allow user to enable env AZURE_PURE_CORE to opt in "small core"

sdk/core/azure-core/azure/core/__init__.py

@@ -24,20 +24,22 @@
 #
 # --------------------------------------------------------------------------
 
+import os
 from ._version import VERSION
 __version__ = VERSION
 
-from ._pipeline_client import PipelineClient
-from ._match_conditions import MatchConditions
+if not os.environ.get('AZURE_PURE_CORE', None) == 'True':
+    from .pipeline_client import PipelineClient
+    from .match_conditions import MatchConditions
 
 
-__all__ = [
-    "PipelineClient",
-    "MatchConditions"
-]
+    __all__ = [
+        "PipelineClient",
+        "MatchConditions"
+    ]
 
-try:
-    from ._pipeline_client_async import AsyncPipelineClient #pylint: disable=unused-import
-    __all__.extend(["AsyncPipelineClient"])
-except (ImportError, SyntaxError): # Python <= 3.5
-    pass
+    try:
+        from .pipeline_client_async import AsyncPipelineClient #pylint: disable=unused-import
+        __all__.extend(["AsyncPipelineClient"])
+    except (ImportError, SyntaxError): # Python <= 3.5
+        pass