message: Clarify what happens when a new value is input to some methods
diff: @@ -494,6 +494,7 @@ class HParams(object):
  value: New value of the hyperparameter.
  Raises:
  + KeyError: If the hyperparameter doesn't exist.
  ValueError: If there is a type mismatch.
  """
  param_type, is_list = self._hparam_types[name]
  @@ -510,7 +511,7 @@ class HParams(object):
  setattr(self, name, _cast_to_type_if_compatible(name, param_type, value))
  def del_hparam(self, name):
  - """Removes the hyperparameter with key 'name'.
  + """Removes the hyperparameter with key 'name'. Does nothing if it isn't present.
  Args:
  name: Name of the hyperparameter.
  @@ -532,7 +533,7 @@ class HParams(object):
  The `HParams` instance.
  Raises:
  - ValueError: If `values` cannot be parsed.
  + ValueError: If `values` cannot be parsed or a hyperparameter in `values` doesn't exist.
  """
  type_map = dict()
  for name, t in self._hparam_types.items():
  @@ -543,7 +544,7 @@ class HParams(object):
  return self.override_from_dict(values_map)
  def override_from_dict(self, values_dict):
  - """Override hyperparameter values, parsing new values from a dictionary.
  + """Override existing hyperparameter values, parsing new values from a dictionary.
  Args:
  values_dict: Dictionary of name:value pairs.
  @@ -552,6 +553,7 @@ class HParams(object):
  The `HParams` instance.
  Raises:
  + KeyError: If a hyperparameter in `values_dict` doesn't exist.
  ValueError: If `values_dict` cannot be parsed.
  """
  for name, value in values_dict.items():
  @@ -591,7 +593,7 @@ class HParams(object):
  sort_keys=sort_keys)
  def parse_json(self, values_json):
  - """Override hyperparameter values, parsing new values from a json object.
  + """Override existing hyperparameter values, parsing new values from a json object.
  Args:
  values_json: String containing a json object of name:value pairs.
  @@ -600,6 +602,7 @@ class HParams(object):
  The `HParams` instance.
  Raises:
  + KeyError: If a hyperparameter in `values_json` doesn't exist.
  ValueError: If `values_json` cannot be parsed.
  """
  values_map = json.loads(values_json)
  