docs: def get_one(self, section, key):
          """Retrieve the first value for a section/key.
  
          Raises:
              KeyError: If no line match the given section/key.
          """
          lines = iter(self.get(section, key))
          try:
              return next(lines)
          except StopIteration:
              raise KeyError("Key %s not found in %s" % (key, section))