NFC: Extract default key variable

[blarz]

No description provided.

[chca42]

There is a reason why I use key=None in this case (you can still extract the key as global variable, though): If a default argument in python is a mutable sequence, the instance passed in the function is only created once at startup and every function call receives exactly the same instance (default arguments are evaluated upon processing the function definition). Thus you must not modify this variable in this case. Since python does not allow defining this as constant, it is dangerous to assume this implicitly to prevent side effects if any code part passes this by reference somewhere and the key array is modified without being copied before. Since this behavior of python (which is exactly the way it is defined in the language specification, see https://docs.python.org/3/reference/compound_stmts.html#function-definitions at the paragraph "Default parameter values ...") is somewhat surprising, my personal feeling is to prevent anyone from running into this issue.

If you want to extract the key, my recommendation would be to copy the global variable into the argument with "xyz.copy()" if detected as None.

[blarz]

That makes sense, I did not think about that!
I updated the PR accordingly.

[chca42]

thx