cirq.dirac_notation can't handle qudits when qid_shape is not passed in.

[vtomole]

How to reproduce the issue

import cirq
import numpy as np

state_vector = np.array([0, 0, 1], dtype=np.complex64)


print(cirq.dirac_notation(state_vector))
# prints
# 0

The correct result should be

|2⟩

Cirq version
main branch version

[jeeva2812]

Isn't printing 0 the expected behaviour, given that dirac_notation is considered it to be a qubit unless qid_shape is explicitly mentioned - Code Pointer

We could give a warning when the shape is not a power of 2, when qid_shape is not provided. On that note, there could be an error handling in place when the provide qid_shape and state vector is not compatible as well. Thoughts?

[vtomole]

Isn't printing 0 the expected behaviour, given that dirac_notation is considered it to be a qubit unless qid_shape is explicitly mentioned

Ah, yes i didn't know you could pass in qid_shape. I thought cirq.dirac_notation should be able to figure it out on it's own but now that i think about it, this doesn't seem likely.

We could give a warning when the shape is not a power of 2, when qid_shape is not provided.

Yep

On that note, there could be an error handling in place when the provide qid_shape and state vector is not compatible as well. Thoughts?

👍

[jeeva2812]

Sent out a pull request for handling this #6179