Fix #805. Make reload(site) work w/gevent imported

Python 2 issue only.

Allow setting attributes on sys.modules['gevent.signal']; they go to the
gevent/signal.py module for symmetry with getattr and dir.

Reloading results in leaks so don't bother checking for them.

changelog.rst

@@ -68,7 +68,8 @@ Stdlib Compatibility
 - :meth:`gevent.select.poll.poll` returns an event with
   ``POLLNVAL`` for registered fds that are invalid. Previously it
   would tend to report both read and write events.
-
+- Python 2: ``reload(site)`` no longer fails with a ``TypeError`` if
+  gevent has been imported. Reported in :issue:`805` by Jake Hilton.
 
 Other Changes
 -------------
@@ -83,7 +84,8 @@ Other Changes
   timestamp. See :issue:`137`.
 - Add :class:`gevent.threadpool.ThreadPoolExecutor` (a
   :class:`concurrent.futures.ThreadPoolExecutor` variant that always
-  uses native threads) on platforms that have ``concurrent.futures``
+  uses native threads even when the system has been monkey-patched)
+  on platforms that have ``concurrent.futures``
   available (Python 3 and Python 2 with the ``futures`` backport
   installed). This is helpful for, e.g., grpc. Reported in
   :issue:`786` by Markus Padourek.

src/gevent/__init__.py

@@ -85,9 +85,10 @@ class _signal_metaclass(type):
         return getattr(_signal_module, name)
 
     def __setattr__(cls, name, value):
-        # Because we can't know whether to try to go to the module
-        # or the class, we don't allow setting an attribute after the fact
-        raise TypeError("Cannot set attribute")
+        # For symmetry with getattr and dir, pass all
+        # attribute setting on to the module. (This makes
+        # reloading work, see issue #805)
+        setattr(_signal_module, name, value)
 
     def __instancecheck__(cls, instance):
         return isinstance(instance, _signal_class)

src/greentest/greentest.py

@@ -58,13 +58,20 @@ PLATFORM_SPECIFIC_SUFFIXES = ['2', '279', '3']
 if sys.platform.startswith('win'):
     PLATFORM_SPECIFIC_SUFFIXES.append('posix')
 
+PY2 = None
+PY3 = None
+PY34 = None
+
 NON_APPLICABLE_SUFFIXES = []
 if sys.version_info[0] == 3:
     # Python 3
     NON_APPLICABLE_SUFFIXES.extend(('2', '279'))
     PY2 = False
     PY3 = True
-if sys.version_info[0] == 2:
+    if sys.version_info[1] >= 4:
+        PY34 = True
+
+elif sys.version_info[0] == 2:
     # Any python 2
     PY3 = False
     PY2 = True
@@ -73,6 +80,7 @@ if sys.version_info[0] == 2:
             or (sys.version_info[1] == 7 and sys.version_info[2] < 9)):
         # Python 2, < 2.7.9
         NON_APPLICABLE_SUFFIXES.append('279')
+
 if sys.platform.startswith('win'):
     NON_APPLICABLE_SUFFIXES.append("posix")
     # This is intimately tied to FileObjectPosix

src/greentest/test__signal.py

@@ -18,7 +18,7 @@ if hasattr(signal, 'SIGALRM'):
         error_fatal = False
         __timeout__ = 5
 
-        def test(self):
+        def test_alarm(self):
             sig = gevent.signal(signal.SIGALRM, raise_Expected)
             assert sig.ref is False, repr(sig.ref)
             sig.ref = True
@@ -41,6 +41,31 @@ if hasattr(signal, 'SIGALRM'):
             finally:
                 sig.cancel()
 
+        @greentest.ignores_leakcheck
+        def test_reload(self):
+            # The site module tries to set attributes
+            # on all the modules that are loaded (specifically, __file__).
+            # If gevent.signal is loaded, and is our compatibility shim,
+            # this used to fail on Python 2: sys.modules['gevent.signal'] has no
+            # __loader__ attribute, so site.py's main() function tries to do
+            # gevent.signal.__file__ = os.path.abspath(gevent.signal.__file__), which
+            # used to not be allowed. (Under Python 3, __loader__ is present so this
+            # doesn't happen). See
+            # https://github.com/gevent/gevent/issues/805
+
+            import gevent.signal # make sure it's in sys.modules pylint:disable=redefined-outer-name
+            assert gevent.signal
+            import site
+            if greentest.PY34:
+                from importlib import reload as reload_module
+            elif greentest.PY3:
+                from imp import reload as reload_module
+            else:
+                # builtin on py2
+                reload_module = reload # pylint:disable=undefined-variable
+
+            reload_module(site)
+
 
 if __name__ == '__main__':
     greentest.main()