Look at the example, your code needs to extend the key as needed. You've added the failsafe to encode, but not to decode method.

Why am I getting this error?

Traceback (most recent call last):
File "/workspace/default/.venv/lib/python3.11/site-packages/codewars_test/test_framework.py", line 112, in wrapper
func()
File "/workspace/default/tests.py", line 19, in it1
test.assert_equals(c.decode("xt'k o vwixl qzswej!"), "it's a shift cipher!")
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/workspace/default/solution.py", line 29, in decode
new_index = alphabet.index(text[i]) - alphabet.index(key[i])
~~~^^^
IndexError: string index out of range

Shouldn't the key be the same length as the text to encode, meaning that if text[i] exists then key[i] exists? I added a failsafe while loop:

while len(text) < len(key):
key = key + key

and still get the error. Thanks for any suggestions!

How am I supposed to handle multi-byte katakana, especially given that test cases are called with key="" alphabet=""?

And the fixes have been merged, thanks tor letting me know!

Should all be good now, thanks for the reports!

Here is a fork that addresses the issue; someone still needs to approve it though.

this is just beautiful...

MErged.

Confirmed; I published a fork to fix this.

Thanks for the report! I had based the generator on the C++ translation but I can see now that the alphabet selection is indeed incorrect. I'll see about getting this fixed ASAP.

Update: I published a fork with a fix, it just needs a review to go live.

Alphabets are now generated using sampling without replacement.

??
Whenever encode or decode is called, my code prints in order input string and output string..
I Will check.

but... doesnt explain the output auab^... of the expected value ??

can't verify due to not having solved in c++/not seeing your code
but - this looks to me like you're mixing up different test cases, ie. you're showing the input of one test and the expected output of a different one. be careful with how you print and how you read the output.

See above, Go tests seem to have a problem. I have tested some of them with my Python code and I get the same results as my Go code.

For instance:
Encode Key: OZzhEOAUlkOZDh Alpha: ckclVDAJzUsohOEJZQVDw Text: kZOlaAosDQbUE10FcO

My answer: EocJaDQDzVbVD10FzV Expected answer: EocJaDQDkVbVh10FsV

Haha, I just came here to say something is wrong with the Go tests.