grass.pydispatch: Fix or selectively ignore Flake8 (#1808)

* E722 do not use bare 'except' resolved by using Exception.
* E501 line too long resolved by doctest result simplification.
* Enable Flake8, ignore and document remaining issues

.flake8

@@ -128,6 +128,9 @@ per-file-ignores =
     gui/wxpython/rlisetup/wizard.py: E722, E741
     # Generated file
     gui/wxpython/menustrings.py: E501
+    # F821 undefined name 'cmp'
+    # https://github.com/OSGeo/grass/issues/1809
+    python/grass/pydispatch/saferef.py: F821
     # C wrappers call libgis.G_gisinit before importing other modules.
     # TODO: Is this really needed?
     python/grass/pygrass/vector/__init__.py: E402,
@@ -241,7 +244,6 @@ exclude =
     testreport,
     # Not yet compliant
     python/grass/ctypes,
-    python/grass/pydispatch,
     # No tests checked for now
     testsuite,
 

python/grass/pydispatch/dispatcher.py

@@ -158,7 +158,7 @@ def connect(receiver, signal=Any, sender=Any, weak=True):
         try:
             weakSender = weakref.ref(sender, remove)
             senders[senderkey] = weakSender
-        except:
+        except Exception:
             pass
 
     receiverID = id(receiver)
@@ -175,7 +175,7 @@ def connect(receiver, signal=Any, sender=Any, weak=True):
             sendersBack[receiverID] = current = []
         if senderkey not in current:
             current.append(senderkey)
-    except:
+    except Exception:
         pass
 
     receivers.append(receiver)
@@ -401,7 +401,7 @@ def _cleanupConnections(senderkey, signal):
     """Delete any empty signals for senderkey. Delete senderkey if empty."""
     try:
         receivers = connections[senderkey][signal]
-    except:
+    except Exception:
         pass
     else:
         if not receivers:
@@ -428,7 +428,7 @@ def _removeSender(senderkey):
     # could be weakly referenced.
     try:
         del senders[senderkey]
-    except:
+    except Exception:
         pass
 
 
@@ -489,7 +489,7 @@ def _killBackref(receiver, senderkey):
     while senderkey in set:
         try:
             set.remove(senderkey)
-        except:
+        except Exception:
             break
     if not set:
         try:

python/grass/pydispatch/signal.py

@@ -174,7 +174,7 @@ class Signal(object):
 
         >>> signal1.disconnect(sys.stdout.flush)  #doctest: +ELLIPSIS
         Traceback (most recent call last):
-        DispatcherKeyError: 'No receivers found for signal <__main__.Signal object at 0x...> from sender _Any'
+        DispatcherKeyError: 'No receivers found for signal ...'
 
         Disconnecting the non-exiting or unknown handler will result in error.