[issue13609] Add "os.get_terminal_size()" function

[Zbyszek Szmek]

Zbyszek Szmek <zbyszek at in.waw.pl> added the comment:

> New try (I fixed my email address and the patch).
>
> The purpose of os.get_terminal_size() is the same as `stty size`, so 
> `stty size` could be a model for behavior of os.get_terminal_size().
I guess that this fallback will make some things easier. As long it is documented, the user should be able to get whatever behaviour they want.

I have four small questions:
- -1 is used as the argument meaning "try stdout and stdin". But -1 is 
  also used the error return value for open(2) and other system 
  functions. I know that Python checks the return value to throw an 
  exception, and -1 shouldn't "leak" and be passed by mistake to 
  os.get_terminal_size(). Can someone confirm that this is
  the case?
- Why stderr is not checked too? It would make os.get_terminal_size()
  return the real terminal value in a the middle of a pipe:
    cat | python -c 'import os; os.get_terminal_size()' | cat.
- some doc change is missing
- in the new version the line with ioctl(fd, TIOCGWINSZ, &w) repeats
  three times. It think it could be reduced to two without loss
  of readability.

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<http://bugs.python.org/issue13609>
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