A simple way to print few line stuck to the same position

[Sarcar, Shourya C (GE Healthcare)]

A way to do this on DOS/Windows console would be:

import sys
for r in range(0,2**16):
	line = "Count : %d" % r
	sys.stdout.write(line)
	sys.stdout.flush()
	# do something that consumes time
	backup = "\b" * len(line) # The backspace character; this will
prevent characters from the prev "print" showing up	
	sys.stdout.write(backup)
	sys.stdout.flush()

Regards,
Shourya
http://partlytrue.wordpress.com/


P.S: This is my first post to the list and I am new to python and I have
Outlook as my mail client. Can't get worse. I am sure I am flouting some
response/quoting etiquette here. If someone could guide, I would be most
grateful.

-----Original Message-----
From: python-list-bounces+shourya.sarcar=med.ge.com at python.org
[mailto:python-list-bounces+shourya.sarcar=med.ge.com at python.org] On
Behalf Of Hans Mulder
Sent: Sunday, June 05, 2011 4:31 AM
To: python-list at python.org
Subject: Re: A simple way to print few line stuck to the same position

On 4/06/11 13:14:05, TheSaint wrote:
> Hans Mulder wrote:

>> A minimalist solution would be to print the labels ("This count", 
>> etc.) only once, and position the cursor after it to update the
report.

> Generally a good point. Similar sequences are working for coloring and

> formatting text.

As I said, VT100 sequences work in pretty much any modern terminal or
emulator (but not in a DOS box under Windows).

> I don't know whether the program would behave to someone else who 
> using not konsole like I do.

If you use the "\033[H" sequence to move the cursor to a predefined
postition, you'll find that other people's windows have a different size
from yours.  The standard library provides thin wrappers around the
low-level calls need to figure out the window size:

import array
import fcntl
import sys
import termios

def getwindowsize():
     buf = array.array('h', [0] * 4)
     res = fcntl.ioctl(sys.stdout, termios.TIOCGWINSZ, buf, True)
     return buf[0:2]

rows, columns = getwindowsize()

print rows, columns

Alternatively, you could parse the output of `stty -a`.

Oh, and people will resize their window while your script is running,
and expect it to respond sensibly.  You could install a handler for
SIGWINCH signals, but at this point curses will begin to look more and
more attractive, as it will handle these details for you.

But then, maybe you can avoid absolute coordinates altogether.  If your
report is always exactly six lines, you could write the sequence
"\r\033[5A" after each report.  This moves the cursor to the left margin
and five lines up, ready to overwrite the previous report, independent
of window size.

>> The module is called "curses" and, yes, it would be the best way to
go.

> OK, I didn't understand if I must setup a window first in order to 
> implement cursor positioning.

If you use curses, you must initialize it by calling curses.initscr(),
which returns a "WindowObject" representing the konsole window.  To put
things on the screen, you call methods on this object.  Keep in mind
that a "window" in curses jargon is just a rectangle inside your konsole
window.  You can't create real Windows using curses.

Whether or not you use curses, if the numbers in the current report can
be smaller than those in the previous report, you'll want to write some
spaces after each number to erase the previous number.  For example, if
you try to overwrite "this count: 10" with "this count: 9", you'll end
up with "this count: 90" on the screen.  You don't want that to happen.


Hope this helps,

-- HansM



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