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Sat Jun 26 17:50:27 EDT 2004 · https://mail.python.org/pipermail/python-dev/2004-June/045651.html

On Jun 26, 2004, at 10:27 AM, Phillip J. Eby wrote:

> Actually, he very well might, and a number of other people definitely 
> do.  One use case repeatedly mentioned on Python-Dev has been to 
> register functions or classes with frameworks, therefore definitely 
> involving a literal side-effect (i.e. modification to an unrelated 
> data structure).

IMHO, the fact that this results in a modification to a data structure 
in framework code is an implementation detail;  conceptually it can be 
argued that this is *still not a side-effect* --- you are in essence 
*saying something about* the function or object in question, not 
expressing something algorithmic.  My fear is that we end up seeing 
stuff like this:

[SomeDecorator(someFreeVariable=Assignment)]
def foo(...):
     x = someFreeVariable
    ...

My biggest concern in all this is that we end up muddying up 
readability and clarity by trying to improve it.

> (I wonder if I should submit a patch for PEP 318 to add this to the 
> motivation section, because it seems a lot of people keep repeating 
> this "no side-effects metadata" misconception.)

I think that before we "clarify" the PEP that the intent here *is* to 
allow side-effects we should get some clarity on what a side-effect 
*is.*  Clearly there's enough lack of consensus about this;  perhaps we 
need to see more examples of how various folks would use it.

jb

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[Python-Dev] Re: decorators and 2.4