From 989c3e750c6d57c579e1a9f2244a95a0286abc3e Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Fri, 5 Jul 2019 11:26:01 -0700
Subject: [PATCH 01/20] steal context lib from OpenCensus

---
 .../src/opentelemetry/context/__init__.py     | 132 ++++++++++++++++++
 1 file changed, 132 insertions(+)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index d853a7bcf65..e02402e33f4 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -11,3 +11,135 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+
+
+try:
+    import contextvars
+except ImportError:
+    contextvars = None
+
+import threading
+
+__all__ = ['RuntimeContext']
+
+
+class _RuntimeContext(object):
+    _lock = threading.Lock()
+    _slots = {}
+
+    @classmethod
+    def clear(cls):
+        """Clear all slots to their default value."""
+        for name in cls._slots.keys():
+            slot = cls._slots[name]
+            slot.clear()
+
+    @classmethod
+    def register_slot(cls, name, default=None):
+        """Register a context slot with an optional default value.
+
+        :type name: str
+        :param name: The name of the context slot.
+
+        :type default: object
+        :param name: The default value of the slot, can be a value or lambda.
+
+        :returns: The registered slot.
+        """
+        with cls._lock:
+            if name in cls._slots:
+                raise ValueError('slot {} already registered'.format(name))
+            slot = cls.Slot(name, default)
+            cls._slots[name] = slot
+            return slot
+
+    def apply(self, snapshot):
+        """Set the current context from a given snapshot dictionary"""
+
+        for name in snapshot:
+            setattr(self, name, snapshot[name])
+
+    def snapshot(self):
+        """Return a dictionary of current slots by reference."""
+
+        return dict((n, self._slots[n].get()) for n in self._slots.keys())
+
+    def __repr__(self):
+        return ('{}({})'.format(type(self).__name__, self.snapshot()))
+
+    def __getattr__(self, name):
+        if name not in self._slots:
+            self.register_slot(name, None)
+        slot = self._slots[name]
+        return slot.get()
+
+    def __setattr__(self, name, value):
+        if name not in self._slots:
+            self.register_slot(name, None)
+        slot = self._slots[name]
+        slot.set(value)
+
+    def with_current_context(self, func):
+        """Capture the current context and apply it to the provided func"""
+
+        caller_context = self.snapshot()
+
+        def call_with_current_context(*args, **kwargs):
+            try:
+                backup_context = self.snapshot()
+                self.apply(caller_context)
+                return func(*args, **kwargs)
+            finally:
+                self.apply(backup_context)
+
+        return call_with_current_context
+
+
+class _ThreadLocalRuntimeContext(_RuntimeContext):
+    class Slot(object):
+        _thread_local = threading.local()
+
+        def __init__(self, name, default):
+            self.name = name
+            self.default = default if callable(default) else (lambda: default)
+
+        def clear(self):
+            setattr(self._thread_local, self.name, self.default())
+
+        def get(self):
+            try:
+                return getattr(self._thread_local, self.name)
+            except AttributeError:
+                value = self.default()
+                self.set(value)
+                return value
+
+        def set(self, value):
+            setattr(self._thread_local, self.name, value)
+
+
+class _AsyncRuntimeContext(_RuntimeContext):
+    class Slot(object):
+        def __init__(self, name, default):
+            self.name = name
+            self.contextvar = contextvars.ContextVar(name)
+            self.default = default if callable(default) else (lambda: default)
+
+        def clear(self):
+            self.contextvar.set(self.default())
+
+        def get(self):
+            try:
+                return self.contextvar.get()
+            except LookupError:
+                value = self.default()
+                self.set(value)
+                return value
+
+        def set(self, value):
+            self.contextvar.set(value)
+
+
+RuntimeContext = _ThreadLocalRuntimeContext()
+if contextvars:
+    RuntimeContext = _AsyncRuntimeContext()

From dd979b2790414e27b83b219e314b36659e4afb2e Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 14:20:31 -0700
Subject: [PATCH 02/20] lint

---
 .../src/opentelemetry/context/__init__.py              | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index e02402e33f4..48a85faf0d3 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -23,7 +23,7 @@
 __all__ = ['RuntimeContext']
 
 
-class _RuntimeContext(object):
+class _RuntimeContext:
     _lock = threading.Lock()
     _slots = {}
 
@@ -65,7 +65,7 @@ def snapshot(self):
         return dict((n, self._slots[n].get()) for n in self._slots.keys())
 
     def __repr__(self):
-        return ('{}({})'.format(type(self).__name__, self.snapshot()))
+        return '{}({})'.format(type(self).__name__, self.snapshot())
 
     def __getattr__(self, name):
         if name not in self._slots:
@@ -96,7 +96,7 @@ def call_with_current_context(*args, **kwargs):
 
 
 class _ThreadLocalRuntimeContext(_RuntimeContext):
-    class Slot(object):
+    class Slot:
         _thread_local = threading.local()
 
         def __init__(self, name, default):
@@ -140,6 +140,6 @@ def set(self, value):
             self.contextvar.set(value)
 
 
-RuntimeContext = _ThreadLocalRuntimeContext()
+RuntimeContext = _ThreadLocalRuntimeContext()  # pylint:disable=C0201
 if contextvars:
-    RuntimeContext = _AsyncRuntimeContext()
+    RuntimeContext = _AsyncRuntimeContext()  # pylint:disable=C0201

From e6fbe91d8ce5bcc3531db78d1885429489493941 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 21:21:47 -0700
Subject: [PATCH 03/20] lint

---
 .../src/opentelemetry/context/__init__.py              | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index 48a85faf0d3..f558e7e0e38 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -30,7 +30,7 @@ class _RuntimeContext:
     @classmethod
     def clear(cls):
         """Clear all slots to their default value."""
-        for name in cls._slots.keys():
+        for name in cls._slots.keys():  # pylint:disable=consider-iterating-dictionary
             slot = cls._slots[name]
             slot.clear()
 
@@ -62,7 +62,7 @@ def apply(self, snapshot):
     def snapshot(self):
         """Return a dictionary of current slots by reference."""
 
-        return dict((n, self._slots[n].get()) for n in self._slots.keys())
+        return dict((n, self._slots[n].get()) for n in self._slots.keys())  # pylint:disable=consider-iterating-dictionary
 
     def __repr__(self):
         return '{}({})'.format(type(self).__name__, self.snapshot())
@@ -119,7 +119,7 @@ def set(self, value):
 
 
 class _AsyncRuntimeContext(_RuntimeContext):
-    class Slot(object):
+    class Slot:
         def __init__(self, name, default):
             self.name = name
             self.contextvar = contextvars.ContextVar(name)
@@ -140,6 +140,6 @@ def set(self, value):
             self.contextvar.set(value)
 
 
-RuntimeContext = _ThreadLocalRuntimeContext()  # pylint:disable=C0201
+RuntimeContext = _ThreadLocalRuntimeContext()  # pylint:disable=invalid-name
 if contextvars:
-    RuntimeContext = _AsyncRuntimeContext()  # pylint:disable=C0201
+    RuntimeContext = _AsyncRuntimeContext()  # pylint:disable=invalid-name

From 44e5897ed4555a446fd7716b4703f67773a34652 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 21:25:45 -0700
Subject: [PATCH 04/20] lint

---
 opentelemetry-api/src/opentelemetry/context/__init__.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index f558e7e0e38..56df9a10bb3 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -30,7 +30,8 @@ class _RuntimeContext:
     @classmethod
     def clear(cls):
         """Clear all slots to their default value."""
-        for name in cls._slots.keys():  # pylint:disable=consider-iterating-dictionary
+        keys = cls._slots.keys()
+        for name in keys:
             slot = cls._slots[name]
             slot.clear()
 
@@ -62,7 +63,8 @@ def apply(self, snapshot):
     def snapshot(self):
         """Return a dictionary of current slots by reference."""
 
-        return dict((n, self._slots[n].get()) for n in self._slots.keys())  # pylint:disable=consider-iterating-dictionary
+        keys = self._slots.keys()
+        return dict((n, self._slots[n].get()) for n in keys)
 
     def __repr__(self):
         return '{}({})'.format(type(self).__name__, self.snapshot())

From beaa000c9ba89e72d7a7e559760769cf94de0754 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 21:35:33 -0700
Subject: [PATCH 05/20] type hint

---
 opentelemetry-api/src/opentelemetry/context/__init__.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index 56df9a10bb3..f22d19e9f75 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -19,13 +19,14 @@
     contextvars = None
 
 import threading
+import typing
 
 __all__ = ['RuntimeContext']
 
 
 class _RuntimeContext:
     _lock = threading.Lock()
-    _slots = {}
+    _slots : typing.Dict[str, typing.Any] = {}
 
     @classmethod
     def clear(cls):

From 9f71780f47609e35cd1234d5a83d03cef1a43fcb Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 21:42:39 -0700
Subject: [PATCH 06/20] type hint

---
 .../src/opentelemetry/context/__init__.py      | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index f22d19e9f75..6d2f92bee39 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -26,7 +26,7 @@
 
 class _RuntimeContext:
     _lock = threading.Lock()
-    _slots : typing.Dict[str, typing.Any] = {}
+    _slots : typing.Dict[str, Slot] = {}
 
     @classmethod
     def clear(cls):
@@ -55,6 +55,18 @@ def register_slot(cls, name, default=None):
             cls._slots[name] = slot
             return slot
 
+
+    class Slot:
+        def clear(self):
+            raise NotImplementedError
+
+        def get(self):
+            raise NotImplementedError
+
+        def set(self, value):
+            raise NotImplementedError
+
+
     def apply(self, snapshot):
         """Set the current context from a given snapshot dictionary"""
 
@@ -99,7 +111,7 @@ def call_with_current_context(*args, **kwargs):
 
 
 class _ThreadLocalRuntimeContext(_RuntimeContext):
-    class Slot:
+    class Slot(_RuntimeContext.Slot):
         _thread_local = threading.local()
 
         def __init__(self, name, default):
@@ -122,7 +134,7 @@ def set(self, value):
 
 
 class _AsyncRuntimeContext(_RuntimeContext):
-    class Slot:
+    class Slot(_RuntimeContext.Slot):
         def __init__(self, name, default):
             self.name = name
             self.contextvar = contextvars.ContextVar(name)

From 90fde070c3996c501a5c9b0c8592be402f0cce95 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 21:45:04 -0700
Subject: [PATCH 07/20] type hint

---
 .../src/opentelemetry/context/__init__.py     | 24 +++++++++----------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index 6d2f92bee39..12d8ca2ad03 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -25,8 +25,18 @@
 
 
 class _RuntimeContext:
+    class Slot:
+        def clear(self):
+            raise NotImplementedError
+
+        def get(self):
+            raise NotImplementedError
+
+        def set(self, value):
+            raise NotImplementedError
+
     _lock = threading.Lock()
-    _slots : typing.Dict[str, Slot] = {}
+    _slots: typing.Dict[str, Slot] = {}
 
     @classmethod
     def clear(cls):
@@ -55,18 +65,6 @@ def register_slot(cls, name, default=None):
             cls._slots[name] = slot
             return slot
 
-
-    class Slot:
-        def clear(self):
-            raise NotImplementedError
-
-        def get(self):
-            raise NotImplementedError
-
-        def set(self, value):
-            raise NotImplementedError
-
-
     def apply(self, snapshot):
         """Set the current context from a given snapshot dictionary"""
 

From b8ca3e487848f7eaa7f7d12cc5efadaaedc67375 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 22:05:09 -0700
Subject: [PATCH 08/20] type hint

---
 opentelemetry-api/src/opentelemetry/context/__init__.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index 12d8ca2ad03..41d88ff4356 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -12,14 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import threading
+import types
+import typing
 
 try:
     import contextvars
 except ImportError:
-    contextvars = None
-
-import threading
-import typing
+    contextvars: types.ModuleType = None
 
 __all__ = ['RuntimeContext']
 

From 00a256c0b2f3b57e17d3d4a6f5803424fdb99903 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 22:57:20 -0700
Subject: [PATCH 09/20] refactor

---
 .../src/opentelemetry/context/__init__.py     | 148 +-----------------
 .../opentelemetry/context/async_context.py    |  38 +++++
 .../src/opentelemetry/context/base_context.py |  99 ++++++++++++
 .../context/thread_local_context.py           |  40 +++++
 4 files changed, 185 insertions(+), 140 deletions(-)
 create mode 100644 opentelemetry-api/src/opentelemetry/context/async_context.py
 create mode 100644 opentelemetry-api/src/opentelemetry/context/base_context.py
 create mode 100644 opentelemetry-api/src/opentelemetry/context/thread_local_context.py

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index 41d88ff4356..c8e4087af38 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -12,147 +12,15 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import threading
-import types
-import typing
-
-try:
-    import contextvars
-except ImportError:
-    contextvars: types.ModuleType = None
+from .base_context import BaseRuntimeContext
 
 __all__ = ['RuntimeContext']
 
+RuntimeContext: BaseRuntimeContext = None
 
-class _RuntimeContext:
-    class Slot:
-        def clear(self):
-            raise NotImplementedError
-
-        def get(self):
-            raise NotImplementedError
-
-        def set(self, value):
-            raise NotImplementedError
-
-    _lock = threading.Lock()
-    _slots: typing.Dict[str, Slot] = {}
-
-    @classmethod
-    def clear(cls):
-        """Clear all slots to their default value."""
-        keys = cls._slots.keys()
-        for name in keys:
-            slot = cls._slots[name]
-            slot.clear()
-
-    @classmethod
-    def register_slot(cls, name, default=None):
-        """Register a context slot with an optional default value.
-
-        :type name: str
-        :param name: The name of the context slot.
-
-        :type default: object
-        :param name: The default value of the slot, can be a value or lambda.
-
-        :returns: The registered slot.
-        """
-        with cls._lock:
-            if name in cls._slots:
-                raise ValueError('slot {} already registered'.format(name))
-            slot = cls.Slot(name, default)
-            cls._slots[name] = slot
-            return slot
-
-    def apply(self, snapshot):
-        """Set the current context from a given snapshot dictionary"""
-
-        for name in snapshot:
-            setattr(self, name, snapshot[name])
-
-    def snapshot(self):
-        """Return a dictionary of current slots by reference."""
-
-        keys = self._slots.keys()
-        return dict((n, self._slots[n].get()) for n in keys)
-
-    def __repr__(self):
-        return '{}({})'.format(type(self).__name__, self.snapshot())
-
-    def __getattr__(self, name):
-        if name not in self._slots:
-            self.register_slot(name, None)
-        slot = self._slots[name]
-        return slot.get()
-
-    def __setattr__(self, name, value):
-        if name not in self._slots:
-            self.register_slot(name, None)
-        slot = self._slots[name]
-        slot.set(value)
-
-    def with_current_context(self, func):
-        """Capture the current context and apply it to the provided func"""
-
-        caller_context = self.snapshot()
-
-        def call_with_current_context(*args, **kwargs):
-            try:
-                backup_context = self.snapshot()
-                self.apply(caller_context)
-                return func(*args, **kwargs)
-            finally:
-                self.apply(backup_context)
-
-        return call_with_current_context
-
-
-class _ThreadLocalRuntimeContext(_RuntimeContext):
-    class Slot(_RuntimeContext.Slot):
-        _thread_local = threading.local()
-
-        def __init__(self, name, default):
-            self.name = name
-            self.default = default if callable(default) else (lambda: default)
-
-        def clear(self):
-            setattr(self._thread_local, self.name, self.default())
-
-        def get(self):
-            try:
-                return getattr(self._thread_local, self.name)
-            except AttributeError:
-                value = self.default()
-                self.set(value)
-                return value
-
-        def set(self, value):
-            setattr(self._thread_local, self.name, value)
-
-
-class _AsyncRuntimeContext(_RuntimeContext):
-    class Slot(_RuntimeContext.Slot):
-        def __init__(self, name, default):
-            self.name = name
-            self.contextvar = contextvars.ContextVar(name)
-            self.default = default if callable(default) else (lambda: default)
-
-        def clear(self):
-            self.contextvar.set(self.default())
-
-        def get(self):
-            try:
-                return self.contextvar.get()
-            except LookupError:
-                value = self.default()
-                self.set(value)
-                return value
-
-        def set(self, value):
-            self.contextvar.set(value)
-
-
-RuntimeContext = _ThreadLocalRuntimeContext()  # pylint:disable=invalid-name
-if contextvars:
-    RuntimeContext = _AsyncRuntimeContext()  # pylint:disable=invalid-name
+try:
+    from .async_context import AsyncRuntimeContext
+    RuntimeContext = AsyncRuntimeContext()
+except ImportError:
+    from .thread_local_context import ThreadLocalRuntimeContext
+    RuntimeContext = ThreadLocalRuntimeContext()
diff --git a/opentelemetry-api/src/opentelemetry/context/async_context.py b/opentelemetry-api/src/opentelemetry/context/async_context.py
new file mode 100644
index 00000000000..b59fc33361e
--- /dev/null
+++ b/opentelemetry-api/src/opentelemetry/context/async_context.py
@@ -0,0 +1,38 @@
+# Copyright 2019, OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import contextvars
+
+from .base_context import BaseRuntimeContext
+
+class AsyncRuntimeContext(BaseRuntimeContext):
+    class Slot(BaseRuntimeContext.Slot):
+        def __init__(self, name, default):
+            self.name = name
+            self.contextvar = contextvars.ContextVar(name)
+            self.default = default if callable(default) else (lambda: default)
+
+        def clear(self):
+            self.contextvar.set(self.default())
+
+        def get(self):
+            try:
+                return self.contextvar.get()
+            except LookupError:
+                value = self.default()
+                self.set(value)
+                return value
+
+        def set(self, value):
+            self.contextvar.set(value)
diff --git a/opentelemetry-api/src/opentelemetry/context/base_context.py b/opentelemetry-api/src/opentelemetry/context/base_context.py
new file mode 100644
index 00000000000..0e0fbdc9a15
--- /dev/null
+++ b/opentelemetry-api/src/opentelemetry/context/base_context.py
@@ -0,0 +1,99 @@
+# Copyright 2019, OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import threading
+import typing
+
+class BaseRuntimeContext:
+    class Slot:
+        def clear(self):
+            raise NotImplementedError
+
+        def get(self):
+            raise NotImplementedError
+
+        def set(self, value):
+            raise NotImplementedError
+
+    _lock = threading.Lock()
+    _slots: typing.Dict[str, Slot] = {}
+
+    @classmethod
+    def clear(cls):
+        """Clear all slots to their default value."""
+        keys = cls._slots.keys()
+        for name in keys:
+            slot = cls._slots[name]
+            slot.clear()
+
+    @classmethod
+    def register_slot(cls, name, default=None):
+        """Register a context slot with an optional default value.
+
+        :type name: str
+        :param name: The name of the context slot.
+
+        :type default: object
+        :param name: The default value of the slot, can be a value or lambda.
+
+        :returns: The registered slot.
+        """
+        with cls._lock:
+            if name in cls._slots:
+                raise ValueError('slot {} already registered'.format(name))
+            slot = cls.Slot(name, default)
+            cls._slots[name] = slot
+            return slot
+
+    def apply(self, snapshot):
+        """Set the current context from a given snapshot dictionary"""
+
+        for name in snapshot:
+            setattr(self, name, snapshot[name])
+
+    def snapshot(self):
+        """Return a dictionary of current slots by reference."""
+
+        keys = self._slots.keys()
+        return dict((n, self._slots[n].get()) for n in keys)
+
+    def __repr__(self):
+        return '{}({})'.format(type(self).__name__, self.snapshot())
+
+    def __getattr__(self, name):
+        if name not in self._slots:
+            self.register_slot(name, None)
+        slot = self._slots[name]
+        return slot.get()
+
+    def __setattr__(self, name, value):
+        if name not in self._slots:
+            self.register_slot(name, None)
+        slot = self._slots[name]
+        slot.set(value)
+
+    def with_current_context(self, func):
+        """Capture the current context and apply it to the provided func"""
+
+        caller_context = self.snapshot()
+
+        def call_with_current_context(*args, **kwargs):
+            try:
+                backup_context = self.snapshot()
+                self.apply(caller_context)
+                return func(*args, **kwargs)
+            finally:
+                self.apply(backup_context)
+
+        return call_with_current_context
diff --git a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
new file mode 100644
index 00000000000..be1392557ca
--- /dev/null
+++ b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
@@ -0,0 +1,40 @@
+# Copyright 2019, OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import threading
+import typing
+
+from .base_context import BaseRuntimeContext
+
+class ThreadLocalRuntimeContext(BaseRuntimeContext):
+    class Slot(BaseRuntimeContext.Slot):
+        _thread_local = threading.local()
+
+        def __init__(self, name, default):
+            self.name = name
+            self.default = default if callable(default) else (lambda: default)
+
+        def clear(self):
+            setattr(self._thread_local, self.name, self.default())
+
+        def get(self):
+            try:
+                return getattr(self._thread_local, self.name)
+            except AttributeError:
+                value = self.default()
+                self.set(value)
+                return value
+
+        def set(self, value):
+            setattr(self._thread_local, self.name, value)

From 199054adbd35afa5c5a84efebd6107c3718b6db6 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 23:04:37 -0700
Subject: [PATCH 10/20] type hint

---
 .../src/opentelemetry/context/base_context.py | 24 +++++++++----------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/base_context.py b/opentelemetry-api/src/opentelemetry/context/base_context.py
index 0e0fbdc9a15..bb514a2d6d9 100644
--- a/opentelemetry-api/src/opentelemetry/context/base_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/base_context.py
@@ -17,20 +17,20 @@
 
 class BaseRuntimeContext:
     class Slot:
-        def clear(self):
+        def clear(self) -> None:
             raise NotImplementedError
 
-        def get(self):
+        def get(self) -> typing.Any:
             raise NotImplementedError
 
-        def set(self, value):
+        def set(self, value) -> None:
             raise NotImplementedError
 
     _lock = threading.Lock()
     _slots: typing.Dict[str, Slot] = {}
 
     @classmethod
-    def clear(cls):
+    def clear(cls) -> None:
         """Clear all slots to their default value."""
         keys = cls._slots.keys()
         for name in keys:
@@ -38,7 +38,7 @@ def clear(cls):
             slot.clear()
 
     @classmethod
-    def register_slot(cls, name, default=None):
+    def register_slot(cls, name: str, default: typing.Any = None) -> None:
         """Register a context slot with an optional default value.
 
         :type name: str
@@ -56,39 +56,39 @@ def register_slot(cls, name, default=None):
             cls._slots[name] = slot
             return slot
 
-    def apply(self, snapshot):
+    def apply(self, snapshot) -> None:
         """Set the current context from a given snapshot dictionary"""
 
         for name in snapshot:
             setattr(self, name, snapshot[name])
 
-    def snapshot(self):
+    def snapshot(self) -> typing.Dict[str, typing.Any]:
         """Return a dictionary of current slots by reference."""
 
         keys = self._slots.keys()
         return dict((n, self._slots[n].get()) for n in keys)
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return '{}({})'.format(type(self).__name__, self.snapshot())
 
-    def __getattr__(self, name):
+    def __getattr__(self, name) -> typing.Any:
         if name not in self._slots:
             self.register_slot(name, None)
         slot = self._slots[name]
         return slot.get()
 
-    def __setattr__(self, name, value):
+    def __setattr__(self, name, value) -> None:
         if name not in self._slots:
             self.register_slot(name, None)
         slot = self._slots[name]
         slot.set(value)
 
-    def with_current_context(self, func):
+    def with_current_context(self, func) -> typing.Callable:
         """Capture the current context and apply it to the provided func"""
 
         caller_context = self.snapshot()
 
-        def call_with_current_context(*args, **kwargs):
+        def call_with_current_context(*args, **kwargs) -> typing.Any:
             try:
                 backup_context = self.snapshot()
                 self.apply(caller_context)

From 023eac9cf1f9757a884f25149ac33e18469f747a Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 23:08:38 -0700
Subject: [PATCH 11/20] type hint

---
 opentelemetry-api/src/opentelemetry/context/__init__.py       | 4 ++--
 .../src/opentelemetry/context/thread_local_context.py         | 1 -
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index c8e4087af38..8220f629ecf 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -20,7 +20,7 @@
 
 try:
     from .async_context import AsyncRuntimeContext
-    RuntimeContext = AsyncRuntimeContext()
+    RuntimeContext = AsyncRuntimeContext() # pylint:disable=invalid-name
 except ImportError:
     from .thread_local_context import ThreadLocalRuntimeContext
-    RuntimeContext = ThreadLocalRuntimeContext()
+    RuntimeContext = ThreadLocalRuntimeContext() # pylint:disable=invalid-name
diff --git a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
index be1392557ca..fcded9f8a31 100644
--- a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
@@ -13,7 +13,6 @@
 # limitations under the License.
 
 import threading
-import typing
 
 from .base_context import BaseRuntimeContext
 

From f83cf89e4976cf55ef3796d36e494edfe1cf856e Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 23:13:54 -0700
Subject: [PATCH 12/20] type hint

---
 opentelemetry-api/src/opentelemetry/context/__init__.py   | 8 ++++----
 .../src/opentelemetry/context/async_context.py            | 1 +
 .../src/opentelemetry/context/base_context.py             | 1 +
 .../src/opentelemetry/context/thread_local_context.py     | 1 +
 4 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index 8220f629ecf..e9b8678fb06 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -14,13 +14,13 @@
 
 from .base_context import BaseRuntimeContext
 
-__all__ = ['RuntimeContext']
+__all__ = ['Context']
 
-RuntimeContext: BaseRuntimeContext = None
+Context: BaseRuntimeContext = None
 
 try:
     from .async_context import AsyncRuntimeContext
-    RuntimeContext = AsyncRuntimeContext() # pylint:disable=invalid-name
+    Context = AsyncRuntimeContext()  # pylint:disable=invalid-name
 except ImportError:
     from .thread_local_context import ThreadLocalRuntimeContext
-    RuntimeContext = ThreadLocalRuntimeContext() # pylint:disable=invalid-name
+    Context = ThreadLocalRuntimeContext()  # pylint:disable=invalid-name
diff --git a/opentelemetry-api/src/opentelemetry/context/async_context.py b/opentelemetry-api/src/opentelemetry/context/async_context.py
index b59fc33361e..5fd94dc0b37 100644
--- a/opentelemetry-api/src/opentelemetry/context/async_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/async_context.py
@@ -16,6 +16,7 @@
 
 from .base_context import BaseRuntimeContext
 
+
 class AsyncRuntimeContext(BaseRuntimeContext):
     class Slot(BaseRuntimeContext.Slot):
         def __init__(self, name, default):
diff --git a/opentelemetry-api/src/opentelemetry/context/base_context.py b/opentelemetry-api/src/opentelemetry/context/base_context.py
index bb514a2d6d9..769092a385d 100644
--- a/opentelemetry-api/src/opentelemetry/context/base_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/base_context.py
@@ -15,6 +15,7 @@
 import threading
 import typing
 
+
 class BaseRuntimeContext:
     class Slot:
         def clear(self) -> None:
diff --git a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
index fcded9f8a31..4fa0eeb733d 100644
--- a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
@@ -16,6 +16,7 @@
 
 from .base_context import BaseRuntimeContext
 
+
 class ThreadLocalRuntimeContext(BaseRuntimeContext):
     class Slot(BaseRuntimeContext.Slot):
         _thread_local = threading.local()

From 62517f0db1b8f62ea03eb13b4e9c80f79cdb7431 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 23:17:45 -0700
Subject: [PATCH 13/20] type hint

---
 mypy-relaxed.ini | 2 +-
 mypy.ini         | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mypy-relaxed.ini b/mypy-relaxed.ini
index 8f2be85affc..205688353e3 100644
--- a/mypy-relaxed.ini
+++ b/mypy-relaxed.ini
@@ -4,7 +4,7 @@
   disallow_any_unimported = True
 ; disallow_any_expr = True
   disallow_any_decorated = True
-  disallow_any_explicit = True
+; disallow_any_explicit = True
   disallow_any_generics = True
   disallow_subclassing_any = True
   disallow_untyped_calls = True
diff --git a/mypy.ini b/mypy.ini
index 5b46777838d..ba375b62b1d 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -2,7 +2,7 @@
   disallow_any_unimported = True
   disallow_any_expr = True
   disallow_any_decorated = True
-  disallow_any_explicit = True
+; disallow_any_explicit = True
   disallow_any_generics = True
   disallow_subclassing_any = True
   disallow_untyped_calls = True

From 937240e73f8bef01f2dfb87c9f0b6397d4089e48 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 23:22:18 -0700
Subject: [PATCH 14/20] type hint

---
 opentelemetry-api/src/opentelemetry/context/base_context.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/base_context.py b/opentelemetry-api/src/opentelemetry/context/base_context.py
index 769092a385d..3898fb57ba2 100644
--- a/opentelemetry-api/src/opentelemetry/context/base_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/base_context.py
@@ -18,13 +18,16 @@
 
 class BaseRuntimeContext:
     class Slot:
+        def __init__(self, name: str, default: typing.Any):
+            raise NotImplementedError
+
         def clear(self) -> None:
             raise NotImplementedError
 
         def get(self) -> typing.Any:
             raise NotImplementedError
 
-        def set(self, value) -> None:
+        def set(self, value: typing.Any) -> None:
             raise NotImplementedError
 
     _lock = threading.Lock()

From 2b2f553d78f50bc5dfa87124ff0a2c7a8609e209 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 23:26:20 -0700
Subject: [PATCH 15/20] type hint

---
 mypy-relaxed.ini                                            | 2 +-
 mypy.ini                                                    | 2 +-
 opentelemetry-api/src/opentelemetry/context/base_context.py | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/mypy-relaxed.ini b/mypy-relaxed.ini
index 205688353e3..9cd56789a1e 100644
--- a/mypy-relaxed.ini
+++ b/mypy-relaxed.ini
@@ -3,7 +3,7 @@
 [mypy]
   disallow_any_unimported = True
 ; disallow_any_expr = True
-  disallow_any_decorated = True
+; disallow_any_decorated = True
 ; disallow_any_explicit = True
   disallow_any_generics = True
   disallow_subclassing_any = True
diff --git a/mypy.ini b/mypy.ini
index ba375b62b1d..abb7aba2961 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,7 +1,7 @@
 [mypy]
   disallow_any_unimported = True
   disallow_any_expr = True
-  disallow_any_decorated = True
+; disallow_any_decorated = True
 ; disallow_any_explicit = True
   disallow_any_generics = True
   disallow_subclassing_any = True
diff --git a/opentelemetry-api/src/opentelemetry/context/base_context.py b/opentelemetry-api/src/opentelemetry/context/base_context.py
index 3898fb57ba2..67d42a10b49 100644
--- a/opentelemetry-api/src/opentelemetry/context/base_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/base_context.py
@@ -42,7 +42,7 @@ def clear(cls) -> None:
             slot.clear()
 
     @classmethod
-    def register_slot(cls, name: str, default: typing.Any = None) -> None:
+    def register_slot(cls, name: str, default: typing.Any = None) -> 'Slot':
         """Register a context slot with an optional default value.
 
         :type name: str
@@ -87,7 +87,7 @@ def __setattr__(self, name, value) -> None:
         slot = self._slots[name]
         slot.set(value)
 
-    def with_current_context(self, func) -> typing.Callable:
+    def with_current_context(self, func: typing.Callable) -> typing.Callable:
         """Capture the current context and apply it to the provided func"""
 
         caller_context = self.snapshot()

From 533fd2adb2924b08b204d2880fbb1645a05009f5 Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Wed, 17 Jul 2019 23:36:06 -0700
Subject: [PATCH 16/20] type hint

---
 opentelemetry-api/src/opentelemetry/context/async_context.py     | 1 +
 .../src/opentelemetry/context/thread_local_context.py            | 1 +
 2 files changed, 2 insertions(+)

diff --git a/opentelemetry-api/src/opentelemetry/context/async_context.py b/opentelemetry-api/src/opentelemetry/context/async_context.py
index 5fd94dc0b37..614cfaacc0d 100644
--- a/opentelemetry-api/src/opentelemetry/context/async_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/async_context.py
@@ -20,6 +20,7 @@
 class AsyncRuntimeContext(BaseRuntimeContext):
     class Slot(BaseRuntimeContext.Slot):
         def __init__(self, name, default):
+            # pylint: disable=super-init-not-called
             self.name = name
             self.contextvar = contextvars.ContextVar(name)
             self.default = default if callable(default) else (lambda: default)
diff --git a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
index 4fa0eeb733d..9830aa83b03 100644
--- a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
@@ -22,6 +22,7 @@ class Slot(BaseRuntimeContext.Slot):
         _thread_local = threading.local()
 
         def __init__(self, name, default):
+            # pylint: disable=super-init-not-called
             self.name = name
             self.default = default if callable(default) else (lambda: default)
 

From 123887e96babe0bb2e16d1272b0996342efa154e Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Thu, 18 Jul 2019 00:12:28 -0700
Subject: [PATCH 17/20] type hint

---
 .../src/opentelemetry/context/__init__.py     |  4 +++-
 .../opentelemetry/context/async_context.py    | 13 +++++++------
 .../src/opentelemetry/context/base_context.py | 19 +++++++++++++------
 .../context/thread_local_context.py           |  9 +++++----
 4 files changed, 28 insertions(+), 17 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index e9b8678fb06..c2fe840cb44 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -12,11 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import typing
+
 from .base_context import BaseRuntimeContext
 
 __all__ = ['Context']
 
-Context: BaseRuntimeContext = None
+Context: typing.Union[BaseRuntimeContext, None] = None
 
 try:
     from .async_context import AsyncRuntimeContext
diff --git a/opentelemetry-api/src/opentelemetry/context/async_context.py b/opentelemetry-api/src/opentelemetry/context/async_context.py
index 614cfaacc0d..6e5f0c0fce3 100644
--- a/opentelemetry-api/src/opentelemetry/context/async_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/async_context.py
@@ -12,23 +12,24 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import contextvars
+from contextvars import ContextVar
+import typing
 
 from .base_context import BaseRuntimeContext
 
 
 class AsyncRuntimeContext(BaseRuntimeContext):
     class Slot(BaseRuntimeContext.Slot):
-        def __init__(self, name, default):
+        def __init__(self, name: str, default: typing.Any):
             # pylint: disable=super-init-not-called
             self.name = name
-            self.contextvar = contextvars.ContextVar(name)
+            self.contextvar: typing.Any = ContextVar(name)
             self.default = default if callable(default) else (lambda: default)
 
-        def clear(self):
+        def clear(self) -> None:
             self.contextvar.set(self.default())
 
-        def get(self):
+        def get(self) -> typing.Any:
             try:
                 return self.contextvar.get()
             except LookupError:
@@ -36,5 +37,5 @@ def get(self):
                 self.set(value)
                 return value
 
-        def set(self, value):
+        def set(self, value: typing.Any) -> None:
             self.contextvar.set(value)
diff --git a/opentelemetry-api/src/opentelemetry/context/base_context.py b/opentelemetry-api/src/opentelemetry/context/base_context.py
index 67d42a10b49..5cc1794cd06 100644
--- a/opentelemetry-api/src/opentelemetry/context/base_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/base_context.py
@@ -60,7 +60,7 @@ def register_slot(cls, name: str, default: typing.Any = None) -> 'Slot':
             cls._slots[name] = slot
             return slot
 
-    def apply(self, snapshot) -> None:
+    def apply(self, snapshot: typing.Dict[str, typing.Any]) -> None:
         """Set the current context from a given snapshot dictionary"""
 
         for name in snapshot:
@@ -75,24 +75,31 @@ def snapshot(self) -> typing.Dict[str, typing.Any]:
     def __repr__(self) -> str:
         return '{}({})'.format(type(self).__name__, self.snapshot())
 
-    def __getattr__(self, name) -> typing.Any:
+    def __getattr__(self, name: str) -> typing.Any:
         if name not in self._slots:
             self.register_slot(name, None)
         slot = self._slots[name]
         return slot.get()
 
-    def __setattr__(self, name, value) -> None:
+    def __setattr__(self, name: str, value: typing.Any) -> None:
         if name not in self._slots:
             self.register_slot(name, None)
         slot = self._slots[name]
         slot.set(value)
 
-    def with_current_context(self, func: typing.Callable) -> typing.Callable:
-        """Capture the current context and apply it to the provided func"""
+    def with_current_context(
+            self,
+            func: typing.Callable[..., typing.Any],
+        ) -> typing.Callable[..., typing.Any]:
+        """Capture the current context and apply it to the provided func.
+        """
 
         caller_context = self.snapshot()
 
-        def call_with_current_context(*args, **kwargs) -> typing.Any:
+        def call_with_current_context(
+                *args: typing.Any,
+                **kwargs: typing.Any,
+            ) -> typing.Any:
             try:
                 backup_context = self.snapshot()
                 self.apply(caller_context)
diff --git a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
index 9830aa83b03..25f07c98069 100644
--- a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import threading
+import typing
 
 from .base_context import BaseRuntimeContext
 
@@ -21,15 +22,15 @@ class ThreadLocalRuntimeContext(BaseRuntimeContext):
     class Slot(BaseRuntimeContext.Slot):
         _thread_local = threading.local()
 
-        def __init__(self, name, default):
+        def __init__(self, name: str, default: typing.Any):
             # pylint: disable=super-init-not-called
             self.name = name
             self.default = default if callable(default) else (lambda: default)
 
-        def clear(self):
+        def clear(self) -> None:
             setattr(self._thread_local, self.name, self.default())
 
-        def get(self):
+        def get(self) -> typing.Any:
             try:
                 return getattr(self._thread_local, self.name)
             except AttributeError:
@@ -37,5 +38,5 @@ def get(self):
                 self.set(value)
                 return value
 
-        def set(self, value):
+        def set(self, value: typing.Any) -> None:
             setattr(self._thread_local, self.name, value)

From 1f93a36b5786112cce8ac5c3c0b7b4d92ac8a6c1 Mon Sep 17 00:00:00 2001
From: Chris Kleinknecht <libc@google.com>
Date: Fri, 19 Jul 2019 10:10:42 -0700
Subject: [PATCH 18/20] Type hint edits for #57 (#59)

---
 mypy-relaxed.ini                              |  2 +-
 mypy.ini                                      |  2 +-
 .../src/opentelemetry/context/__init__.py     |  4 ++-
 .../opentelemetry/context/async_context.py    | 19 +++++------
 .../src/opentelemetry/context/base_context.py | 32 +++++++++++--------
 .../context/thread_local_context.py           | 18 ++++++-----
 6 files changed, 44 insertions(+), 33 deletions(-)

diff --git a/mypy-relaxed.ini b/mypy-relaxed.ini
index 9cd56789a1e..205688353e3 100644
--- a/mypy-relaxed.ini
+++ b/mypy-relaxed.ini
@@ -3,7 +3,7 @@
 [mypy]
   disallow_any_unimported = True
 ; disallow_any_expr = True
-; disallow_any_decorated = True
+  disallow_any_decorated = True
 ; disallow_any_explicit = True
   disallow_any_generics = True
   disallow_subclassing_any = True
diff --git a/mypy.ini b/mypy.ini
index abb7aba2961..ba375b62b1d 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,7 +1,7 @@
 [mypy]
   disallow_any_unimported = True
   disallow_any_expr = True
-; disallow_any_decorated = True
+  disallow_any_decorated = True
 ; disallow_any_explicit = True
   disallow_any_generics = True
   disallow_subclassing_any = True
diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index c2fe840cb44..db975f9e510 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -16,9 +16,11 @@
 
 from .base_context import BaseRuntimeContext
 
+
 __all__ = ['Context']
 
-Context: typing.Union[BaseRuntimeContext, None] = None
+
+Context: typing.Optional[BaseRuntimeContext]
 
 try:
     from .async_context import AsyncRuntimeContext
diff --git a/opentelemetry-api/src/opentelemetry/context/async_context.py b/opentelemetry-api/src/opentelemetry/context/async_context.py
index 6e5f0c0fce3..f118870ecea 100644
--- a/opentelemetry-api/src/opentelemetry/context/async_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/async_context.py
@@ -12,24 +12,25 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from contextvars import ContextVar
 import typing
+from contextvars import ContextVar
 
-from .base_context import BaseRuntimeContext
+from . import base_context
 
 
-class AsyncRuntimeContext(BaseRuntimeContext):
-    class Slot(BaseRuntimeContext.Slot):
-        def __init__(self, name: str, default: typing.Any):
+class AsyncRuntimeContext(base_context.BaseRuntimeContext):
+    class Slot(base_context.BaseRuntimeContext.Slot):
+        def __init__(self, name: str, default: 'object'):
             # pylint: disable=super-init-not-called
             self.name = name
-            self.contextvar: typing.Any = ContextVar(name)
-            self.default = default if callable(default) else (lambda: default)
+            self.contextvar: 'ContextVar[object]' = ContextVar(name)
+            self.default: typing.Callable[..., object]
+            self.default = base_context.wrap_callable(default)
 
         def clear(self) -> None:
             self.contextvar.set(self.default())
 
-        def get(self) -> typing.Any:
+        def get(self) -> 'object':
             try:
                 return self.contextvar.get()
             except LookupError:
@@ -37,5 +38,5 @@ def get(self) -> typing.Any:
                 self.set(value)
                 return value
 
-        def set(self, value: typing.Any) -> None:
+        def set(self, value: 'object') -> None:
             self.contextvar.set(value)
diff --git a/opentelemetry-api/src/opentelemetry/context/base_context.py b/opentelemetry-api/src/opentelemetry/context/base_context.py
index 5cc1794cd06..35ee179a4b8 100644
--- a/opentelemetry-api/src/opentelemetry/context/base_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/base_context.py
@@ -16,18 +16,24 @@
 import typing
 
 
+def wrap_callable(target: 'object') -> typing.Callable[[], object]:
+    if callable(target):
+        return target
+    return lambda: target
+
+
 class BaseRuntimeContext:
     class Slot:
-        def __init__(self, name: str, default: typing.Any):
+        def __init__(self, name: str, default: 'object'):
             raise NotImplementedError
 
         def clear(self) -> None:
             raise NotImplementedError
 
-        def get(self) -> typing.Any:
+        def get(self) -> 'object':
             raise NotImplementedError
 
-        def set(self, value: typing.Any) -> None:
+        def set(self, value: 'object') -> None:
             raise NotImplementedError
 
     _lock = threading.Lock()
@@ -42,7 +48,7 @@ def clear(cls) -> None:
             slot.clear()
 
     @classmethod
-    def register_slot(cls, name: str, default: typing.Any = None) -> 'Slot':
+    def register_slot(cls, name: str, default: 'object' = None) -> 'Slot':
         """Register a context slot with an optional default value.
 
         :type name: str
@@ -60,13 +66,13 @@ def register_slot(cls, name: str, default: typing.Any = None) -> 'Slot':
             cls._slots[name] = slot
             return slot
 
-    def apply(self, snapshot: typing.Dict[str, typing.Any]) -> None:
+    def apply(self, snapshot: typing.Dict[str, 'object']) -> None:
         """Set the current context from a given snapshot dictionary"""
 
         for name in snapshot:
             setattr(self, name, snapshot[name])
 
-    def snapshot(self) -> typing.Dict[str, typing.Any]:
+    def snapshot(self) -> typing.Dict[str, 'object']:
         """Return a dictionary of current slots by reference."""
 
         keys = self._slots.keys()
@@ -75,13 +81,13 @@ def snapshot(self) -> typing.Dict[str, typing.Any]:
     def __repr__(self) -> str:
         return '{}({})'.format(type(self).__name__, self.snapshot())
 
-    def __getattr__(self, name: str) -> typing.Any:
+    def __getattr__(self, name: str) -> 'object':
         if name not in self._slots:
             self.register_slot(name, None)
         slot = self._slots[name]
         return slot.get()
 
-    def __setattr__(self, name: str, value: typing.Any) -> None:
+    def __setattr__(self, name: str, value: 'object') -> None:
         if name not in self._slots:
             self.register_slot(name, None)
         slot = self._slots[name]
@@ -89,17 +95,17 @@ def __setattr__(self, name: str, value: typing.Any) -> None:
 
     def with_current_context(
             self,
-            func: typing.Callable[..., typing.Any],
-        ) -> typing.Callable[..., typing.Any]:
+            func: typing.Callable[..., 'object'],
+    ) -> typing.Callable[..., 'object']:
         """Capture the current context and apply it to the provided func.
         """
 
         caller_context = self.snapshot()
 
         def call_with_current_context(
-                *args: typing.Any,
-                **kwargs: typing.Any,
-            ) -> typing.Any:
+                *args: 'object',
+                **kwargs: 'object',
+        ) -> 'object':
             try:
                 backup_context = self.snapshot()
                 self.apply(caller_context)
diff --git a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
index 25f07c98069..dd11128b7ac 100644
--- a/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/thread_local_context.py
@@ -15,28 +15,30 @@
 import threading
 import typing
 
-from .base_context import BaseRuntimeContext
+from . import base_context
 
 
-class ThreadLocalRuntimeContext(BaseRuntimeContext):
-    class Slot(BaseRuntimeContext.Slot):
+class ThreadLocalRuntimeContext(base_context.BaseRuntimeContext):
+    class Slot(base_context.BaseRuntimeContext.Slot):
         _thread_local = threading.local()
 
-        def __init__(self, name: str, default: typing.Any):
+        def __init__(self, name: str, default: 'object'):
             # pylint: disable=super-init-not-called
             self.name = name
-            self.default = default if callable(default) else (lambda: default)
+            self.default: typing.Callable[..., object]
+            self.default = base_context.wrap_callable(default)
 
         def clear(self) -> None:
             setattr(self._thread_local, self.name, self.default())
 
-        def get(self) -> typing.Any:
+        def get(self) -> 'object':
             try:
-                return getattr(self._thread_local, self.name)
+                got: object = getattr(self._thread_local, self.name)
+                return got
             except AttributeError:
                 value = self.default()
                 self.set(value)
                 return value
 
-        def set(self, value: typing.Any) -> None:
+        def set(self, value: 'object') -> None:
             setattr(self._thread_local, self.name, value)

From 0b114e40d647ee919f6dd7301fb058fbf055978e Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Fri, 19 Jul 2019 10:30:31 -0700
Subject: [PATCH 19/20] fix import order

---
 opentelemetry-api/src/opentelemetry/context/__init__.py      | 1 -
 opentelemetry-api/src/opentelemetry/context/async_context.py | 2 +-
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index db975f9e510..d902d866b6b 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -16,7 +16,6 @@
 
 from .base_context import BaseRuntimeContext
 
-
 __all__ = ['Context']
 
 
diff --git a/opentelemetry-api/src/opentelemetry/context/async_context.py b/opentelemetry-api/src/opentelemetry/context/async_context.py
index f118870ecea..413e7b2543f 100644
--- a/opentelemetry-api/src/opentelemetry/context/async_context.py
+++ b/opentelemetry-api/src/opentelemetry/context/async_context.py
@@ -12,8 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import typing
 from contextvars import ContextVar
+import typing
 
 from . import base_context
 

From e557afd2e3c8ce2f2191aefb364affcc1668020b Mon Sep 17 00:00:00 2001
From: Reiley Yang <reyang@microsoft.com>
Date: Thu, 25 Jul 2019 18:09:57 -0700
Subject: [PATCH 20/20] add module doc and example

---
 .../src/opentelemetry/context/__init__.py     | 125 ++++++++++++++++++
 1 file changed, 125 insertions(+)

diff --git a/opentelemetry-api/src/opentelemetry/context/__init__.py b/opentelemetry-api/src/opentelemetry/context/__init__.py
index d902d866b6b..a02bc8cb4e2 100644
--- a/opentelemetry-api/src/opentelemetry/context/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/context/__init__.py
@@ -12,6 +12,131 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+
+"""
+The OpenTelemetry context module provides abstraction layer on top of
+thread-local storage and contextvars. The long term direction is to switch to
+contextvars provided by the Python runtime library.
+
+A global object ``Context`` is provided to access all the context related
+functionalities:
+
+    >>> from opentelemetry.context import Context
+    >>> Context.foo = 1
+    >>> Context.foo = 2
+    >>> Context.foo
+    2
+
+When explicit thread is used, a helper function `Context.with_current_context`
+can be used to carry the context across threads:
+
+    from threading import Thread
+    from opentelemetry.context import Context
+
+    def work(name):
+        print('Entering worker:', Context)
+        Context.operation_id = name
+        print('Exiting worker:', Context)
+
+    if __name__ == '__main__':
+        print('Main thread:', Context)
+        Context.operation_id = 'main'
+
+        print('Main thread:', Context)
+
+        # by default context is not propagated to worker thread
+        thread = Thread(target=work, args=('foo',))
+        thread.start()
+        thread.join()
+
+        print('Main thread:', Context)
+
+        # user can propagate context explicitly
+        thread = Thread(
+            target=Context.with_current_context(work),
+            args=('bar',),
+        )
+        thread.start()
+        thread.join()
+
+        print('Main thread:', Context)
+
+Here goes another example using thread pool:
+
+    import time
+    import threading
+
+    from multiprocessing.dummy import Pool as ThreadPool
+    from opentelemetry.context import Context
+
+    _console_lock = threading.Lock()
+
+    def println(msg):
+        with _console_lock:
+            print(msg)
+
+    def work(name):
+        println('Entering worker[{}]: {}'.format(name, Context))
+        Context.operation_id = name
+        time.sleep(0.01)
+        println('Exiting worker[{}]: {}'.format(name, Context))
+
+    if __name__ == "__main__":
+        println('Main thread: {}'.format(Context))
+        Context.operation_id = 'main'
+        pool = ThreadPool(2)  # create a thread pool with 2 threads
+        pool.map(Context.with_current_context(work), [
+            'bear',
+            'cat',
+            'dog',
+            'horse',
+            'rabbit',
+        ])
+        pool.close()
+        pool.join()
+        println('Main thread: {}'.format(Context))
+
+Here goes a simple demo of how async could work in Python 3.7+:
+
+    import asyncio
+
+    from opentelemetry.context import Context
+
+    class Span(object):
+        def __init__(self, name):
+            self.name = name
+            self.parent = Context.current_span
+
+        def __repr__(self):
+            return ('{}(name={}, parent={})'
+                    .format(
+                        type(self).__name__,
+                        self.name,
+                        self.parent,
+                    ))
+
+        async def __aenter__(self):
+            Context.current_span = self
+
+        async def __aexit__(self, exc_type, exc, tb):
+            Context.current_span = self.parent
+
+    async def main():
+        print(Context)
+        async with Span('foo'):
+            print(Context)
+            await asyncio.sleep(0.1)
+            async with Span('bar'):
+                print(Context)
+                await asyncio.sleep(0.1)
+            print(Context)
+            await asyncio.sleep(0.1)
+        print(Context)
+
+    if __name__ == '__main__':
+        asyncio.run(main())
+"""
+
 import typing
 
 from .base_context import BaseRuntimeContext