In http://docs.python.org/lib/string-methods.html, under lstrip(), it 
says,

"chars must be a string; the characters in the string will be stripped 
from the beginning of the string this method is called on".

It would be clearer if it said:

"chars must be a string; the characters in the string constitute a set 
of characters to be stripped from the beginning of the string this 
method is called on".

Similarly for rstrip() and strip().

There was a recent posting to comp.lang.python where it appears 
that the poster thought the argument to lstrip() was a leading string 
to be removed, not a set of characters.

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I notice bug #1196824 (recently submitted and closed as "not a bug") 
relates to the same issue.  It seems more than one person has gotten 
confused by this :-)

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Over the years, several people have tripped over this and posted 
to c.l.p., so I think the existing text is unclear enough to arguably 
qualify as a buglet.  In response to the same posting, I had the 
same thought of clarifying that the 'string' defines a set, so I 
support this suggestion or something similar ;-) and thank you for 
submitting it.

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It would also be helpful to note the definition of
"whitespace" in each of the strip() methods.  It appears to
be defined in strip() as being identical to
string.whitespace.  However, I do not see a built-in
whitespace for strings.

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Okay, fixed.
Thanks for the report.