Check that the handler for gevent.hub.signal is callable at construction time. Fixes #818.

changelog.rst

@@ -111,6 +111,9 @@ Other Changes
   while it's being read from or written to in a different greenlet is
   less likely to raise a :exc:`TypeError` instead of a
   :exc:`ValueError`. Reported in :issue:`800` by Kevin Chen.
+- :class:`gevent.hub.signal` (aka :func:`gevent.signal`) now verifies
+  that its `handler` argument is callable, raising a :exc:`TypeError`
+  if it isn't. Reported in :issue:`818` by Peter Renström.
 
 1.1.1 (Apr 4, 2016)
 ===================

doc/gevent.rst

@@ -175,6 +175,10 @@ Signals
          is replacing this name. This alias will be removed in a
          future release.
 
+    .. versionchanged:: 1.2a1
+
+          The *handler* is required to be callable at construction time.
+
 .. This is also in the docstring of gevent.hub.signal, which is the
    actual callable invoked
 

src/gevent/hub.py

@@ -228,6 +228,9 @@ class signal(object):
 
         This may not operate correctly with SIGCHLD if libev child watchers
         are used (as they are by default with os.fork).
+
+    .. versionchanged:: 1.2a1
+       The ``handler`` argument is required to be callable at construction time.
     """
 
     # XXX: This is manually documented in gevent.rst while it is aliased in
@@ -236,6 +239,9 @@ class signal(object):
     greenlet_class = None
 
     def __init__(self, signalnum, handler, *args, **kwargs):
+        if not callable(handler):
+            raise TypeError("signal handler must be callable.")
+
         self.hub = get_hub()
         self.watcher = self.hub.loop.signal(signalnum, ref=False)
         self.watcher.start(self._start)

src/greentest/test__signal.py

@@ -18,6 +18,9 @@ if hasattr(signal, 'SIGALRM'):
         error_fatal = False
         __timeout__ = 5
 
+        def test_handler(self):
+            self.assertRaises(TypeError, gevent.signal, signal.SIGALRM, 1)
+
         def test_alarm(self):
             sig = gevent.signal(signal.SIGALRM, raise_Expected)
             assert sig.ref is False, repr(sig.ref)