## Question

Asked By – Inon

Has anyone implemented type hinting for the specific `numpy.ndarray`

class?

Right now, I’m using `typing.Any`

, but it would be nice to have something more specific.

For instance if the NumPy people added a type alias for their array_like object class. Better yet, implement support at the dtype level, so that other objects would be supported, as well as ufunc.

**Now we will see solution for issue: Type hinting / annotation (PEP 484) for numpy.ndarray **

## Answer

# Update

Check recent numpy versions for a new `typing`

module

https://numpy.org/doc/stable/reference/typing.html#module-numpy.typing

## dated answer

It looks like `typing`

module was developed at:

https://github.com/python/typing

The main `numpy`

repository is at

https://github.com/numpy/numpy

Python bugs and commits can be tracked at

The usual way of adding a feature is to fork the main repository, develop the feature till it is bomb proof, and then submit a pull request. Obviously at various points in the process you want feedback from other developers. If you can’t do the development yourself, then you have to convince someone else that it is a worthwhile project.

`cython`

has a form of annotations, which it uses to generate efficient `C`

code.

You referenced the `array-like`

paragraph in `numpy`

documentation. Note its `typing`

information:

A simple way to find out if the object can be converted to a numpy array using array() is simply to try it interactively and see if it works! (The Python Way).

In other words the `numpy`

developers refuse to be pinned down. They don’t, or can’t, describe in words what kinds of objects can or cannot be converted to `np.ndarray`

.

```
In [586]: np.array({'test':1}) # a dictionary
Out[586]: array({'test': 1}, dtype=object)
In [587]: np.array(['one','two']) # a list
Out[587]:
array(['one', 'two'],
dtype='<U3')
In [589]: np.array({'one','two'}) # a set
Out[589]: array({'one', 'two'}, dtype=object)
```

For your own functions, an annotation like

```
def foo(x: np.ndarray) -> np.ndarray:
```

works. Of course if your function ends up calling some `numpy`

function that passes its argument through `asanyarray`

(as many do), such an annotation would be incomplete, since your input could be a `list`

, or `np.matrix`

, etc.

When evaluating this question and answer, pay attention to the date. 484 was a relatively new PEP back then, and code to make use of it for standard Python still in development. But it looks like the links provided are still valid.

This question is answered By – hpaulj

**This answer is collected from stackoverflow and reviewed by FixPython community admins, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0 **