split string by arbitrary number of white spaces

How about:

re.split(r'\s+',string)

\s is short for any whitespace. So \s+ is a contiguous whitespace.

Just use my_str.split() without ' '.

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More, you can also indicate how many splits to perform by specifying the second parameter:

>>> ' 1 2 3 4  '.split(None, 2)
['1', '2', '3 4  ']
>>> ' 1 2 3 4  '.split(None, 1)
['1', '2 3 4  ']