Typing (numpy.typing
)¶
Warning
Some of the types in this module rely on features only present in the standard library in Python 3.8 and greater. If you want to use these types in earlier versions of Python, you should install the typingextensions package.
Large parts of the NumPy API have PEP484style type annotations. In addition a number of type aliases are available to users, most prominently the two below:
ArrayLike
: objects that can be converted to arraysDTypeLike
: objects that can be converted to dtypes
Differences from the runtime NumPy API¶
NumPy is very flexible. Trying to describe the full range of possibilities statically would result in types that are not very helpful. For that reason, the typed NumPy API is often stricter than the runtime NumPy API. This section describes some notable differences.
ArrayLike¶
The ArrayLike
type tries to avoid creating object arrays. For
example,
>>> np.array(x**2 for x in range(10))
array(<generator object <genexpr> at ...>, dtype=object)
is valid NumPy code which will create a 0dimensional object
array. Type checkers will complain about the above example when using
the NumPy types however. If you really intended to do the above, then
you can either use a # type: ignore
comment:
>>> np.array(x**2 for x in range(10)) # type: ignore
or explicitly type the array like object as Any
:
>>> from typing import Any
>>> array_like: Any = (x**2 for x in range(10))
>>> np.array(array_like)
array(<generator object <genexpr> at ...>, dtype=object)
ndarray¶
It’s possible to mutate the dtype of an array at runtime. For example, the following code is valid:
>>> x = np.array([1, 2])
>>> x.dtype = np.bool_
This sort of mutation is not allowed by the types. Users who want to
write statically typed code should insted use the numpy.ndarray.view
method to create a view of the array with a different dtype.
DTypeLike¶
The DTypeLike
type tries to avoid creation of dtype objects using
dictionary of fields like below:
>>> x = np.dtype({"field1": (float, 1), "field2": (int, 3)})
Although this is valid Numpy code, the type checker will complain about it, since its usage is discouraged. Please see : Data type objects
Number Precision¶
The precision of numpy.number
subclasses is treated as a covariant generic
parameter (see NBitBase
), simplifying the annoting of proccesses
involving precisionbased casting.
>>> from typing import TypeVar
>>> import numpy as np
>>> import numpy.typing as npt
>>> T = TypeVar("T", bound=npt.NBitBase)
>>> def func(a: "np.floating[T]", b: "np.floating[T]") > "np.floating[T]":
... ...
Consequently, the likes of float16
, float32
and
float64
are still subtypes of floating
, but, contrary to
runtime, they’re not necessarily considered as subclasses.
Timedelta64¶
The timedelta64
class is not considered a subclass of signedinteger
,
the former only inheriting from generic
while static type checking.
API¶

numpy.typing.
ArrayLike
= typing.Union[...]¶ A
Union
representing objects that can be coerced into anndarray
.Among others this includes the likes of:
Scalars.
(Nested) sequences.
Objects implementing the __array__ protocol.
See Also
 array_like:
Any scalar or sequence that can be interpreted as an ndarray.
Examples
>>> import numpy as np >>> import numpy.typing as npt >>> def as_array(a: npt.ArrayLike) > np.ndarray: ... return np.array(a)

numpy.typing.
DTypeLike
= typing.Union[...]¶ A
Union
representing objects that can be coerced into adtype
.Among others this includes the likes of:
See Also
 Specifying and constructing data types
A comprehensive overview of all objects that can be coerced into data types.
Examples
>>> import numpy as np >>> import numpy.typing as npt >>> def as_dtype(d: npt.DTypeLike) > np.dtype: ... return np.dtype(d)

class
numpy.typing.
NBitBase
[source]¶ An object representing
numpy.number
precision during static type checking.Used exclusively for the purpose static type checking,
NBitBase
represents the base of a hierachieral set of subclasses. Each subsequent subclass is herein used for representing a lower level of precision, e.g.64Bit > 32Bit > 16Bit
.Examples
Below is a typical usage example:
NBitBase
is herein used for annotating a function that takes a float and integer of arbitrary precision as arguments and returns a new float of whichever precision is largest (e.g.np.float16 + np.int64 > np.float64
).>>> from typing import TypeVar, TYPE_CHECKING >>> import numpy as np >>> import numpy.typing as npt >>> T = TypeVar("T", bound=npt.NBitBase) >>> def add(a: "np.floating[T]", b: "np.integer[T]") > "np.floating[T]": ... return a + b >>> a = np.float16() >>> b = np.int64() >>> out = add(a, b) >>> if TYPE_CHECKING: ... reveal_locals() ... # note: Revealed local types are: ... # note: a: numpy.floating[numpy.typing._16Bit*] ... # note: b: numpy.signedinteger[numpy.typing._64Bit*] ... # note: out: numpy.floating[numpy.typing._64Bit*]