If the signal.Signals enum is not present, search the dictionary.

The Signals enum was added in Python 3.5.  If it is not present we
need to iterate over the dictionary items, looking for signal name
to number mappings.  Fixes the signal tests with Python 3.4.

plugins/python/example_io_plugin.py

@@ -104,10 +104,7 @@ class SudoIOPlugin(sudo.Plugin):
         self._log("WINSIZE", "{}x{}".format(line, cols))
 
     def log_suspend(self, signo: int) -> int:
-        try:
-            signal_description = signal.Signals(signo).name
-        except (AttributeError, ValueError):
-            signal_description = "signal {}".format(signo)
+        signal_description = self._signal_name(signo)
 
         self._log("SUSPEND", signal_description)
 
@@ -139,3 +136,18 @@ class SudoIOPlugin(sudo.Plugin):
     def _log(self, type, message):
         print(type, message, file=self._log_file)
         return sudo.RC.ACCEPT
+
+    if hasattr(signal, "Signals"):
+        def _signal_name(cls, signo: int):
+            try:
+                return signal.Signals(signo).name
+            except ValueError:
+                return "signal {}".format(signo)
+    else:
+        def _signal_name(cls, signo: int):
+            for n, v in sorted(signal.__dict__.items()):
+                if v != signo:
+                    continue;
+                if n.startswith("SIG") and not n.startswith("SIG_"):
+                    return n
+            return "signal {}".format(signo)