Suppose this string:
The fox jumped over the log.
Turning into:
The fastest you can get for user-generated strings is:
if ' ' in text:
while ' ' in text:
text = text.replace(' ', ' ')
The short circuiting makes it slightly faster than pythonlarry's comprehensive answer. Go for this if you're after efficiency and are strictly looking to weed out extra whitespaces of the single space variety.