Timeout on file write?

[Chris Farley]

I'm working on a cross-platform Python program that prints to a receipt
printer. The code is simple, I just do something like this:

printer = file('/dev/lp0','w') # on Win32, change to 'lpt1'
p.write("whatever")
p.close()


I would like to gracefully handle situations such as when the paper is out
or the printer is powered off. Right now the program just hangs.

Suggestions? Thanks...

 

[Larry Bates]

Not tested, but you might want to take a look at:

http://www.geocities.com/dinceraydin/python/indexeng.html

second option, you could try something like:
p.write("whatever")
try:
p.write("whatever")
p.flush()

except:
print "Write error on receipt printer"

p.close()

Just possible solutions, not tested.

HTH,
Larry Bates
Syscon, Inc.

 

[Chris Farley]

second option, you could try something like:
p.write("whatever")
try:
p.write("whatever")
p.flush()

except:
print "Write error on receipt printer"

p.close()

This doesn't work, as the call to flush just hangs if the printer is
powered down. It does not throw an exception.

Would it work to start a new thread, and if the thread doesn't return
in a specified time, destroy it? I've read that Python thread's can not
be interrupted, so I'm a bit skeptical that this would work...

 

[Mathias Waack]

I would like to gracefully handle situations such as when the paper
is out or the printer is powered off. Right now the program just
hangs.

The simplest way would be to use a timeout as described in the python
lib docs, have a look at the signal module.

Mathias

 

[Chris Farley]

The simplest way would be to use a timeout as described in the python
lib docs, have a look at the signal module.

Thank you, that's exactly what I needed!