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My understanding of the augmented assignment 
statements is that they should always assign to the 
variable that they read from. However, consider the 
following Python session:
 >>> class A: x = 1 
 ... 
 >>> a=A()
 >>> a.x += 1
 >>> a.x, A.x
 (2, 1)
Here, the expression "a.x += 1" read from a class 
variable, and wrote to an instance variable. A 
similar effect can occur within a member function:
 >>> class A:
 ... x = 1
 ... def f(s): s.x += 1
 ... 
 >>> a = A()
 >>> a.f()
 >>> a.x, A.x
 (2, 1)
I have elicited this behavior in Python 2.0 and 2.1 
under Linux (Redhat 6.0), and Python 2.0 on sunos5.

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Sorry, but your understanding is flawed. Changed the 
category to Documentation and assigned to Fred, because I 
agree the Ref Man isn't clear enough here: "The target is 
evaluated only once" is certainly how Guido *thinks* of it, 
but it really needs a by-cases explanation:
For an attributeref target, the primary expression in the 
reference is evaluated only once, but a getattr is done on 
the RHS and a setattr on the LHS. That is,
 e1.attr op= e2
acts like
 temp1 = e1
 temp2 = e2
 temp1.attr = temp1.attr op temp2
Etc. It's going to take some real work to write this up so 
they're comprehensible! I recommend skipping most words 
and presenting "workalike" pseudo-code sequences instead. 
That will take some sessions with the disassembler to be 
sure the pseudo-code is 100% accurate.

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IMHO, this is not a bug. Assignments are always made to the 
class instance, not the class type. X+=1 should be 
equivalent to going X=X+1, and is just so in the above 
cases.

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See attached documentation patch.

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Thanks! Check in as patched. Does the tutorial need
changes as well?

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Committed as ref6.tex 1.55 and 1.47.4.2.
Closing bug.