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I am trying to get into numba gpu processing . I have this MWE :

import numpy as np
import numba
@numba.njit
def function():
    ar = np.zeros((3, 3))
    for i in range(3):
        ar[i] = (1, 2, 3)
    return ar
ar = function()
print(ar)
Output:
[[1. 2. 3.]
 [1. 2. 3.]
 [1. 2. 3.]]
Now I want to run it on my gpu. I tried using following decorators:
@numba.njit(target='cuda')
@numba.njit(target='gpu')
@numba.cuda.jit
none of which work. Here are the error messages of above decorators:
Traceback (most recent call last):
  File "/home/amu/Desktop/RL_framework/help_functions/test.py", line 4, in <module>
    @numba.jit(target='cuda')
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/core/decorators.py", line 171, in jit
    targetoptions=options, **dispatcher_args)
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/core/decorators.py", line 179, in _jit
    dispatcher = registry.dispatcher_registry[target]
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/core/registry.py", line 96, in __getitem__
    return super(TargetRegistry, self).__getitem__(item)
KeyError: 'cuda'
Traceback (most recent call last):
  File "/home/amu/Desktop/RL_framework/help_functions/test.py", line 4, in <module>
    @numba.njit(target='gpu')
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/core/decorators.py", line 236, in njit
    return jit(*args, **kws)
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/core/decorators.py", line 171, in jit
    targetoptions=options, **dispatcher_args)
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/core/decorators.py", line 179, in _jit
    dispatcher = registry.dispatcher_registry[target]
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/core/registry.py", line 96, in __getitem__
    return super(TargetRegistry, self).__getitem__(item)
KeyError: 'gpu'
Traceback (most recent call last):
  File "/home/amu/Desktop/RL_framework/help_functions/test.py", line 4, in <module>
    @numba.cuda.jit()
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/__init__.py", line 140, in __getattr__
    ) from None
AttributeError: module 'numba' has no attribute 'cuda'
numba.cuda is not even recognized as module function. I have numba 49.1 and cudatoolkit 9.0 installed.
Do I have to change the function for this to work? I have a huge numba.njit function that I need to run on a gpu.
I was trying to learn more about numba's cuda implementation from:
http://numba.pydata.org/numba-doc/0.16.0/modules/numba.cuda.html
Thank you in advance.
Edit:
As @talonmies proposed I imported cuda explicitly from the numba module and outsourced the array creation:
import numpy as np
import numba
from numba import cuda
@numba.njit(target='cuda')
def function(ar=None):
    for i in range(3):
        ar[i] = (1, 2, 3)
    return ar
ar = np.zeros((3, 3))
ar_result = function(ar=ar)
print(ar_result)
Output:
Traceback (most recent call last):
  File "/home/amu/Desktop/RL_framework/help_functions/test.py", line 12, in <module>
    ar_result = function(ar=ar)
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/cuda/dispatcher.py", line 40, in __call__
    return self.compiled(*args, **kws)
TypeError: __call__() got an unexpected keyword argument 'ar'
This error occurs with every of the aforementioned decorators except @numba.njit.
Edit_2:
When I try to run:
import numpy as np
import numba
from numba import cuda
@numba.jit(target='cuda')
def function(ar):
    for i in range(3):
        ar[i] = (1,2,3)
ar = np.zeros((3, 3))
function(ar)
print(ar)
the output is:
Traceback (most recent call last):
  File "/home/amu/Desktop/RL_framework/help_functions/test.py", line 11, in <module>
    function(ar)
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/cuda/dispatcher.py", line 40, in __call__
    return self.compiled(*args, **kws)
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/cuda/compiler.py", line 758, in __call__
    kernel = self.specialize(*args)
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/cuda/compiler.py", line 769, in specialize
    kernel = self.compile(argtypes)
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/cuda/compiler.py", line 785, in compile
    **self.targetoptions)
  File "/home/amu/anaconda3/lib/python3.7/site-packages/numba/core/compiler_lock.py", line 32, in _acquire_compile_lock
    return func(*args, **kwargs)
TypeError: compile_kernel() got an unexpected keyword argument 'boundscheck'
                Array creation isn't supported on the GPU so your code won't work, but you need to explicitly import the cuda module from numba to get the cuda decorator or target
– talonmies
                Jul 8, 2020 at 12:08
                would it work if you create the arrays outside the numba decorated function and then pass them to the numba decorated function?
– Artur Müller Romanov
                Jul 8, 2020 at 12:15
                Would you like to answer your own question for future visitors with the same problem? I will happily upvote it
– talonmies
                Jul 8, 2020 at 12:22
                For your latest edit 2, this seems to be a known issue with recent versions of numba.  You may be able to work around it by changing the kernel launch from: function(ar) to function[1,1](ar) which is equivalent.
– Robert Crovella
                Jul 8, 2020 at 17:44
Three points:
You have to explicitly import the cuda module from numba to use it (this isn't specific to numba, all python libraries work like this)
The nopython mode (njit) doesn't support the CUDA target
Array creation, return values, keyword arguments are not supported in Numba for CUDA code
I can fix all that like this:
...: import numpy as np 
...: import numba 
...: from numba import cuda 
...: @numba.jit(target='cuda') 
...: def function(ar): 
...:     for i in range(3): 
...:         ar[i] = (1,2,3)   
...: ar = np.zeros((3, 3)) 
...: function(ar) 
...: print(ar) 
[[1. 2. 3.]
 [1. 2. 3.]
 [1. 2. 3.]]
        
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