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Groups > comp.lang.python > #92455

Re: enhancement request: make py3 read/write py2 pickle format

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Snipped aplenty.

On Wed, Jun 10, 2015 at 8:21 PM, Steven D'Aprano <steve@pearwood.info> wrote:
> On Thu, 11 Jun 2015 08:10 am, Devin Jeanpierre wrote:
> [...]
>> I could spend a bunch of time writing yet another config file format,
>> or I could use text format protocol buffers, YAML, or TOML and call it
>> a day.
>
> Writing a rc parser is so trivial that it's almost easier to just write it
> than it is to look up the APIs for YAML or JSON, to say nothing of the
> rigmarole of defining a protocol buffer config file, compiling it,
> importing the module, and using that.
>
-snip
>
> That's a basic, *but acceptable*, rc parser written in literally under a
> minute. At the risk of ending up with egg on my face, I reckon that it's so
> simple and so obviously correct that I can tell it works correctly without
> even testing it. (Famous last words, huh?)

I won't try to egg you. That said, you have to write tests. Also,
everyone who uses it has to learn the format and API, and it may have
corner cases you aren't aware of, it has to get ported to python 3 if
you wrote it for python 2, the parsing errors are obscure and might
need improvement, and so on. There's a place for this, but I suspect
it is small compared to the place where it seemed like a good idea at
the time.

>>> Beyond simple needs, like rc files, literal_eval is not sufficient. You
>>> can't use it to deserialise arbitrary objects. That might be a feature,
>>> but if you need something more powerful than basic ints, floats, strings
>>> and a few others, literal_eval will not be powerful enough.
>>
>> No, it is powerful enough. After all, JSON has the same limitations.
>
> In the sense that you can build arbitrary objects from a combination of a
> few basic types, yes, literal_eval is "powerful enough" if you are prepared
> to re-invent JSON, YAML, or protocol buffer.
>
> But I'm not talking about re-inventing what already exists. If I want JSON,
> I'll use JSON, not spend weeks or months re-writing it from scratch. I
> can't do this:
>
> class MyClass:
>     pass
>
> a = MyClass()
> serialised = repr(a)
> b = ast.literal_eval(serialised)
> assert a == b

I don't understand. You can't do that in JSON, YAML, XML, or protocol
buffers, either. They only provide a small set of types, comparable to
(but smaller) than the set of types you get from literal_eval/repr.

-- Devin

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Re: enhancement request: make py3 read/write py2 pickle format Chris Angelico <rosuav@gmail.com> - 2015-06-10 09:06 +1000
  Re: enhancement request: make py3 read/write py2 pickle format Irmen de Jong <irmen.NOSPAM@xs4all.nl> - 2015-06-10 02:17 +0200
    Re: enhancement request: make py3 read/write py2 pickle format Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-09 17:47 -0700
      Re: enhancement request: make py3 read/write py2 pickle format Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-10 13:52 +1000
        Re: enhancement request: make py3 read/write py2 pickle format random832@fastmail.us - 2015-06-09 23:57 -0400
          Re: enhancement request: make py3 read/write py2 pickle format Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-10 15:43 +1000
        Re: enhancement request: make py3 read/write py2 pickle format Chris Angelico <rosuav@gmail.com> - 2015-06-10 14:00 +1000
        Re: enhancement request: make py3 read/write py2 pickle format Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-09 21:48 -0700
          Re: enhancement request: make py3 read/write py2 pickle format Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-10 19:36 +1000
            Re: enhancement request: make py3 read/write py2 pickle format Irmen de Jong <irmen.NOSPAM@xs4all.nl> - 2015-06-10 19:34 +0200
            Re: enhancement request: make py3 read/write py2 pickle format Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-10 15:10 -0700
              Re: enhancement request: make py3 read/write py2 pickle format Steven D'Aprano <steve@pearwood.info> - 2015-06-11 13:21 +1000
                Re: enhancement request: make py3 read/write py2 pickle format Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-10 22:39 -0700
                Re: enhancement request: make py3 read/write py2 pickle format Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-11 19:20 +1000
            Re: enhancement request: make py3 read/write py2 pickle format Terry Reedy <tjreedy@udel.edu> - 2015-06-10 19:25 -0400
            Re: enhancement request: make py3 read/write py2 pickle format Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-10 16:39 -0700
            Re: enhancement request: make py3 read/write py2 pickle format Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-10 16:48 -0700
            Re: enhancement request: make py3 read/write py2 pickle format Terry Reedy <tjreedy@udel.edu> - 2015-06-10 19:46 -0400
            Re: enhancement request: make py3 read/write py2 pickle format Chris Angelico <rosuav@gmail.com> - 2015-06-11 09:58 +1000
            Re: enhancement request: make py3 read/write py2 pickle format Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-06-10 17:02 -0700
              Re: enhancement request: make py3 read/write py2 pickle format Marko Rauhamaa <marko@pacujo.net> - 2015-06-11 07:08 +0300
            Re: enhancement request: make py3 read/write py2 pickle format Serhiy Storchaka <storchaka@gmail.com> - 2015-06-11 14:11 +0300
    Re: enhancement request: make py3 read/write py2 pickle format Chris Angelico <rosuav@gmail.com> - 2015-06-10 11:03 +1000

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