Exercise 3 solution

    import re

    q = re.compile(r"'([^']*)'|\"([^\"]*)\"|(\S+)")
    s = """say 'hello world' to "big wide" world"""

    words = [next(g for g in m.groups() if g is not None) for m in q.finditer(s)]
    print(words)
    # ['say', 'hello world', 'to', 'big wide', 'world']

(All lines were run and printed exactly what is shown.)

Explanation: the pattern has three alternatives with one group each: single
quoted text, double quoted text, and a bare word. Only the group of the
alternative that matched is not None, so next(...) picks it out. Quoted
alternatives come before \S+ so that a quote mark starts a phrase instead of
a plain word. Note that a quoted empty string ('') would give '' which is not
None, so it is still kept correctly; that is why the test is "is not None"
and not simply "truthy".