I like the idea of an scans like ability, but I"m afraid the existing
format language is poorly suited to that.
It's simply no designed to be a two-way street:
* ANYTHING can be stringified in Python -- so there is no defined way to
turn a string back into a particular type.
OK, so we restrict ourselves to builtins -- how would you reverse this:
In [17]: x, y, z = 23, 45, 67
In [18]: f"{x}{y}{z}"
Out[18]: '234567'
so we require a type specifier, but similar problem:
In [19]: f"{x:d}{y:d}{z:d}"
Out[19]: '234567'
So we require a field size specifier:
In [20]: f"{x:2d}{y:2d}{z:2d}"
Out[20]: '234567'
OK, I guess that is clearly defined. but we've now limited ourselves to a
very small subset of the formatting language -- maybe it's not the right
language for the job?
-CHB
On Thu, Sep 17, 2020 at 1:08 PM Alex Hall <[email protected]> wrote:
> On Thu, Sep 17, 2020 at 9:50 PM Ricky Teachey <[email protected]> wrote:
>
>> On Thu, Sep 17, 2020 at 3:44 PM Alex Hall <[email protected]> wrote:
>>
>>>
>>> On Thu, Sep 17, 2020 at 9:27 PM Ricky Teachey <[email protected]> wrote:
>>>
>>>> A difficulty I have with the idea as presented is this.
>>>>
>>>> If I can say this:
>>>>
>>>> "{x:d} {y:d} {z:d}" = "1 2 3"
>>>>
>>>> ...thus assigning 1, 2, 3 to x, y, z respectively, I might want to also
>>>> do the same thing this way:
>>>>
>>>> q = "{x:d} {y:d} {z:d}"
>>>> q = "1 2 3"
>>>>
>>>> The intent being: save the f-string as a variable, and then use it to
>>>> assign later. But that can obviously never work because q would just become
>>>> the string "1 2 3" .
>>>>
>>>
>>> The same problem exists for assignments to tuples, subscripts,
>>> attributes, even plain variables. I've often wanted to put an assignment
>>> target in a variable.
>>>
>>
>> Feels to me akin to what Einstein called spooky action at a distance. ;)
>>
>> # module A
>> x = f"{a:d}"
>>
>> # module B
>> x.parse("1")
>> assert a == 1
>>
>> This seems like a joke I would want to play on someone*, not a useful
>> feature.
>>
>> * well, if i were a bad person... ;)
>>
>>
> I'm not actually proposing being able to store assignment targets in
> variables. I'm saying the hypothetical misconception you bring up already
> exists for every other kind of thing that can be assigned to, because they
> all intentionally look like expressions. I don't think I've ever seen
> learners be confused about this. I don't think it's a good argument against
> the proposal.
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--
Christopher Barker, PhD
Python Language Consulting
- Teaching
- Scientific Software Development
- Desktop GUI and Web Development
- wxPython, numpy, scipy, Cython
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