Using msvcrt (in Windows), how to catch Enter key?

[Dick Moores]

Windows XP Pro, Python 2.5.1

import msvcrt
while True:
if msvcrt.kbhit():
key = msvcrt.getch()
if key == 'Enter'
do something

Is there a way to catch the pressing of the 'Enter' key?

Thanks,

Dick Moores

[Filip Wasilewski]

On Oct 29, 11:26 am, Dick Moores <[e-mail]:

Windows XP Pro, Python 2.5.1

import msvcrt
while True:
if msvcrt.kbhit():
key = msvcrt.getch()
if key == 'Enter'
do something

Is there a way to catch the pressing of the 'Enter' key?

Yes there is. Just open the Python shell and see what is being
returned by `getch` or `getche` functions when you press Enter:

>>import msvcrt
msvcrt.getch()

'\r'

Also try to avoid `busy waiting` and calling msvcrt.kbhit in a loop
without a sleep statement. I don't know your case but probably this
should be enough:

while True:
if msvcrt.getch() == '\r':
...

fw

[Dustan]

On Oct 29, 4:26 am, Dick Moores <[e-mail]:

Windows XP Pro, Python 2.5.1

import msvcrt
while True:
if msvcrt.kbhit():
key = msvcrt.getch()
if key == 'Enter'
do something

Is there a way to catch the pressing of the 'Enter' key?

Thanks,

Dick Moores

Let's find out:

>>from msvcrt import getch
while True:

.... key = getch()
.... if key: print repr(key)+',',
....
'p', 'r', 'e', 's', 's', 'i', 'n', 'g', ' ', 'e', 'n', 't', 'e', 'r',
':', ' ', '\r',

Gee, I pressed enter, and it returned '\r'. I wonder...

>>import msvcrt
while True:

.... if msvcrt.kbhit():
.... key = msvcrt.getch()
.... if key == '\r':
.... print "success!"
....
success!

[Dick Moores]

At 04:29 AM 10/29/2007, Filip Wasilewski wrote:

>On Oct 29, 11:26 am, Dick Moores <[e-mail]:

Windows XP Pro, Python 2.5.1

import msvcrt
while True:
if msvcrt.kbhit():
key = msvcrt.getch()
if key == 'Enter'
do something

Is there a way to catch the pressing of the 'Enter' key?

Yes there is. Just open the Python shell and see what is being
returned by `getch` or `getche` functions when you press Enter:

>import msvcrt
msvcrt.getch()

'\r'

Terrific! Thanks.

>Also try to avoid `busy waiting` and calling msvcrt.kbhit in a loop
without a sleep statement.
I don't know your case but probably this
should be enough:

while True:
if msvcrt.getch() == '\r':

I tried it and find that without the msvcrt.kbhit the first key I hit
doesn't do anything. I have to hit that key again, or another key.

Dick

[Gabriel Genellina]

On 29 oct, 09:23, Dick Moores <[e-mail]:

while True:
if msvcrt.getch() == '\r':

I tried it and find that without the msvcrt.kbhit the first key I hit
doesn't do anything. I have to hit that key again, or another key.

I'd say there is a logic error in your program then; keys don't "do
anything" by themselves.
Try posting a small sample, telling what you get and what you expect.

--
Gabriel Genellina

[Dick Moores]

At 09:26 AM 10/29/2007, Gabriel Genellina wrote:

>On 29 oct, 09:23, Dick Moores <[e-mail]:

>while True:
if msvcrt.getch() == '\r':

I tried it and find that without the msvcrt.kbhit the first key I hit
doesn't do anything. I have to hit that key again, or another key.

I'd say there is a logic error in your program then; keys don't "do
anything" by themselves.
Try posting a small sample, telling what you get and what you expect.

Huh. Works now.

import msvcrt
while True:
key = msvcrt.getch()
if key == 'h':
print 'Hello'
if key == 'b':
print 'Bye'
if key == '\r': # 'Enter' key
break

Dick

[Dick Moores]

At 09:53 AM 10/29/2007, Dick Moores wrote:

>At 09:26 AM 10/29/2007, Gabriel Genellina wrote:

On 29 oct, 09:23, Dick Moores <[e-mail]:

while True:
if msvcrt.getch() == '\r':
>
I tried it and find that without the msvcrt.kbhit the first key I hit
doesn't do anything. I have to hit that key again, or another key.

I'd say there is a logic error in your program then; keys don't "do
anything" by themselves.
Try posting a small sample, telling what you get and what you expect.

Huh. Works now.

import msvcrt
while True:
key = msvcrt.getch()
if key == 'h':
print 'Hello'
if key == 'b':
print 'Bye'
if key == '\r': # 'Enter' key
break

Dick

But here's a case where it seems I do need the

if msvcrt.kbhit() line

=========================
#!/usr/bin/env python
#coding=utf-8
import time
import msvcrt
timeNow = time.time()
oldTimeNow = timeNow
while True:
if msvcrt.kbhit():
key = msvcrt.getch()
if key == 'h':
print 'Hello'
if key == 'b':
print 'Bye'
if key == '\r': # Enter key
break
timeNow = time.time()
if timeNow - oldTimeNow 5:
print "5 seconds passed"
oldTimeNow = timeNow
==========================

Without that line:
==========================
#!/usr/bin/env python
#coding=utf-8
import time
import msvcrt
timeNow = time.time()
oldTimeNow = timeNow
while True:
#if msvcrt.kbhit():
key = msvcrt.getch()
if key == 'h':
print 'Hello'
if key == 'b':
print 'Bye'
if key == '\r': # Enter key
break
timeNow = time.time()
if timeNow - oldTimeNow 5:
print "5 seconds passed"
oldTimeNow = timeNow
============================

Without that line the "5 seconds passed" report is printed ONLY after
a "b" or an "h", not what I want.

Dick

[Gabriel Genellina]

En Mon, 29 Oct 2007 14:39:49 -0300, Dick Moores <rd*@rcblue.comescribió:

But here's a case where it seems I do need the

if msvcrt.kbhit() line

At least add a small sleep() call inside the loop, to be nice to other
running processes:

=========================
#!/usr/bin/env python
#coding=utf-8
import time
import msvcrt
timeNow = time.time()
oldTimeNow = timeNow
while True:
if msvcrt.kbhit():
key = msvcrt.getch()
if key == 'h':
print 'Hello'
if key == 'b':
print 'Bye'
if key == '\r': # Enter key
break

else:
time.sleep(0.1)

timeNow = time.time()
if timeNow - oldTimeNow 5:
print "5 seconds passed"
oldTimeNow = timeNow
==========================

--
Gabriel Genellina

[Dick Moores]

At 03:23 PM 10/29/2007, Gabriel Genellina wrote:

>En Mon, 29 Oct 2007 14:39:49 -0300, Dick Moores <rd*@rcblue.comescribió:

But here's a case where it seems I do need the

if msvcrt.kbhit() line

At least add a small sleep() call inside the loop, to be nice to other
running processes:

=========================
#!/usr/bin/env python
#coding=utf-8
import time
import msvcrt
timeNow = time.time()
oldTimeNow = timeNow
while True:
if msvcrt.kbhit():
key = msvcrt.getch()
if key == 'h':
print 'Hello'
if key == 'b':
print 'Bye'
if key == '\r': # Enter key
break

else:
time.sleep(0.1)

timeNow = time.time()
if timeNow - oldTimeNow 5:
print "5 seconds passed"
oldTimeNow = timeNow
=========================

Yes, that makes a major difference in the CPU
usage percentage on my computer. In fact I can't
even tell that there is anything going on other
than the usual behind-the-scenes XP stuff. CPU
usage stays right around 0% or 6%, with an
occasional 6% and a very occasional 15%.
Interestingly, sleep(0.001) makes as big a
difference as your sleep(0.1), but sleep(0.0001) bumps it up to a steady100%!

Thanks,

Dick

[Gabriel Genellina]

En Mon, 29 Oct 2007 21:22:36 -0300, Dick Moores <rd*@rcblue.comescribió:

At 03:23 PM 10/29/2007, Gabriel Genellina wrote:

>En Mon, 29 Oct 2007 14:39:49 -0300, Dick Moores <rd*@rcblue.com>
escribió:
At least add a small sleep() call inside the loop, to be nice to other
running processes:

Yes, that makes a major difference in the CPU
usage percentage on my computer. In fact I can't
even tell that there is anything going on other
than the usual behind-the-scenes XP stuff. CPU
usage stays right around 0% or 6%, with an
occasional 6% and a very occasional 15%.
Interestingly, sleep(0.001) makes as big a
difference as your sleep(0.1), but sleep(0.0001) bumps it up to a steady
100%!

The underlying function in Windows is Sleep (or SleepEx) which takes an
argument in milliseconds. 0.0001s = 0.1ms and it's rounded to 0. Sleep(0)
has very specific semantics - for a single threaded program, it does
nothing, so your code is effectively a busy loop taking 100% CPU.

--
Gabriel Genellina

[Dick Moores]

At 06:34 PM 10/29/2007, Gabriel Genellina wrote:

>En Mon, 29 Oct 2007 21:22:36 -0300, Dick Moores <rd*@rcblue.comescribió:

At 03:23 PM 10/29/2007, Gabriel Genellina wrote:

En Mon, 29 Oct 2007 14:39:49 -0300, Dick Moores <rd*@rcblue.com>
escribió:
At least add a small sleep() call inside the loop, to be nice to other
running processes:

Yes, that makes a major difference in the CPU
usage percentage on my computer. In fact I can't
even tell that there is anything going on other
than the usual behind-the-scenes XP stuff. CPU
usage stays right around 0% or 6%, with an
occasional 6% and a very occasional 15%.
Interestingly, sleep(0.001) makes as big a
difference as your sleep(0.1), but sleep(0.0001) bumps it up to a steady
100%!

The underlying function in Windows is Sleep (or SleepEx) which takes an
argument in milliseconds. 0.0001s = 0.1ms and it's rounded to 0. Sleep(0)
has very specific semantics - for a single threaded program, it does
nothing, so your code is effectively a busy loop taking 100% CPU.

Ah, useful information. Thank you. Where'd you learn that?

Dick Moores

[Gabriel Genellina]

En Tue, 30 Oct 2007 01:46:19 -0300, Dick Moores <rd*@rcblue.comescribió:

At 06:34 PM 10/29/2007, Gabriel Genellina wrote:

>The underlying function in Windows is Sleep (or SleepEx) which takes an
argument in milliseconds. 0.0001s = 0.1ms and it's rounded to 0.

Ah, useful information. Thank you. Where'd you learn that?

Microsoft's Windows API Reference:
http://msdn2.microsoft.com/en-us/library/aa383749.aspx

The Sleep function is at
http://msdn2.microsoft.com/en-us/library/ms686298.aspx

--
Gabriel Genellina