gh-106554: Replace _BaseSelectorImpl._key_from_fd with a simple get

Lib/selectors.py

@@ -272,19 +272,6 @@ def close(self):
     def get_map(self):
         return self._map
 
-    def _key_from_fd(self, fd):
-        """Return the key associated to a given file descriptor.
-
-        Parameters:
-        fd -- file descriptor
-
-        Returns:
-        corresponding key, or None if not found
-        """
-        try:
-            return self._fd_to_key[fd]
-        except KeyError:
-            return None
 
 
 class SelectSelector(_BaseSelectorImpl):
@@ -332,7 +319,7 @@ def select(self, timeout=None):
             if fd in w:
                 events |= EVENT_WRITE
 
-            key = self._key_from_fd(fd)
+            key = self._fd_to_key.get(fd)
             if key:
                 ready.append((key, events & key.events))
         return ready
@@ -422,7 +409,7 @@ def select(self, timeout=None):
             if event & ~self._EVENT_WRITE:
                 events |= EVENT_READ
 
-            key = self._key_from_fd(fd)
+            key = self._fd_to_key.get(fd)
             if key:
                 ready.append((key, events & key.events))
         return ready
@@ -475,7 +462,7 @@ def select(self, timeout=None):
                 if event & ~select.EPOLLOUT:
                     events |= EVENT_READ
 
-                key = self._key_from_fd(fd)
+                key = self._fd_to_key.get(fd)
                 if key:
                     ready.append((key, events & key.events))
             return ready
@@ -570,7 +557,7 @@ def select(self, timeout=None):
                 if flag == select.KQ_FILTER_WRITE:
                     events |= EVENT_WRITE
 
-                key = self._key_from_fd(fd)
+                key = self._fd_to_key.get(fd)
                 if key:
                     ready.append((key, events & key.events))
             return ready

Misc/NEWS.d/next/Library/2023-07-09-01-59-24.gh-issue-106554.37c53J.rst

@@ -0,0 +1 @@
+:mod:`selectors`: Reduce Selector overhead by using a ``dict.get()`` to lookup file descriptors.