import re


def tokens(s):
    """Return a list of strings containing individual words from string s.

    This function splits on whitespace transitions, and captures apostrophes
    (for contractions).

    >>> tokens("I'm fine, how are you?")
    ["I'm", 'fine', 'how', 'are', 'you']

    """
    words = re.findall(r"\b[\w']+\b", s)
    return words