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Re: Returning a custom file object (Python 3)

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On 28 May 2015 at 03:16, Steven D'Aprano <steve@pearwood.info> wrote:
> I'd like to return a custom file object, say my own subclass. I can easily
> subclass the file object:
>
>
> from io import TextIOWrapper
> class MyFile(TextIOWrapper):
>     pass
>
>
> but how do I tell open() to use MyFile?

Does the below do what you want?

#!/usr/bin/env python3

class Wrapper:
    def __init__(self, wrapped):
        self._wrapped = wrapped
    def __getattr__(self, attrname):
        return getattr(self._wrapped, attrname)
    # Special methods are not resolved by __getattr__
    def __iter__(self):
        return self._wrapped.__iter__()
    def __enter__(self):
        return self._wrapped.__enter__()
    def __exit__(self, *args):
        return self._wrapped.__exit__(*args)

class WrapFile(Wrapper):
    def write(self):
        return "Writing..."

f = WrapFile(open('wrap.py'))
print(f.readline())
with f:
    print(len(list(f)))
print(f.write())

>
> Answers for Python 3, thanks.

Tested on 3.2.


--
Oscar

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Thread

Returning a custom file object (Python 3) Steven D'Aprano <steve@pearwood.info> - 2015-05-28 12:16 +1000
  Re: Returning a custom file object (Python 3) Ben Finney <ben+python@benfinney.id.au> - 2015-05-28 12:40 +1000
    Re: Returning a custom file object (Python 3) Marko Rauhamaa <marko@pacujo.net> - 2015-05-28 08:29 +0300
      Re: Returning a custom file object (Python 3) Chris Angelico <rosuav@gmail.com> - 2015-05-28 15:49 +1000
        Re: Returning a custom file object (Python 3) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-28 17:04 +1000
          Re: Returning a custom file object (Python 3) Chris Angelico <rosuav@gmail.com> - 2015-05-28 19:06 +1000
      Re: Returning a custom file object (Python 3) Gary Herron <gherron@digipen.edu> - 2015-05-27 22:56 -0700
        Re: Returning a custom file object (Python 3) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-28 16:52 +1000
  Re: Returning a custom file object (Python 3) Ben Finney <ben+python@benfinney.id.au> - 2015-05-28 12:34 +1000
  Re: Returning a custom file object (Python 3) Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-05-28 10:29 +0100

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