[Python-ideas] PEP 3150 (statement local namespaces) updated based on April discussion

[geremy condra]

On Mon, Jun 13, 2011 at 1:09 PM, Terry Reedy <tjreedy at udel.edu> wrote:
> On 6/13/2011 12:59 PM, geremy condra wrote:
>>
>> On Sun, Jun 12, 2011 at 2:20 PM, Terry Reedy<tjreedy at udel.edu>  wrote:
>
>>> 'Given' or 'where' constructs are sometimes used in mathematical
>>> writings,
>>> especially formula exposition, but they typically, if not always, are
>>> isolated (like the examples in the PEP), and not part of a code sequence.
>>> So
>>> this is notreally a precedent to me. Example:
>>>
>>>  fv = p * (1 + i/12)**t... , where
>>>    fv = present value
>>>    p  = principle
>>>    i  = nominal annual interest rate
>>>    t  = time in months
>>>
>>> -(1+whatever)
>>
>> I've historically been in favor of this kind of proposal specifically
>> because I'd like to be able to write the above code,
>
> Part of my point is that the above is not *code* (and hence not an argument
> for formatting code that way). It is a text definition. Someone who wrote
> something like the above might very well then write a *code* version the
> equivalent of
>
> p = input("principle: ")
> i = input("nominal annual interest rate: ")
> t = input("time in months: ")
> print("Future value of ${} at {}% after {} months is ${}"
>      .format(p, i, t, p*(1+i/12)**t

Meh, semantics. I could, hypothetically, write the following:

y = sqrt(z**2 + x**2) given:
    z = get_adjacent_side_length()
    x = get_opposite_side_length()

and in terms of exposition style it would be basically the same as
what you put up earlier, and is (to me) more readable than:

z = get_adjacent_side_length()
x = get_opposite_side_length()
y = sqrt(z**2 + x**2)

for the same reasons. The question is whether the (admittedly
arguable) gain in readability offered in situations like this is worth
the extra complexity of implementation and the risk of seeing code
like the examples from the PEP in practice.

Also, just to make sure I'm being clear- Nick, I'm not trying to bash
your code. I just think that right now this lends itself to some
really hard-to-understand constructions.

Geremy Condra

Geremy Condra