class_docstr: Base selector implementation.
class_docstr_tok: ["Base","selector","implementation","."]
docstr: Return the key associated to a given file descriptor.
  
  Parameters:
  fd -- file descriptor
  
  Returns:
  corresponding key, or None if not found
docstr_tok: ["Return","the","key","associated","to","a","given","file","descriptor",".","Parameters",":","fd","--","file","descriptor","Returns",":","corresponding","key",",","or","None","if","not","found"]
code: 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
  
imports: from abc import ABCMeta, abstractmethod
  from collections import namedtuple
  from collections.abc import Mapping
  import math
  import select
  import sys
label_desc: Use image node_id 8 for calling the _BaseSelectorImpl obj's underlying member method code with example usage: obj._key_from_fd(fd) and returns: self, None