Re: Best way of finding terminal width/height?

On 2006-02-07, Joel Hedlund <joel.hedlund@xxxxxxxxx> wrote:

You just call the failed read() or write() again. Unless
there's some way that the read/write partially succeeded and
you don't have any way to know how many bytes were
read/written, If that's the case then Python's "file" object
read and write would appear to be broken by design.

Wow... I tried to set up an example that would fail, and it
didn't. It seems the test only fails if I use the keyboard to
cram stuff into stdin, and not if stdin is a regular pipe.

That's what I'd expect. Resizing the terminal should have no
effect on read() calls that are pending on other things.

Could this perhaps be some kind of misbehavior on behalf of my
terminal emulator (GNOME Terminal 2.12.0 in Ubuntulinux 5.10)?

Nope. Resign the terminal will abort pending I/O operations on
that terminal. It won't terminal I/O operations pending on
other devices/files.

Then run the prog and pipe a large chunk of text into stdin, and redirect stdout to a file:

$ cat /a/large/text/file | python winch.py > copy.of.the.large.file

Now, what happens for me is exactly what I wanted. I can
resize the window as much as I like, and a diff

Sure.

$ diff /a/large/text/file copy.of.the.large.file

comes up empty. A perfectly good copy.

However, if I do this instead (try to use keyboard to push stuff into stdin):

$ python winch.py > copy.of.the.large.file

I expect python not to return until I press Ctrl-D on my
keyboard,

sys.stdin.read() will return when there's an EOF or when the
underyling read() call is aborted by a signal.

but it does return as soon as I enter more than one
line of text and then resize the window (one unterminated line
is ok).

Example text to type in:
moo moo
cow cow

As soon as I have typed in something that includes a newline
charater through the keyboard and try to resize the terminal,
sys.stdin.read() will return whatever I put in no far and no
exception raised.

Yup. That does indeed appear to be the way it works. :)

Weird. Could it in fact my terminal that's screwing things up
for me?

No.

Try this out:

----------------------------------------------------------------------
#!/usr/bin/python
import signal, os, sys

_bTerminalSizeChanged = False

def report_terminal_size_change(signum, frame):
global _bTerminalSizeChanged
_bTerminalSizeChanged = True

signal.signal(signal.SIGWINCH, report_terminal_size_change)

while True:
try:
s = sys.stdin.read()
if not s:
break
sys.stdout.write(s)
except IOError:
sys.stderr.write("IOError\n")
if _bTerminalSizeChanged:
sys.stderr.write("SIGWINCH recevied\n")
_bTerminalSizeChanged = False
----------------------------------------------------------------------

In that example, I handle IOError on write with the same
exception handler as the one for read. That may not be exactly
what you want to do, but it does demonstrate what
window-resizing does.

When the window is resized, the SIGWINCH handler will be
called. A pending read() may abort with an IOError, or it may
just return some buffered data.

--
Grant Edwards grante Yow! Send your questions
at to "ASK ZIPPY", Box 40474,
visi.com San Francisco, CA 94140,
USA
.

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