[issue21364] Documentation Recommends Broken Pattern

[Armin Ronacher]

Armin Ronacher added the comment:

> I would like to know of some situations where you want to write some
> code that accesses standard streams as binary *and* don't control the
> application setup (i.e. library code rather than application code). It
> seems to me that a library should take the binary streams as parameters
> rather than force the use of stdin/stdout.

The same situations people wrapped streams before on python 2:

* code.py users.  Werkzeug's traceback system implements a remote python 
  shell through it.
* any system that wants to unittest shell scripts on a high level.
* any system that wants to execute arbitrary python code and then
  capture whatever output it did.  This is for instance what I see
  Sphinx users frequently do (or doctests)

In fact, the reasons people wrap sys.stdout/sys.stderr on 2.x are the same reasons why people would do it on 3.x: they have arbitrary code they did not write and they want to capture what it does.

Since you do not know if that is binary or text you need a stream object that behaves the same way as the default one.

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<http://bugs.python.org/issue21364>
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