

sdk/core/azure-core/azure/core/settings.py

@@ -31,17 +31,9 @@
 import logging
 import os
 import sys
-from typing import Type, Optional, Callable, cast, Union, Dict, TYPE_CHECKING
+from typing import Type, Optional, Callable, cast, Union, Dict
 from azure.core.tracing import AbstractSpan
 
-if TYPE_CHECKING:
-    try:
-        # pylint:disable=unused-import
-        from azure.core.tracing.ext.opencensus_span import (
-            OpenCensusSpan,
-        )  # pylint:disable=redefined-outer-name
-    except ImportError:
-        pass
 
 __all__ = ("settings", "Settings")
 
@@ -115,8 +107,8 @@ def convert_logging(value: Union[str, int]) -> int:
     return level
 
 
-def get_opencensus_span() -> Optional[Type[AbstractSpan]]:
-    """Returns the OpenCensusSpan if opencensus is installed else returns None"""
+def _get_opencensus_span() -> Optional[Type[AbstractSpan]]:
+    """Returns the OpenCensusSpan if the opencensus tracing plugin is installed else returns None"""
     try:
         from azure.core.tracing.ext.opencensus_span import (  # pylint:disable=redefined-outer-name
             OpenCensusSpan,
@@ -127,14 +119,33 @@ def get_opencensus_span() -> Optional[Type[AbstractSpan]]:
         return None
 
 
-def get_opencensus_span_if_opencensus_is_imported() -> Optional[Type[AbstractSpan]]:
+def _get_opentelemetry_span() -> Optional[Type[AbstractSpan]]:
+    """Returns the OpenTelemetrySpan if the opentelemetry tracing plugin is installed else returns None"""
+    try:
+        from azure.core.tracing.ext.opentelemetry_span import (  # pylint:disable=redefined-outer-name
+            OpenTelemetrySpan,
+        )
+
+        return OpenTelemetrySpan
+    except ImportError:
+        return None
+
+
+def _get_opencensus_span_if_opencensus_is_imported() -> Optional[Type[AbstractSpan]]:
     if "opencensus" not in sys.modules:
         return None
-    return get_opencensus_span()
+    return _get_opencensus_span()
+
+
+def _get_opentelemetry_span_if_opentelemetry_is_imported() -> Optional[Type[AbstractSpan]]:
+    if "opentelemetry" not in sys.modules:
+        return None
+    return _get_opentelemetry_span()
 
 
 _tracing_implementation_dict: Dict[str, Callable[[], Optional[Type[AbstractSpan]]]] = {
-    "opencensus": get_opencensus_span
+    "opencensus": _get_opencensus_span,
+    "opentelemetry": _get_opentelemetry_span,
 }
 
 
@@ -145,6 +156,7 @@ def convert_tracing_impl(value: Union[str, Type[AbstractSpan]]) -> Optional[Type
     understands the following strings, ignoring case:
 
     * "opencensus"
+    * "opentelemetry"
 
     :param value: the value to convert
     :type value: string
@@ -153,7 +165,9 @@ def convert_tracing_impl(value: Union[str, Type[AbstractSpan]]) -> Optional[Type
 
     """
     if value is None:
-        return get_opencensus_span_if_opencensus_is_imported()
+        return (
+            _get_opentelemetry_span_if_opentelemetry_is_imported() or _get_opencensus_span_if_opencensus_is_imported()
+        )
 
     if not isinstance(value, str):
         value = cast(Type[AbstractSpan], value)