binascii.b2a_base64() should not append a "courtesy
newline".  See attached patch (but the test suite
should be updated too).

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But won't this break working code?  I believe the courtesy
newline is documented. If people program around this
naively, their code will break.

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You're right, the newline is documented in b2a_base64().  I
actually hit this problem through the base64 module, which
uses binascii underneath.  The extra newline is implied in
the example, but not really documented.  I think it may also
be a bit misleading to quote RFC 1521 where that RFC does
not (I think) require the newline.

Two options:

- reassign to Fred for updating the base64 documentation
about the extra newline.

- get rid of the extra newline in base64 only, not in
binascii.  This can be accomplished by looking at the source
string: if it has a trailing newline, leave one in, if it
doesn't strip the extra newline from the result string. 
That's the solution I'll use in the email package if we
don't change base64.

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Whether or not it's documented for base64, changing that
will also break existing code.

It's a documentation issue (unfortunately).

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What in the base64 module needs to have documentation
corrected?  It sounds like the encode() and encodestring()
functions should be documented as generating a trailing
newline; is this correct?

Set status to pending.  Barry, when you respond to this
request for information the issue will be re-opened and
assigned to me.

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Correct.  base64.encode() and base64.encodestring() should
be documented as adding a trailing newline, but only if the
source string doesn't already end in a newline (i.e:

base64.encodestring('hello') == base64.encodestring('hello\n')

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Fixed in Doc/lib/libbase64.tex revision 1.19.