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
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 __future__ import absolute_import
  from abc import ABCMeta, abstractmethod
  from collections import namedtuple
  from errno import EINTR
  import math
  import select
  import sys
  from kafka.vendor import six
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