Unique types for sentinel objects

Resolves python-hyper#8.

Author: RazerM

h11/_connection.py

@@ -6,7 +6,8 @@
 # Import all state sentinels
 from ._state import *
 # Import the internal things we need
-from ._util import LocalProtocolError, RemoteProtocolError, Sentinel
+from ._util import (
+    LocalProtocolError, RemoteProtocolError, Sentinel, make_sentinel)
 from ._state import ConnectionState, _SWITCH_UPGRADE, _SWITCH_CONNECT
 from ._headers import (
     get_comma_header, set_comma_header, has_expect_100_continue,
@@ -18,8 +19,8 @@
 # Everything in __all__ gets re-exported as part of the h11 public API.
 __all__ = ["Connection", "NEED_DATA", "PAUSED"]
 
-NEED_DATA = Sentinel("NEED_DATA")
-PAUSED = Sentinel("PAUSED")
+NEED_DATA = make_sentinel("NEED_DATA")
+PAUSED = make_sentinel("PAUSED")
 
 # If we ever have this much buffered without it making a complete parseable
 # event, we error out. The only time we really buffer is when reading the
@@ -418,7 +419,7 @@ def next_event(self):
                 "Can't receive data when peer state is ERROR")
         try:
             event = self._extract_next_receive_event()
-            if type(event) is not Sentinel:
+            if not isinstance(event, Sentinel):
                 self._process_event(self.their_role, event)
                 self._receive_buffer.compress()
             if event is NEED_DATA:

h11/_state.py

@@ -112,7 +112,7 @@
 # script to keep it in sync!
 
 from ._events import *
-from ._util import LocalProtocolError, Sentinel
+from ._util import LocalProtocolError, make_sentinel
 
 # Everything in __all__ gets re-exported as part of the h11 public API.
 __all__ = []
@@ -125,7 +125,7 @@
              # Switch types
              "_SWITCH_UPGRADE _SWITCH_CONNECT").split()
 for token in sentinels:
-    globals()[token] = Sentinel(token)
+    globals()[token] = make_sentinel(token)
 
 __all__ += [s for s in sentinels if not s.startswith("_")]
 

h11/_util.py

@@ -1,7 +1,7 @@
 import sys
 
 __all__ = ["ProtocolError", "LocalProtocolError", "RemoteProtocolError",
-           "validate", "Sentinel", "bytesify"]
+           "validate", "Sentinel", "bytesify", "make_sentinel"]
 
 class ProtocolError(Exception):
     """Exception indicating a violation of the HTTP/1.1 protocol.
@@ -91,14 +91,29 @@ def validate(regex, data, msg="malformed data"):
         raise LocalProtocolError(msg)
     return match.groupdict()
 
-# Sentinel values
-# Inherits identity-based comparison and hashing from object
 class Sentinel(object):
-    def __init__(self, name):
-        self._name = name
+    """Sentinel type for constructed sentinel types to inherit from.
+
+    The class inherits identity-based comparison and hashing from object.
+    """
+
+def make_sentinel(name):
+    """Return a sentinel value of a newly constructed type.
+
+    The constructed class is equivalent to the following:
+
+    .. code-block:: python
+
+        class <name>(object):
+            def __repr__(self):
+                return <name>
+    """
 
     def __repr__(self):
-        return self._name
+        return name
+
+    cls = type(name, (Sentinel,), dict(__repr__=__repr__))
+    return cls()
 
 # Used for methods, request targets, HTTP versions, header names, and header
 # values. Accepts ascii-strings, or bytes/bytearray/memoryview/..., and always

h11/tests/test_util.py

@@ -53,9 +53,11 @@ def test_validate():
     with pytest.raises(LocalProtocolError):
         validate(my_re, b"0.1\n")
 
-def test_Sentinel():
-    S = Sentinel("S")
+def test_make_sentinel():
+    S = make_sentinel("S")
     assert repr(S) == "S"
+    assert type(S).__name__ == "S"
+    assert isinstance(S, Sentinel)
     assert S == S
     assert S in {S}