jax-ml/jax · error · ValueError

dtype cannot be None.

Error message

dtype cannot be None.

What it means

jax.dtypes.itemsize_bits requires a concrete dtype; passing None (typically a dtype field that was never populated) is rejected because there is no meaningful bit width.

Source

Thrown at jax/_src/dtypes.py:287

  elif issubdtype(obj, extended):
    return obj  # pyrefly: ignore[bad-return]
  elif isinstance(obj, type) and (f := _DEFAULT_TYPEMAP.get(obj)) is not None:
    obj = f()
  return np.dtype(obj, align=align, copy=copy)

_DEFAULT_TYPEMAP: dict[type, Callable[[], np.dtype]] = {
  bool: lambda: np.dtype(bool),
  int: default_int_dtype,
  float: default_float_dtype,
  complex: default_complex_dtype,
}

def itemsize_bits(dtype: DTypeLike) -> int:
  """Number of bits per element for the dtype."""
  # Note: we cannot use dtype.itemsize here because this is
  # incorrect for sub-byte integer types.
  if dtype is None:
    raise ValueError("dtype cannot be None.")
  if dtype == np.dtype(bool):
    return 8  # physical bit layout for boolean dtype
  elif issubdtype(dtype, np.integer):
    return iinfo(dtype).bits
  elif issubdtype(dtype, np.floating):
    return finfo(dtype).bits
  elif issubdtype(dtype, np.complexfloating):
    return 2 * finfo(dtype).bits
  else:
    raise ValueError(f"unexpected input: {dtype=}")

# Trivial vectorspace datatype needed for tangent values of int/bool primals
float0: np.dtype = np.dtype([('float0', np.void, 0)])

_dtype_to_32bit_dtype: dict[DType, DType] = {
    np.dtype('int64'): np.dtype('int32'),
    np.dtype('uint64'): np.dtype('uint32'),
    np.dtype('float64'): np.dtype('float32'),

View on GitHub (pinned to 1e1c6a8fc0)

Solutions

1. Populate the dtype before the call (resolve defaults: `dtype = dtype or jnp.float32` if that is intended)
2. Add an assert dtype is not None upstream to fail fast with context
3. Fix the caller that dropped the dtype argument

Example fix

# before
itemsize_bits(x.dtype)  # x.dtype is None

# after
assert x.dtype is not None
itemsize_bits(x.dtype)

if dtype is None:
    raise ValueError('dtype required')
jax.dtypes.itemsize_bits(dtype)

When it happens

Trigger: Calling itemsize_bits(None) or threading a None dtype from config/shape-rule code (e.g. bitcast_convert_type with unset dtype) into this helper.

Common situations: Optional dtype parameters defaulting to None; partially-initialized dtypes in custom primitives or sharding rules calling _bitcast paths.

Related errors

• Expected a string or dtype-like object; got {dtype=}
• unexpected input: {dtype=}
• Unrecognized {kind=} expected one of {list(_dtype_kinds.keys
• Dtype {dtype} is not a valid JAX array type. Only arrays of
• Value '{x}' with dtype {dt} is not a valid JAX array type. O

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/087aa58363dedcf5. Report an issue: GitHub.