[Python-Dev] arguments policy: **kwargs.pop()

[Christian Tismer]

Hi guys,

I tried to find advice for hours, but failed so fer, so here is my question:

Whenever I think to adopt a new module that does a good job, I always
can't stand the temptation to look at the coding style and certain
principles.

Then I rather often see things like this:

class someclass(object):
    # note that there is no comment about argument destruction...

    def __init__(self, **kwargs):
        first_arg = kwargs.pop('option_1', somedefault)
        ...
        nth_arg = kwargs.pop('option_n', somedefault')
        ...

That is:
There are arguments "consumed" rigorously by the __init__ of a class,
although it would be equivalent to use kwargs.get(..., ...).

Happened to me again, today and blocked me completely, since I don't
know if I saw bad programming style or if I'm mislead.

I agree there are valid cases when if makes sense to filter out some
arguments
that a subsequently called super() might not be able to handle.
Bu even then, I would probably have a copy and make the filtering more
explicit.

But most of the time, there is no reason for using this pattern, and there
is also no comment stating that the argument dict is modified by the callee
for no good reason.

I always used the policy that arguments are never changed by a function,
unless explicitly stated.
But since I see this pattern quite frequently, I wanted to ask if I am
right by
thinking this way, or if the general policy is more like "arguments may be
destroyed by default".

What do you think? Is this bad style and should be noticed somewhere,
or is the caller supposed to protect the arguments, or are my worries
useless?

Thanks & cheers -- Chris

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