# Numba OptionalType(array()) - Problems

**URL:** <https://numba.discourse.group/t/numba-optionaltype-array-problems/1925>\
**Category:** Support: What is this error message?\
**Created:** [May 5, 2023, 9:04am UTC](https://numba.discourse.group/t/numba-optionaltype-array-problems/1925 "2023-05-05T09:04:14Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![joueswant](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/joueswant/32/829_2.png) [@joueswant](https://numba.discourse.group/u/joueswant)\
**Post date:** [May 5, 2023, 9:04am UTC](https://numba.discourse.group/t/numba-optionaltype-array-problems/1925/1 "2023-05-05T09:04:14Z")

</div>

Hi there,  
I am developing a script using numba’s njit. I found myself stuck in a tricky situation. In overall terms, the funcs. giving the error look like the following:

```auto
@jit(nopython = True)
def dot_pred(a, b, c):
    return a @ np.linalg.inv(b) @ c.T

@jit(nopython = True)
def foo(maindim):
    aa = np.random.randn(maindim, 5)
    bb = np.random.randn(5,5)
    cc = np.random.randn(maindim, 5)
    # Call the problem func (njitted)
    out = dot_pred(aa, bb, cc)
    return out

```

Of course, these two funcs. work with Numba (as expected), but in my code (much more large) it does not… The error is the following:

```auto
TypingError: Failed in nopython mode pipeline (step: nopython frontend)
Failed in nopython mode pipeline (step: nopython frontend)
No implementation of function Function(\<function inv at 0x7ff7a8469f30>) found for signature:

> > > inv(OptionalType(array(float64, 2d, C)))

There are 2 candidate implementations:

- Of which 2 did not match due to:
Overload in function 'inv_impl': File: numba/np/linalg.py: Line 832.
With argument(s): '(OptionalType(array(float64, 2d, C)))':
Rejected as the implementation raised a specific error:
AttributeError: 'Optional' object has no attribute 'dtype'
raised from /home/xxxxxxxxxxxxx/python3.10/site-packages/numba/np/linalg.py:838

During: resolving callee type: Function(\<function inv at 0x7ff7a8469f30>)
During: typing of call at /tmp/ipykernel\_900007/3472101925.py (159)

```

To sum up,  
- The demo case with two funcs. (see above) works compiled with numba  
- My code works (results are ok and code is stable) without numba. Yet, when I njit I got the error above

The problem seems to be with the Optional() type and the ´dtype´ method that ´np.linalg.inv´ uses over the Optional type.

Any help on how to solve this, please?

Thanks a lot!

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<div class="post-metadata">

**Author:** ![Hannes](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/hannes/32/188_2.png) [@Hannes](https://numba.discourse.group/u/Hannes)\
**Post date:** [May 5, 2023, 12:48pm UTC](https://numba.discourse.group/t/numba-optionaltype-array-problems/1925/2 "2023-05-05T12:48:37Z")

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Hi @joueswant,

I get that you may shy away from sharing long code - but if you don’t show it (or better: narrow it down to the smallest failing unit and share that), it will be hard to help. If you are not allowed to share the code, then I understand that your hands may be tied. 😛

Anyway, in the docs we find [Glossary — Numba 0+untagged.4124.gd4460fe.dirty documentation](https://numba.readthedocs.io/en/stable/glossary.html#term-OptionalType) :

> `OptionalType`  
> An `OptionalType` is effectively a type union of a `type` and `None`. They typically occur in practice due to a variable being set to `None` and then in a branch the variable being set to some other value. It’s often not possible at compile time to determine if the branch will execute so to permit [type inference](https://numba.pydata.org/numba-doc/dev/glossary.html?highlight=optionaltype#term-type-inference) to complete, the type of the variable becomes the union of a `type` (from the value) and `None`, i.e. `OptionalType(type)`.

Together with the error context you received

> `> > > inv(OptionalType(array(float64, 2d, C)))`

we can assume that the problem is not with what inv uses or returns, but what you pass it: Under certain circumstances numba infers that the variable (presumably whatever gets passed to `b` of `dot_pred`) is `None`.

Possibly this won’t actually ever happen in your code due to checks you perform around the function call - but somewhere in the same scope a variable with the same name could become `None`. This can be enough to confuse the compiler. I think in simple cases this can be caught and inferred correctly by numba, but it depends on the exact context.

Maybe you can alleviate the problem by passing a variable to `dot_pred` that can never be None in any branch of your function.

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<div class="post-metadata">

**Author:** ![joueswant](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/joueswant/32/829_2.png) [@joueswant](https://numba.discourse.group/u/joueswant)\
**Post date:** [May 5, 2023, 3:15pm UTC](https://numba.discourse.group/t/numba-optionaltype-array-problems/1925/4 "2023-05-05T15:15:52Z")

</div>

I see, it is a mix between the None type defined in `subop2` and the try / except bug from here:  
[Confirm support for try/except use in objmode block · Issue #5377 · numba/numba (github.com)](https://github.com/numba/numba/issues/5377)

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<div class="post-metadata">

**Author:** ![joueswant](https://yyz2.discourse-cdn.com/free1/user_avatar/numba.discourse.group/joueswant/32/829_2.png) [@joueswant](https://numba.discourse.group/u/joueswant)\
**Post date:** [May 5, 2023, 3:31pm UTC](https://numba.discourse.group/t/numba-optionaltype-array-problems/1925/5 "2023-05-05T15:31:15Z")

</div>

Solved, thanks a lot @Hannes, the None type comes from a try except block, by passing a local variable instead of defining a temporal None type I solved the bug of the try/except and code runs smoothly and Justt in Time!

Thanks for your help!