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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Tue, 23 Jun 2015 13:30:46 -0600
Subject: Re: method returns object reference
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Xref: csiph.com comp.lang.python:93046

On Tue, Jun 23, 2015 at 12:32 PM, Tim <jtim.arnold@gmail.com> wrote:
> The code below prints the following two lines, showing how the 'newkey' i=
s now inside the Client response, even though it was set in the worker.  Th=
is must be bad practice!  In my real code, the response is no longer an ins=
tance variable, which fixed the problem. It never had any business being bo=
und to the client anyway.

I agree. There may be reasons why the client would want to hold onto
the response, e.g. caching, but there are none evident in the code you
posted. What it *shouldn't* do if it's going to hold on to state like
that is share it with external code without at least a contract
defining allowed mutations. If the consumer can't reasonably be
expected not to modify the shared state, then it should be copied, not
shared.