blinker.signal() and blinker.Namespace no longer use weak references.

In the original implementation, I was uneasy about releasing a library
that held an unbounded, module-level cache, so it was built using a
weak value mapping. In practice, users making tons of signals are
using Signal() directly, and the weak referencing violates the
principle of least surprise in code like `signal('foo').connect(...)`.

Previous code is available as WeakNamespace for the time being. The
implementation is trivial and will likely be dropped in the future
unless use cases are voiced.

1 files changed, 22 insertions, 1 deletions

diff --git a/blinker/base.py b/blinker/base.py
index 615ef77..d8fe9f7 100644
--- a/blinker/base.py
+++ b/blinker/base.py
@@ -387,7 +387,7 @@ class NamedSignal(Signal):
         return "%s; %r>" % (base[:-1], self.name)
 
 
-class Namespace(WeakValueDictionary):
+class Namespace(dict):
     """A mapping of signal names to signals."""
 
     def signal(self, name, doc=None):
@@ -402,4 +402,25 @@ class Namespace(WeakValueDictionary):
             return self.setdefault(name, NamedSignal(name, doc))
 
 
+class WeakNamespace(WeakValueDictionary):
+    """A weak mapping of signal names to signals.
+
+    Automatically cleans up unused Signals when the last reference goes out
+    of scope.  This namespace implementation exists for a measure of legacy
+    compatibility with Blinker <= 1.2, and may be dropped in the future.
+
+    """
+
+    def signal(self, name, doc=None):
+        """Return the :class:`NamedSignal` *name*, creating it if required.
+
+        Repeated calls to this function will return the same signal object.
+
+        """
+        try:
+            return self[name]
+        except KeyError:
+            return self.setdefault(name, NamedSignal(name, doc))
+
+
 signal = Namespace().signal