Thank you guys for seeing my post.
First, the following is my code:
import os
print("You can create your own message for alarm.")
user_message = input(">> ")
print("\n<< Sample alarm sound >>")
for time in range(0, 3):
os.system('say ' + user_message) # this code makes sound.
print("\nOkay, The alarm has been set.")
"""
##### My problem is here #####
##### THIS IS NOT STOPPED #####
while True:
try:
os.system('say ' + user_message)
except KeyboardInterrupt:
print("Alarm stopped")
exit(0)
"""
My problem is that Ctrl + C does not work!
I tried changing position of try block, and making signal(SIGINT) catching function.
But those also does not work.
I have seen https://stackoverflow.com/a/8335212/5247212, https://stackoverflow.com/a/32923070/5247212, and other several answers about this problem.
I am using MAC OS(10.12.3) and python 3.5.2.
This is expected behaviour, as os.system() is a thin wrapper around the C function system(). As noted in the man page, the parent process ignores SIGINT during the execution of the command. In order to exit the loop, you have to manually check the exit code of the child process (this is also mentioned in the man page):
import os
import signal
while True:
code = os.system('sleep 1000')
if code == signal.SIGINT:
print('Awakened')
break
However, the preferred (and more pythonic) way to achieve the same result is to use the subprocess module:
import subprocess
while True:
try:
subprocess.run(('sleep', '1000'))
except KeyboardInterrupt:
print('Awakened')
break
Your code would then look like something like this:
import subprocess
print("You can create your own message for alarm.")
user_message = input(">> ")
print("\n<< Sample alarm sound >>")
for time in range(0, 3):
subprocess.run(['say', user_message]) # this code makes sound.
print("\nOkay, The alarm has been set.")
while True:
try:
subprocess.run(['say', user_message])
except KeyBoardInterrupt:
print("Alarm terminated")
exit(0)
As an added note, subprocess.run() is only available in Python 3.5+. You can use subprocess.call() to achieve the same effect in older versions of Python.
Also catch "SystemExit"
except (KeyboardInterrupt, SystemExit):
print("Alarm stopped")
The problem seems to be that Ctrl+C is captured by the subprocess you call via os.system. This subprocess reacts correspondingly, probably by terminating whatever it is doing. If so, the return value of os.system() will be not zero. You can use that to break the while loop.
Here's an example that works with me (substituting say by sleep):
import os
import sys
while True:
try:
if os.system('sleep 1 '):
raise KeyboardInterrupt
except KeyboardInterrupt:
print("Alarm stopped")
sys.exit(0)
If Ctrl-C is captured by the subprocess, which is the case here, the simplest solution is to check the return value of os.system(). For example in my case it returns value of 2 if Ctrl-C stops it, which is a SIGINT code.
import os
while True:
r = os.system(my_job)
if r == 2:
print('Stopped')
break
elif r != 0:
print('Some other error', r)
Related
I have a python script (xyz.py) that I run through the command prompt. My question is that don't we have any method which helps to resume the python code automatically from where it was lost the VPN connection, without any manual intervention. This will help to avoid monitoring the code frequently. Below is my code but it reads from the start if there is any disconnection. Please suggest.
filename = 'xyz.py'
while True:
p = subprocess.Popen('python '+filename, shell=True).wait()
""" #if your there is an error from running 'xyz.py',
the while loop will be repeated,
otherwise the program will break from the loop"""
if p != 0:
continue
else:
break
If me, time.sleep will be used:
import os
import time
from datetime import datetime
import requests
script = 'xyz.py'
def main():
network_check_url = 'http://8.8.8.8'
while True:
try:
requests.get(network_check_url)
except Exception as e:
print(datetime.now(), e)
time.sleep(1)
else:
print('Network is ok. {datetime.now():%Y-%m-%d_%H:%M:%S}')
os.system(f'python {script}')
return
if __name__ == '__main__':
main()
I am trying to make a console for my python applications, but i ran into a problem:
when printing something using the print() function, the text in the input field is also included. This is purely visual, because the program still works.
I tried searching online, but I do not even now what to search for and had no luck.
This is my code. It prints "foo" until the user types "exit":
import multiprocessing as mp
import os
import time
def f(q):
while True:
print(q)
time.sleep(1)
if __name__=="__main__":
p=mp.Process(target=f, args=("foo",))
p.start()
while True:
comm=str(input())
if comm=="exit":
p.terminate()
break
When the program is running, the user can still type, but when the program prints something, it also takes whatever is in the input field at the time:
foo
foo
foo
foo
efoo
xfoo
itfoo
When pressing "enter", the program still registers the input correctly and exits the program.
Here is a modification of your code that only prints foo after you have finished your input typing (i.e., until you hit Enter):
import multiprocessing as mp
from multiprocessing import Queue
def f(q, queue):
while True:
queue.get()
print(q)
if __name__=="__main__":
queue = Queue()
p=mp.Process(target=f, args=("foo", queue))
p.start()
while True:
comm=str(input())
queue.put(None)
if comm=="exit":
p.terminate()
break
If terminating the process is all you want your user to be able to do, then you can instruct them to enter Ctrl+C if they wish to stop the operation and then catch the KeyboardInterrupt exception that comes along with it.
import multiprocessing as mp
import os
import time
def f(q):
while True:
print(q)
time.sleep(1)
if __name__=="__main__":
p=mp.Process(target=f, args=("foo",))
print("Process starting. Use Ctrl+c anytime to stop it!")
p.start()
try:
while True:
input() # Trash command
except KeyboardInterrupt:
print("Terminating process...")
p.terminate()
print("Process terminated...")
If you want to do more complicated commands then a GUI would be your best approach (as mentioned by John)
Sorry I'm new to programming, and don't really understand how this Thread thing works. My goal was for this input to be timed, and I found some code that does that. However, I'm confused about the structure of this Thread because if you are "too slow", the program never continues on to print "checkpoint" as desired. It just sort of... freezes... Why is it getting stuck?
import time
from threading import Thread
answer = None
def check():
# waits for user input for 3 seconds
for i in range(3):
time.sleep(1)
if answer != None:
return
print('too slow')
Thread(target = check).start()
answer = input("Input something: ")
print('checkpoint')
One thing I tried is:
t = Thread(target = check)
t.start()
answer = input("Input something: ")
# also tried t.join()
if t.is_alive:
print('hi')
I tried to solve this program by trying to raise and catch an exception. However, I couldn't catch the exception. How do I catch it? (Or is there another solution to the problem I am having?)
import time
from threading import Thread
answer = None
def check():
# waits for user input for 3 seconds
for i in range(3):
time.sleep(1)
if answer != None:
return
print('too slow')
# was hoping to catch this as an exception
raise TimeoutError
# starts new thread
Thread(target = check).start()
# prompts user for an input
answer = input("Input something: ")
print('checkpoint')
What's good:
When you type something into the input prompt within 3 seconds, it prints "checkpoint" and continues on with code.
What's bad:
If you take "too long", the program prints "too slow!" as expected, BUT then it stops executing code and just sort of... freezes. So to try to fix this, I was hoping to raise a Timeout Error and then catch it, but I don't know how to catch it. This didn't catch the error:
try:
Thread(target = check).start()
except:
pass
This didn't either:
try:
answer = input("Input something: ")
except:
pass
Could I get some help? Thank you!
Edit: Forgot to mention that I am using linux so a lot of the solutions for my application did not work for me like msvcrt or keyboard. And modules that do work for Linux seem not to be "non-blocking."
You should think of the two threads as two separate programs, but sharing the same variables.
Thread 1 consists of everything that isn't indented in your code. It launches a thread, then it waits for user input, then it prints "checkpoint". Then it's done.
Thread 2 consists of the function check. It checks to see if the variable isn't None. If that happens it's done. If that doesn't happen in three seconds, it prints "too slow" and now it's done.
Neither thread "knows" what the other one is doing, except they share one variable, answer.
The program as a whole will exit when all its threads are finished.
That's it. That's what you've written. So if you type something, the program exits because Thread 1 will always exit after you type something. Thread 2 exits once it sees the variable isn't None.
If you don't type anything, Thread 1 will just sit there and wait for you, forever. That's how the input function works. Thread 2 will exit after 3 seconds or less, but that doesn't affect Thread 1.
You can't throw an Exception from one Thread to another. So you can't throw an exception from Thread 2 and have Thread 1 handle it.
Have you tried typing something AFTER the message "too slow" appears? When you do, Thread 1 (and therefore your program) will exit.
The bottom line is that you can't use the input function in cases like this, because that function blocks the flow of its thread until the user types something. There is nothing any other thread can do to make it continue.
DISCLAIMER: THIS DOESN'T ANSWER THE QUESTION BUT IN CASE YOU WANT TO KNOW HOW I GOT AROUND THE "INPUT" THING, HERE IS MY SOLUTION TO THE PROBLEM.
Actually I found something that works! It's a little strange but it works for what I am trying to do, thanks to #rayryeng 's answer here: detect key press in python?.
Problem Statement: Continue the program when 'enter' is pressed, and timeout if input takes too long. This does exactly that, although it displays strangely to the console... PS. I had to run this in my terminal as 'sudo' or it wouldn't work in my scratch file for whatever reason.
import curses
import os
from time import time, sleep
def main(win):
win.nodelay(True) # True turns on "non-blocking"
key=""
win.clear()
win.addstr("Please press 'Enter' to continue:")
start_time = time()
while 1:
end_time = time()
try:
if end_time-start_time > 5: # 5 seconds
return 'You are too slow!'
else:
key = win.getkey()
if key == os.linesep:
return 'OK. Continuing on...'
except Exception as e:
# No input
pass
p = curses.wrapper(main)
print(p) #-> either 'You are too slow!' or 'OK. Continuing on...'
I guess if you actually wanted to store the input you can modify it to be something like this:
def main(win):
win.nodelay(True) # True turns on "non-blocking"
key=""
win.clear()
win.addstr("Please press 'Enter' to continue:")
start_time = time()
while 1:
end_time = time()
try:
if end_time-start_time > 5: # 5 seconds
return 'You are too slow!'
else:
key = win.getkey() # gets a single char
if key: # == os.linesep:
return str(key) # returns that single char
except Exception as e:
# No input
pass
p = curses.wrapper(main)
print(p) #-> either 'You are too slow!' or character entered
And if you want to store more characters you could do something like this (just be aware that it also stores the "enter" key in the resulting string):
import curses
import os
from time import time, sleep
def main(win):
win.nodelay(True) # True turns on "non-blocking"
key=""
win.clear()
win.addstr("Please press 'Enter' to continue:")
start_time = time()
result = key # empty string
while 1:
end_time = time()
try:
if end_time-start_time > 5: # 5 seconds
return 'You are too slow!'
else:
key = win.getkey() # gets single char
result = result + str(key) # adds characters to the empty string
if key == os.linesep: # "new line"
return result
except Exception as e:
# No input
pass
p = curses.wrapper(main)
print(p) #-> either 'You are too slow!' or characters entered
I want to process output from a subprocess and decide to terminate that subprocess once I received sufficient output. My program logic decides when we have enough input.
Example: Wait for a Udev event
try:
for event in sh.udevadm('monitor', _iter=True):
if event matches usb stick added:
print("Ok, I will work with that USB stick you just plugged in!")
break
except:
pass
print("I copy stuff on your USB stick now!")
The 'break' terminates the process but I cannot catch the exception:
What is the correct way to terminate a subprocess or how can I handle the exception?
Maybe you're better off using subprocess.Popen directly instead of sh library.
Something similar to:
$ cat udevtest.py
import subprocess
try:
proc = subprocess.Popen(["udevadm", "monitor"], stdout=subprocess.PIPE,
stderr=subprocess.STDOUT)
while True:
line = proc.stdout.readline()
if line == "" or len(line) == 0:
break # EOF
if line.find("pci0000") != -1: # your trigger
print("TRIGGER %s" % line.strip())
break
proc.terminate()
proc.wait()
except Exception, e:
print(e)
Found a way using interactive callbacks.
http://amoffat.github.io/sh/#interactive-callbacks
Pretty neat, I think.
def wait_for_plugged_in_drive(self):
print("Plugin an external HDD or USB stick.")
sh.udevadm.monitor(_out=self._scan_and_terminate).wait()
def _scan_and_terminate(self, line, stdin, process):
match = re.search('add\\s+/.*/block/sd./(sd..)', line)
if match is not None:
self.device = '/dev/' + match.group(1)
print("USB stick recognized {0}".format(self.device))
process.terminate()
return True
I would like the user to use control-c to close a script, but when control-c is pressed it shows the error and reason for close (which make sense). Is there a way to have my own custom output to the screen rather than what is shown? Not sure how to handle that specific error.
You could use try..except to catch KeyboardInterrupt:
import time
def main():
time.sleep(10)
if __name__ == '__main__':
try:
main()
except KeyboardInterrupt:
print('bye')
use the signal module to define a handler for the SIGINT signal:
import signal
import sys
def sigint_handler(signal_number, stack_frame):
print('caught SIGINT, exiting')
sys.exit(-1)
signal.signal(signal.SIGINT, sigint_handler)
raw_input('waiting...')
For general purpose code, handling the KeyboardInterrupt should suffice. For advanced code, such as threading, it is a whole different story. Here's a simple example.
http://docs.python.org/2/library/exceptions.html#exceptions.KeyboardInterrupt
try:
while 1:
x = raw_input("Type something or press CTRL+C to end: ")
print repr(x)
except KeyboardInterrupt:
print "\nWe're done here."