jax-ml/jax · error · TypeError

Default value must be of type float, got {default} of type {

Error message

Default value must be of type float, got {default} of type {getattr(type(default), '__name__', type(default))}

What it means

float_state requires `default` to be a Python float; ints and strings are rejected (unlike the runtime parser, which accepts ints). Non-float defaults raise this TypeError at flag definition.

Source

Thrown at jax/_src/config.py:755

    update_thread_local_hook: Callable[[float | None], None] | None = None,
) -> State[float]:
  """Set up thread-local state and return a contextmanager for managing it.

  See docstring for ``bool_state``.

  Args:
    name: string, converted to lowercase to define the name of the config
      option (and absl flag). It is converted to uppercase to define the
      corresponding shell environment variable.
    default: default value.
    help: string, used to populate the flag help information as well as the
      docstring of the returned context manager.

  Returns:
    A contextmanager to control the thread-local state value.
  """
  if not isinstance(default, float):
    raise TypeError(f"Default value must be of type float, got {default} "
                    f"of type {getattr(type(default), '__name__', type(default))}")
  name = name.lower()
  default_env = os.getenv(name.upper())
  if default_env is not None:
    try:
      default = float(default_env)
    except ValueError:
      raise ValueError(f"Invalid value \"{default_env}\" for JAX flag {name}")
  config._contextmanager_flags.add(name)

  def parser(new_val):
    if new_val is not None and not isinstance(new_val, (float, int)):
      raise ValueError(
        f'new float config value must be None or of type float, '
        f'got {new_val} of type {type(new_val)}')
    return new_val

  s = State[float](name, default, help, update_global_hook,

View on GitHub (pinned to 1e1c6a8fc0)

Solutions

1. Add a decimal point: default=0.5 or default=float(value)
2. Wrap externally-sourced defaults with float(...)

Example fix

// before
config.float_state('my_flag', default=1)
// after
config.float_state('my_flag', default=1.0)

assert isinstance(default, float), 'default must be a Python float (write 1.0 not 1)'

def is_float(v) -> bool:
    return isinstance(v, float)

When it happens

Trigger: Calling config.float_state('my_flag', default=1) or default='0.5'.

Common situations: Defining a tolerance/learning-rate style flag and naturally writing default=0 (int) instead of 0.0.

Related errors

• bool() not supported for instances of type '{0}' (did you me
• Default value must be of type bool, got {default} of type {g
• Default value must be of type str, got {default} of type {ge
• Default value must be of type str or None, got {default} of
• Default value must be of type {enum_class}, got {default} of

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/70cb9c2088c81c9c. Report an issue: GitHub.