Explicitly print diff stats to sys.stdout, if possible.

Explicitly print diff stats to sys.stdout, if possible.

This makes it possible to effectively re-route the stdout by
re-assigning sys.stdout.

BUG=

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=273595

[Dirk Pranke, 2014-05-29 20:31:35]

https://codereview.chromium.org/303223005/diff/1/git_cl.py
File git_cl.py (right):

https://codereview.chromium.org/303223005/diff/1/git_cl.py#newcode263
git_cl.py:263: stdout = sys.stdout.fileno()
drive-by nit: sys.stdout works fine, you don't need the fileno() ...

[szager1, 2014-05-29 20:48:04]

https://codereview.chromium.org/303223005/diff/1/git_cl.py
File git_cl.py (right):

https://codereview.chromium.org/303223005/diff/1/git_cl.py#newcode263
git_cl.py:263: stdout = sys.stdout.fileno()
On 2014/05/29 20:31:36, Dirk Pranke wrote:
> drive-by nit: sys.stdout works fine, you don't need the fileno() ...

There is some existing code that replaces sys.stdout with a StringIO, and that
won't work, because there's no file descriptor associated with a StringIO.  So,
to do what you say, I'd have to:

try:
  sys.stdout.fileno()
  stdout = sys.stdout
except AttributeError:
  stdout = None

... which seems silly to me.

[Michael Moss, 2014-05-29 20:49:11]

lgtm

[M-A Ruel, 2014-05-29 20:49:44]

Where would sys.stdout be redirected?

[szager1, 2014-05-29 20:56:52]

On 2014/05/29 20:49:44, M-A Ruel wrote:
> Where would sys.stdout be redirected?

It's for test code; I'm using this to wrap main() in git_cl:

  import git_cl

  def capture_terminal(f, *args, **kwargs):
    old_std = (sys.stdout, sys.stderr)
    bufs = (StringIO(), StringIO())
    pipes = (os.pipe(), os.pipe())
    def _thread_main(fd, buf):
      with os.fdopen(fd) as fh:
        buf.write(fh.read())
    threads = (
        threading.Thread(target=_thread_main, args=(pipes[0][0], bufs[0])),
        threading.Thread(target=_thread_main, args=(pipes[1][0], bufs[1])))
    threads[0].start()
    threads[1].start()
    sys.stdout = os.fdopen(pipes[0][1], 'w')
    sys.stderr = os.fdopen(pipes[1][1], 'w')
    try:
      result = f(*args, **kwargs)
    except Exception as e:
      sys.excepthook(*sys.exc_info())
      result = e
    sys.stdout.close()
    sys.stderr.close()
    threads[0].join()
    threads[1].join()
    (sys.stdout, sys.stderr) = old_std
    return result, bufs[0], bufs[1]

  args = [...]
  capture_terminal(git_cl.main, args)


The nice thing about this is that I can debug a test failure in pdb, without
having to deal with a subprocess call to git-cl.

[szager1, 2014-05-29 21:06:28]

The CQ bit was checked by szager@chromium.org

[commit-bot: I haz the power, 2014-05-29 21:07:45]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/szager@chromium.org/303223005/1

[commit-bot: I haz the power, 2014-05-29 21:09:37]

Change committed as 273595

[Dirk Pranke, 2014-05-29 21:10:47]

https://codereview.chromium.org/303223005/diff/1/git_cl.py
File git_cl.py (right):

https://codereview.chromium.org/303223005/diff/1/git_cl.py#newcode263
git_cl.py:263: stdout = sys.stdout.fileno()
On 2014/05/29 20:48:04, szager1 wrote:
> On 2014/05/29 20:31:36, Dirk Pranke wrote:
> > drive-by nit: sys.stdout works fine, you don't need the fileno() ...
> 
> There is some existing code that replaces sys.stdout with a StringIO, and that
> won't work, because there's no file descriptor associated with a StringIO. 
So,
> to do what you say, I'd have to:
> 
> try:
>   sys.stdout.fileno()
>   stdout = sys.stdout
> except AttributeError:
>   stdout = None
> 
> ... which seems silly to me.

You lost me, or maybe I'm not understanding something. subprocess2.call() should
be just fine w/ receiving a file-like object for the stdout= keyword parameter,
and so passing a StringIO should be fine as well.

[szager1, 2014-05-29 21:27:15]

On 2014/05/29 21:10:47, Dirk Pranke wrote:
> https://codereview.chromium.org/303223005/diff/1/git_cl.py
> File git_cl.py (right):
> 
> https://codereview.chromium.org/303223005/diff/1/git_cl.py#newcode263
> git_cl.py:263: stdout = sys.stdout.fileno()
> On 2014/05/29 20:48:04, szager1 wrote:
> > On 2014/05/29 20:31:36, Dirk Pranke wrote:
> > > drive-by nit: sys.stdout works fine, you don't need the fileno() ...
> > 
> > There is some existing code that replaces sys.stdout with a StringIO, and
that
> > won't work, because there's no file descriptor associated with a StringIO. 
> So,
> > to do what you say, I'd have to:
> > 
> > try:
> >   sys.stdout.fileno()
> >   stdout = sys.stdout
> > except AttributeError:
> >   stdout = None
> > 
> > ... which seems silly to me.
> 
> You lost me, or maybe I'm not understanding something. subprocess2.call()
should
> be just fine w/ receiving a file-like object for the stdout= keyword
parameter,
> and so passing a StringIO should be fine as well.

'File-like' in this context means 'associated with a file descriptor that can be
inherited by the subprocess.'  But why explain with words when I can explain
with code:

$ python
Python 2.7.3 (default, Feb 27 2014, 19:58:35) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cStringIO, subprocess2
>>> subprocess2.call(['ls'], stdout=cStringIO.StringIO())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "subprocess2.py", line 467, in call
    return communicate(args, **kwargs)[1]
  File "subprocess2.py", line 449, in communicate
    proc = Popen(args, **kwargs)
  File "subprocess2.py", line 237, in __init__
    super(Popen, self).__init__(args, **kwargs)
  File "/usr/lib/python2.7/subprocess.py", line 672, in __init__
    errread, errwrite) = self._get_handles(stdin, stdout, stderr)
  File "/usr/lib/python2.7/subprocess.py", line 1053, in _get_handles
    c2pwrite = stdout.fileno()
AttributeError: 'cStringIO.StringO' object has no attribute 'fileno'

[Dirk Pranke, 2014-05-29 21:32:45]

Hm. I guess I'm wrong :). Sorry! I could've sworn I've seen this work before.