api: Add several configuration related fixes (#583)

Fixes #582

This makes the attributes of the configuration object case sensitive in order to match better the environment variables that are too.

This makes the attributes of the configuration object accept any legal Python variable name (Configuration().some_2_attribute) is valid now.

This makes non-defined attributes return None when queried instead of raising an AttributeError. This makes it easier to use the configuration object because the user won't have to check for the existence of the attribute beforehand:

if Configuration().some_attribute == "value":
    # do stuff

instead of

if hasattr(Configuration(), "some_attribute") and Configuration().some_attribute == "value":
    # do stuff

opentelemetry-api/src/opentelemetry/configuration/__init__.py

@@ -19,27 +19,27 @@
 Simple configuration manager
 
 This is a configuration manager for OpenTelemetry. It reads configuration
-values from environment variables prefixed with
-``OPENTELEMETRY_PYTHON_`` whose characters are only all caps and underscores.
-The first character after ``OPENTELEMETRY_PYTHON_`` must be an uppercase
-character.
+values from environment variables prefixed with ``OPENTELEMETRY_PYTHON_`` whose
+characters are only alphanumeric characters and unserscores, except for the
+first character after ``OPENTELEMETRY_PYTHON_`` which must not be a number.
 
 For example, these environment variables will be read:
 
 1. ``OPENTELEMETRY_PYTHON_SOMETHING``
 2. ``OPENTELEMETRY_PYTHON_SOMETHING_ELSE_``
 3. ``OPENTELEMETRY_PYTHON_SOMETHING_ELSE_AND__ELSE``
+4. ``OPENTELEMETRY_PYTHON_SOMETHING_ELSE_AND_else``
+4. ``OPENTELEMETRY_PYTHON_SOMETHING_ELSE_AND_else2``
 
 These won't:
 
 1. ``OPENTELEMETRY_PYTH_SOMETHING``
-2. ``OPENTELEMETRY_PYTHON_something``
-3. ``OPENTELEMETRY_PYTHON_SOMETHING_2_AND__ELSE``
-4. ``OPENTELEMETRY_PYTHON_SOMETHING_%_ELSE``
+2. ``OPENTELEMETRY_PYTHON_2_SOMETHING_AND__ELSE``
+3. ``OPENTELEMETRY_PYTHON_SOMETHING_%_ELSE``
 
 The values stored in the environment variables can be found in an instance of
 ``opentelemetry.configuration.Configuration``. This class can be instantiated
-freely because instantiating it returns a singleton.
+freely because instantiating it returns always the same object.
 
 For example, if the environment variable
 ``OPENTELEMETRY_PYTHON_METER_PROVIDER`` value is ``my_meter_provider``, then
@@ -93,11 +93,13 @@ def __new__(cls) -> "Configuration":
 
             for key, value in environ.items():
 
-                match = fullmatch("OPENTELEMETRY_PYTHON_([A-Z][A-Z_]*)", key)
+                match = fullmatch(
+                    r"OPENTELEMETRY_PYTHON_([A-Za-z_][\w_]*)", key
+                )
 
                 if match is not None:
 
-                    key = match.group(1).lower()
+                    key = match.group(1)
 
                     setattr(Configuration, "_{}".format(key), value)
                     setattr(

opentelemetry-api/tests/configuration/test_configuration.py

@@ -21,6 +21,9 @@
 
 class TestConfiguration(TestCase):
     def setUp(self):
+        # This is added here to force a reload of the whole Configuration
+        # class, resetting its internal attributes so that each tests starts
+        # with a clean class.
         from opentelemetry.configuration import Configuration  # type: ignore
 
     def tearDown(self):
@@ -35,27 +38,37 @@ def test_singleton(self):
         {
             "OPENTELEMETRY_PYTHON_METER_PROVIDER": "meter_provider",
             "OPENTELEMETRY_PYTHON_TRACER_PROVIDER": "tracer_provider",
+            "OPENTELEMETRY_PYTHON_OThER": "other",
+            "OPENTELEMETRY_PYTHON_OTHER_7": "other_7",
+            "OPENTELEMETRY_PTHON_TRACEX_PROVIDER": "tracex_provider",
         },
     )
     def test_environment_variables(self):  # type: ignore
         self.assertEqual(
-            Configuration().meter_provider, "meter_provider"
+            Configuration().METER_PROVIDER, "meter_provider"
         )  # pylint: disable=no-member
         self.assertEqual(
-            Configuration().tracer_provider, "tracer_provider"
+            Configuration().TRACER_PROVIDER, "tracer_provider"
         )  # pylint: disable=no-member
+        self.assertEqual(
+            Configuration().OThER, "other"
+        )  # pylint: disable=no-member
+        self.assertEqual(
+            Configuration().OTHER_7, "other_7"
+        )  # pylint: disable=no-member
+        self.assertIsNone(Configuration().TRACEX_PROVIDER)
 
     @patch.dict(
         "os.environ",  # type: ignore
         {"OPENTELEMETRY_PYTHON_TRACER_PROVIDER": "tracer_provider"},
     )
     def test_property(self):
         with self.assertRaises(AttributeError):
-            Configuration().tracer_provider = "new_tracer_provider"
+            Configuration().TRACER_PROVIDER = "new_tracer_provider"
 
     def test_slots(self):
         with self.assertRaises(AttributeError):
-            Configuration().xyz = "xyz"  # pylint: disable=assigning-non-slot
+            Configuration().XYZ = "xyz"  # pylint: disable=assigning-non-slot
 
     def test_getattr(self):
-        Configuration().xyz is None
+        self.assertIsNone(Configuration().XYZ)