[Python-ideas] PEP 572: Statement-Local Name Bindings, take three!

[Ethan Furman]

On 03/24/2018 09:27 AM, Rob Cliffe via Python-ideas wrote:
> On 24/03/2018 14:44, Steven D'Aprano wrote:
>> On Sat, Mar 24, 2018 at 07:12:49PM +1000, Nick Coghlan wrote:

>>> For PEP 572, the most directly comparable example is code like this:
>>>
>>>      # Any previous binding of "m" is lost completely on the next line
>>>      m = re.match(...)
>>>      if m:
>>>          print(m.groups(0))
>>>
>>> In order to re-use that snippet, you need to double-check the surrounding
>>> code and make sure that you're not overwriting an "m" variable already used
>>> somewhere else in the current scope.
 >>
>> Yes. So what? I'm going to be doing that regardless of whether the
>> interpreter places this use of m in its own scope or not. The scope as
>> seen by the interpreter is not important.
 >
> Good for you.  But the proposed scoping rules are an extra safeguard for programmers who are less conscientious than
> you, or for anyone (including you) who is short of time, or misses something.  An extra level of protection against
> introducing a bug is IMO a Good Thing.

But it's not a free thing.  Our cars have seat belts, not six-point restraints, and either way the best practice is to 
be aware of one's surroundings, not rely on the safeguards to protect us against carelessness.


>> To the extent that this proposal to add sub-function scoping encourages
>> people to do copy-paste coding without even renaming variables to
>> something appropriate for the function they're pasted into, I think this
>> will strongly hurts readability in the long run.
 >
> I think it will aid readability, precisely for the reason Nick gives: you need to make fewer checks whether variables
> are or are not used elsewhere.

Extra levels of intermingled scope are extra complication (for humans, too!); extra complication does not (usually) help 
readability -- I agree with D'Aprano that this is not a helpful complication.

--
~Ethan~