Dictionary keys cannot be CuPy element

A more answerable question would be, can keys of a dictionary be an element stored in GPU?

• Code to reproduce

import numpy as np
import cupy as cp

arr = [1, 2, 3]
np_dict = dict()
cp_dict = dict()
np_arr = np.asarray(arr)
cp_arr = cp.asarray(arr)

for i in np_arr:
     np_dict[i] = "okay"

print(np_dict)                                # {1: 'okay', 2: 'okay', 3: 'okay'}

for i in cp_arr:
     cp_dict[i] = "okay"

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
TypeError: unhashable type: 'cupy.core.core.ndarray'

• Error messages, stack traces, or logs Conditions (you can just paste the output of python -c 'import cupy; cupy.show_config()')

CuPy Version          : 6.0.0
CUDA Root             : /usr/local/cuda
CUDA Build Version    : 10000
CUDA Driver Version   : 11010
CUDA Runtime Version  : 10000
cuDNN Build Version   : 7301
cuDNN Version         : 7605
NCCL Build Version    : 1000
NCCL Runtime Version  : (unknown)

[aitikgupta]

Thanks! 👍🏼

[kmaehashi]

Unlike NumPy, CuPy returns a ndarray when iterating over a ndarray, even if the resulting value is a scalar. This is because the scalar value is on GPU and we don’t want to implicitly transfer it to the host (CPU) memory. You can use ndarray.item() to explicly convert the ndarray (cupy or numpy) into a scalar, e.g., cp_dict[i.item()] = "okay" instead of cp_dict[i] = "okay". https://docs.cupy.dev/en/stable/reference/generated/cupy.ndarray.html#cupy.ndarray.item