[Python-ideas] Statement local namespaces - a different perspective

[Mike Meyer]

Last night, I realized something interesting about statement local
namespaces:

    Pretty much all the arguments, both for and against, apply to
    allowing suites in compound statements.

I take it as given that any suite in a statement can be refactored
into a function definition and an appropriate invocation of that
function, even though it may require returning a tuple into a tuple
assignment. This is one of the key features of programming languages
in general.

So we could, in theory, restrict all compound statements suites to a
single statement. If you needed more than one statement in them, you'd
have to wrap the suite in a named function and invoke it
appropriately.

The benefits from this restriction would be the same as they are for
disallowing statement-local namespaces: it makes the suite available
for independent testing and reuse, forces the programmer to come up
with a (hopefully) descriptive name, and forces parts to be defined
before they are used. The downsides are the same problems that the
statement-local namespace proposals are addressing: having to come up
with a good name, polluting the namespace, and giving the parts more
prominent placement than the whole.

Python doesn't do this for compound statements because it's
impractical. Not every arbitrary collection of statements that needs
to be grouped in a suite has a descriptive name or needs to be
reused. Putting them in a named function just means you should test
the function as well as the statement.  In such cases, it's better to
just embed the suite into the statement, and Python allows that.

I believe the same thing applies to values in an expression. Not every
group of sub-expressions has a good name or needs to be
reused. Putting them in a named function just means you should test
the function as well as the statement. In such cases, the code would
be better if you could just embed the suite into the statement. I
think it's time Python allowed that.

  <mike
-- 
Mike Meyer <mwm at mired.org>		http://www.mired.org/
Independent Software developer/SCM consultant, email for more information.

O< ascii ribbon campaign - stop html mail - www.asciiribbon.org