Your suggestion would work for many cases, but for example:

items = ‘1, 2, 3’ (using comma-space delimiters for readability)

yields:

>>> items
['1', '', '2', '', '3']

Similarly, if someone were using space delimiters and accidentally specified 2 consecutive spaces, an empty string would be produced. Empty strings might cause a problem with MTurk.

Also, my approach allows for any whitespace delimiters; not just spaces and commas. Perhaps the answer is to add an explanatory comment for the regex:

# convert string to array; if more than one token, support comma or whitespace separators.