What is the best way to quickly exit a Python program with an infinite loop that uses curses module?
I've tried adding nodelay() method coupled with this at the end of the loop:
if screen.getch() == ord('q'):
break
However, it takes 2-3 seconds to make all the function calls on one iteration of the loop. And because of the application, it doesn't make sense to run the loop more often than every 5 second. This means that in order for my way of exiting the program to work, I sometimes have to press and hold 'q' for 2-8 seconds.
My code looks like this:
import curses
import time
def main(screen):
refresh_rate = 5
screen.nodelay(1)
# Infinite loop. Displays information and updates it
# every (refresh_rate) # of seconds
while True:
# Makes several http requests
# and passes responses through multiple functions
# Escape infinite loop
if screen.getch() == ord('q'):
break
# Wait before going through the loop again
time.sleep(refresh_rate)
if __name__ == "__main__":
curses.wrapper(main)
My other solution was to replace while True with:
loop = 1
while loop:
#Loop code
if screen.getch() == ord('q'):
loop = -1
This way, there is no need to press and hold 'q' to exit the program. But it can still take up to 8 seconds to exit after pressing 'q' once.
For obvious reasons, this doesn't seem to be the best way of exiting the program. I am pretty sure there should be a better (faster) solution.
Other than that, the program works fine. It's 2 files with more than 300 lines, so I am posting just the relevant parts of the code with my attempted solutions.
Given that you have nodelay already, the usual approach is to use napms with a small (20-50 milliseconds) time, and addressing your 5-seconds goal, to run the functions after several (10-25) repetitions of the getch/napms loop.
Mixing curses and standard I/O doesn't really work well unless you take care to flush things when switching between the two.
What's probably happening is that your 'q' is coming in between the getch() and the sleep calls. Given that getch() takes a fraction of a second to execute and sleep locks the program for 5 seconds, it's very likely that any time you press a key you're going to wait.
The easiest way to exit any python script is to press Ctrl-C - it spawns a KeyBoardInterrupt exception that can be handled like:
try:
while True:
do_something()
except KeyboardInterrupt:
pass
Granted, if this is meant to be a user-facing application, that might not be sufficient. But it's also unlikely that any production application would operate without a full event loop and a UI that would allow them to exit.
Last, if you want another way of doing what you're already doing, you can use:
import sys
sys.stdin.read(1)
To read 1 bye of user input at a time. I'd go for the Ctrl-C route, if I were you.
Related
I'm making a Discord bot with a lot of commands that take a while to finish (like loops) so I'd like to also have a command that stops any actively running code. I've tried sys.exit but I don't want to have to restart the program each time before it will take another input. Anyone know what I can do?
It will depend on the way your code is formatted, but you will probably want to use functions that utilize boolean or return statements:
def foo():
if end_this:
return
# stuff
If you have some tracking boolean end_this that is set to True, the function foo() will not execute everything below. Alternatively, you could use a while-loop with a break in your code:
def foo():
while True: # runs forever unless ended
# stuff
break
Now, foo() will continue indefinitely until the break statement is reached. An if-statement can enclose the break, setting some logic on when the break occurs. Again, this may require a main() function to handle the calls and ends of your previous functions, but it would allow following code/functions to execute.
I have a small script where I have a continuous loop. The loop runs and I expect that the user will give an input whenever he wants. I want to check if the user wrote something in the console, if yes, I will do something extra, if not, the loop continues.
The problem is that when I call the input() function, the program waits for user input.
The code that I will use here will be just a simple version of my code to show better what is my problem.
i=0
while True:
i+=1
if 'user wrote a number':
i+= 'user's input'
The objective is to not stop the loop if the user do not input anything. I believe this is a simple thing but I didn't find an answer for this problem.
Thank you for your time!
You can execute the background task (the while True) on a separate thread, and let the main thread handle the input.
import time
import threading
import sys
def background():
while True:
time.sleep(3)
print('background task')
def handling_input(inp):
print('Got {}'.format(inp))
t = threading.Thread(target=background)
t.daemon = True
t.start()
while True:
inp = input()
handling_input(inp)
if inp == 'q':
print('quitting')
sys.exit()
Sample execution (lines starting with >> are my inputs):
background task
>> a
Got a
>> b
Got b
background task
>> cc
Got cc
background task
background task
>> q
Got q
quitting
Process finished with exit code 0
The only caveat is if the user takes longer than 3 seconds to type (or whatever the value of time.sleep in background is) the input value will be truncated.
I'm don't think you can do that in one single process input(), because Python is a synchronous programming languaje,the execution will be stoped until input() receives a value.
As a final solution I'd recommend you to try implement your functions with parallel processing so that both 'functions' (input and loop) can get executed at the same time, then when the input function gets it's results, it sends the result to the other process (the loop) and finish the execution.
I have written some code to make the turtlebot turn around. The code is working. What I want to know is how fast the turtlebot is running and how I can control it. Forexample, how can I ensure that the turtlebot turns 5 degrees in one minute?
Last part of the question. After pressing Ctrl-C, the turtlebot stops but the script keeps running. Why? and how can I stop that?
this post does not really help.
went through this post .Does that mean that the while loop below runs 5 times a second regardless of the values I put in the for loops? Or does it mean ROS tries its best to make sure that the loop runs 5 times a second to the best of my machine's ability?
Thank you very much.
# 5 HZ
angle = 5
r = rospy.Rate(5);
while not rospy.is_shutdown():
# code to turn
for x in range(0,100):
rospy.loginfo("turn")
turn_cmd.angular.z = radians(angle)
new_angle = (angle + new_angle) % 360
self.cmd_vel.publish(turn_cmd)
r.sleep()
# code to pause
for x in range(0,100):
rospy.loginfo("stop")
turn_cmd.angular.z = radians(0)
self.cmd_vel.publish(turn_cmd)
r.sleep()
def shutdown(self):
# stop turtlebot
rospy.loginfo("Stop turning")
self.cmd_vel.publish(Twist())
rospy.sleep(1)
According to ROS Wiki, the rospy.Rate convenience class makes a best effort to maintain the loop running at the specified frequency by considering the execution time of the loop since the last successful r.sleep(). This means in your case: as long as the code execution time within the loop does not exceed 1/5 seconds, rospy.Rate will make sure the loop runs at 5Hz.
Regarding the script not stopping when pressing Ctrl-C:
KeyboardInterrupt will be handled differently than in normal Python scripts when using rospy.
rospy catches the KeyboardInterrupt signal to set the rospy.is_shutdown() flag to true. This flag is only checked at the end of each loop, therefore if pressing Ctrl-C during the for-loop executions, the script cannot be stopped because the flag is not checked immediately.
A manual way to signal a shutdown of the node is to use rospy.signal_shutdown(). For this, the disable_signals option needs to be set to true when initializing the ROS node (see Section 2.3 here). Note that you will additionally have to manually invoke the correct shutdown routines to ensure a proper cleanup.
I am trying to complete a simple GUI automation program that merely opens a web page and then clicks on a specific spot on the page every 0.2 seconds until I tell it to stop. I want my code to run and have its loop run infinitely until a keybind I specify breaks the loop (or entire program). I started out with the classic, KeyboardInterrupt, which enables CTRL+C to exit a program. Here is what I thought my final code would look like:
import webbrowser, pyautogui, time
webbrowser.open('https://example.com/')
print('Press Ctrl-C to quit.')
time.sleep(5)
#pyautogui.moveTo(1061, 881)
try:
while True:
time.sleep(0.2)
pyautogui.click(1061,881)
except KeyboardInterrupt:
print('\nDone.')
Everything about the code works, except the fact that I can't exit it once the clicking loop starts. Keyboard interrupt and using CTRL-C to exit do not work at all for this script, for whatever reason.
I merely want to be able to press "escape" (or any other key) to exit the loop (or the program altogether) - just any way to make the loop exit and stop. Right now it runs ad infinitum, but I want a simple keybind macro to be able to stop/break it.
I've tried using getch to keybind the escape key to cause a break, but to no avail:
import webbrowser, pyautogui, time, msvcrt
webbrowser.open('https://example.com')
print('Press Ctrl-C to quit.')
time.sleep(5)
#pyautogui.moveTo(1061, 881)
try:
while True:
time.sleep(0.2)
pyautogui.click(1061,881)
if msvcrt.kbhit():
key = ord(readch())
if key == 27:
break
I'm surprised it's been so hard to do this in Python. I've checked out a lot of similar problems across Stackoverflow, but with unsatisfactory answers, and none that solve my problem, unfortunately. I've been able to do things like this in simpler coding languages like AuotHotKeys with ease. I feel like I'm dancing around the solution. Any and all help would be wonderfully appreciated! Thanks in advance.
If I understood correctly, you want to be able to stop your program by pressing a key on your keyboard.
To make you create a thread that will check in background if you press the key in question.
A little example:
import threading, time
from msvcrt import getch
key = "lol"
def thread1():
global key
lock = threading.Lock()
while True:
with lock:
key = getch()
threading.Thread(target = thread1).start() # start the background task
while True:
time.sleep(1)
if key == "the key choosen":
# break the loop or quit your program
Hope its help.
Is there an easy way to execute time delay (like time.sleep(3)) between every statement of Python code without having to explicitly write between every statement?
Like in the below Python Script which performs certain action on SAP GUI window. Sometimes, the script continues to the next statement before the previous statement is complete. So, I had to add a time delay between every statement so that it executes correctly. It is working with time delay, but I end up adding time.sleep(3) between every line. Just wondering if there is a better way?
import win32com.client
import time
sapgui = win32com.client.GetObject("SAPGUI").GetScriptingEngine
session = sapgui.FindById("ses[0]")
def add_record(employee_num, start_date, comp_code):
try:
time.sleep(3)
session.findById("wnd[0]/tbar[0]/okcd").text = "/npa40"
time.sleep(3)
session.findById("wnd[0]").sendVKey(0)
time.sleep(3)
session.findById("wnd[0]/usr/ctxtRP50G-PERNR").text = employee_num
time.sleep(3)
session.findById("wnd[0]").sendVKey(0)
time.sleep(3)
session.findById("wnd[0]/usr/ctxtRP50G-EINDA").text = start_date
time.sleep(3)
session.findById("wnd[0]/usr/tblSAPMP50ATC_MENU_EVENT/ctxtRP50G-WERKS[1,0]").text = comp_code
time.sleep(3)
session.findById("wnd[0]/usr/tblSAPMP50ATC_MENU_EVENT/ctxtRP50G-PERSG[2,0]").text = "1"
time.sleep(3)
session.findById("wnd[0]/usr/tblSAPMP50ATC_MENU_EVENT/ctxtRP50G-PERSK[3,0]").text = "U1"
time.sleep(3)
session.findById("wnd[0]/usr/tblSAPMP50ATC_MENU_EVENT").getAbsoluteRow(0).selected = True
time.sleep(3)
return "Pass"
except:
return "failed"
The right way to do what you asked for is almost certainly to use the debugger, pdb.
The right way to do what you want is probably something completely different: find some signal that tells you that the step is done, and wait for that signal. With problems like this, almost any time you pick will be way, way too long 99% of the time, but still too short 1% of the time. That signal may be joining a thread, or waiting on a (threading or multiprocessing) Condition, or getting from a queue, or awaiting a coroutine or future, or setting the sync flag on an AppleEvent, or… It really depends on what you're doing.
But if you really want to do this, you can use settrace:
def sleeper(frame, event, arg):
if event == 'line':
time.sleep(2)
return sleeper
sys.settrace(sleeper)
One small problem is that the notion of line used by the interpreter may well not be what you want. Briefly, a 'line' trace event is triggered whenever the ceval loop jumps to a different lnotab entry (see lnotab_notes.txt in the source to understand what that means—and you'll probably need at least a passing understanding of how bytecode is interpreted, at least from reading over the dis docs, to understand that). So, for example, a multiline expression is a single line; the line of a with statement may appear twice, etc.1
And there's probably an even bigger problem.
Sometimes, the script continues to next step before the previous step is fully complete.
I don't know what those steps are, but if you put the whole thread to sleep for 2 seconds, there's a good chance the step you're waiting for won't make any progress, because the thread is asleep. (For example, you're not looping through any async or GUI event loops, because you're doing nothing at all.) If so, then after 2 seconds, it'll still be just as incomplete as it was before, and you'll have wasted 2 seconds for nothing.
1. If your notion of "line" is closer to what's described in the reference docs on lexing and parsing Python, you could create an import hook that walks the AST and adds an expression statement with a Call to time.sleep(2) after each list element in each body with a module, definition, or compound statement (and then compiles and execs the result as usual).
Anything you want to happen in a program has to be explicitly stated - this is the nature of programming. This is like asking if you can print hello world without calling print("hello world").
I think the best advice to give you here is: don't think in terms of "lines", but think in term of functions.
use debugging mode and watch each and every line executing line by line.