backport of bpo-30624 / PR #2082 for python 3.6

Author: giampaolo

Lib/selectors.py

@@ -410,7 +410,7 @@ def register(self, fileobj, events, data=None):
                 epoll_events |= select.EPOLLOUT
             try:
                 self._epoll.register(key.fd, epoll_events)
-            except BaseException:
+            except:
                 super().unregister(fileobj)
                 raise
             return key
@@ -543,7 +543,7 @@ def register(self, fileobj, events, data=None):
                     kev = select.kevent(key.fd, select.KQ_FILTER_WRITE,
                                         select.KQ_EV_ADD)
                     self._kqueue.control([kev], 0, 0)
-            except BaseException:
+            except:
                 super().unregister(fileobj)
                 raise
             return key

Misc/NEWS

@@ -49,6 +49,10 @@ Core and Builtins
 Library
 -------
 
+- bpo-30624: selectors does not take KeyboardInterrupt and SystemExit into
+  account, leaving a fd in a bad state in case of error. Patch by Giampaolo
+  Rodola'.
+
 - bpo-28556: Updates to typing module: Add generic AsyncContextManager, add
   support for ContextManager on all versions. Original PRs by Jelle Zijlstra
   and Ivan Levkivskyi