I'm having a code with a loop asking for some input and then sleeps for some time. The purpose is to prevent for human errors, forcing the user to wait before entering the next input.
The problem is, that python does not ignore the keyboard inputs while time.sleep.
Here is an example code:
from time import sleep
from msvcrt import getch
for i in range(3):
print 'Enter a character'
char = getch()
sleep(2)
print char
When pressing some characters consecutively during time.sleep(), msvcrt.getch() remembers them and the loop runs to the end. I want that every character pressed during sleep will be ignored. How can I do that?
Sorry for wrong answer that i have posted before(as i have deleted though), it is the human level problem that you are asking for.
The program thread is the only event that is put on to sleep, while the keyboard process is still running obviously it will record all the inputs and type after resuming from sleep.
This can't be achieved in this fashion
This is an OS dependant issue, for windows i use this:
import msvcrt
import time
time.sleep(4)
while msvcrt.kbhit():
flush = input()
entry = input("Press enter!")
it just catches all the inputs before asking user for a new input, hope it helps!
Related
I'm trying to write a script so that when I press "0" I will get an output, but I want to work without restarting the script, and I haven't been successful using the keyboard module which I've seen as being the most commonly used for detecting key inputs in Python.
What I have so far is
import keyboard
def goto(linenum):
global line
line = linenum
line = 1
if line == 1:
while True:
if keyboard.is_pressed('0'):
print('pressed 0')
break
goto(1)
What I tried doing was after the loop breaks to refer back to the beginning of the loop and try again from there, however the script ends after I press 0. If I remove the break then it constantly outputs "pressed 0", which is not what I want to happen.
You can use pynput to detect key input.
I would do something like this:
from pynput.keyboard import Key, Listener
def on_press(key):
if str(key).replace("'","") == '0':
print('pressed 0')
listener = Listener(on_press=on_press)
listener.start()
Once you start the listener, it will be always waiting for the key press and you can still add code after. In fact, with this example I recommend to add something after, maybe an input() so the script won't close immediately.
I think there are a few problems going on here.
goto is a pretty bad pattern to use and I don't think there's anything here to make your implementation work. It kinda sounds like you're going for some kind of recursion like approach here where when 0 is pressed, then it does some 'reset' and starts looping again. If that is the case you could do something like this:
def wait_for_zero():
# wait for press here
# Should add some sort of exit check too
# 'reset' logic, if any here
wait_for_zero()
looping with a weak condition is pretty fast cycling and generally a bad idea without some time delay. This is mentioned in the documentation for keybaord. There also is an example in the documentation for keyboard to wait for a keypress: https://github.com/boppreh/keyboard#waiting-for-a-key-press-one-time
It is necessary to make sure that during a certain period of time they are not available for pressing a certain key, for example Space. So that during a break, user clicks are not displayed in any way in the input(). Please suggest a module or a complete solution. Example:
import time
time.sleep(5) # So that during this period of time nothing could be written.
enter = input()
welcome to SO!
Your description is very vague, but assuming you want to prevent a specific keystroke from affecting your program for 5 seconds, this might just work:
import keyboard
import time
time_end = time.time() + 5
while time.time() < time_end:
if keyboard.is_pressed('q'):
pass
replace 'q' with the key you don't want to affect your program. Wherever "pass" is is what will happen if q is pressed within those seconds. I think q will still show up in your program when it's pressed, but wont affect any of your other functions unless you have threading. Sorry if this doesn't help, this is the only thing I could think of.
I need to print out sentence "Hello World" every 10 seconds. However, if the user either 'c' or 'Enter', the program should stop printing the sentence and prompt the user to provide with the another sentence. The user-provided sentence is checked and if the sentence contains any digits, a message shows up: "cannot contain digits". Otherwise a message shows up: "correct sentence". After displaying either of the messages, the program continues printing "Hello World".
Here is the code I have strated with. Any hints on how to continue further would be greatly appreciated.
Thanks!
import threading
def looping():
threading.Timer(10.0, looping).start()
print("Hello World!")
looping()
From my understanding of your assignment's instructions, it looks like you're on the right track with using a timer to print "Hello World"! I'd like to upvote Irmen de Jong's comment on your question with regard to the statement "threads and console input/output don't work nicely together", since I've experienced this myself in C programming.
Once you have the timer going, the text it prints to the screen shouldn't have an effect on responding to keyboard input. If it's really required to respond directly to a keypress of 'c' (not followed by 'Enter', as one would normally have to do when reading input from the keyboard with input()), I recommend following one of the solutions in Python method for reading keypress? to figure out how you would like to implement that.
EDIT: Implementing a solution using a thread-based timer is a bit more tricky than I thought.
As you may have found in your research on this problem, the threading.Timer object has both start() and stop() methods that you can use to control the execution of individual thread timers if you've saved a reference to the timer in a variable (e.g. doing my_timer = threading.Timer(10.0, looping) then calling my_timer.start() to start the timer). If you do this, you may be able to call my_timer.stop() to pause the looping, provided you've kept a proper reference to the current timer instance that you need to stop at that point in time.
To make things a bit easier, I chose to create a global variable PAUSE_LOOPING that, when set to False, will stop a new timer instance from being started when looping is called, thereby halting all further repetitions of the function until PAUSE_LOOPING is set back to True and looping() is called again:
import threading
from msvcrt import getch
PAUSE_LOOPING = False
def looping():
global PAUSE_LOOPING
if not PAUSE_LOOPING:
threading.Timer(10.0, looping).start()
print("Hello World!")
looping()
while True:
# key = ord(getch())
# if key == 13: # Enter
# PAUSE_LOOPING = True
input_string = input()
if input_string == "":
PAUSE_LOOPING = True
else:
PAUSE_LOOPING = False
looping()
Commented out in the last code block is one way to grab a key press directly (without needing to press the 'Enter' key as is required by input()) taken from the stackoverflow question I linked to earlier in my answer. This should work as long as you're using Python for Windows (so you have the MS VC++ runtime library msvcrt installed), but to make the script stop when pressing 'Enter' you can use the standard input() function. In my example, typing any other string of characters before pressing 'Enter' will resume looping after it's been paused.
NOTE: Beware of using Python's IDLE to run this code. It won't work. Instead, you must run it from the command line.
I have a program that takes a very long time to run, and I want it to be able to do what it needs to do but then if the user hits a specific key then I want the loop to break at a certain point. Most Q&A's I have seen pertaining to this problem prompt the user to enter something on each iteration of the loop, however I do not want this. I want the loop to run undisturbed until it needs to quit.
The script will be running as an executable in a command prompt (Windows) so I guess the user could just close the window but I want the loop to break at a certain point. For example:
while True:
print "Doing whatever I feel like"
userinput = raw_input()
if userinput == 'q':
break
So this keeps printing until the user enters 'q', but it prompts the user for input each iteration. How can I avoid this?
If you do not need to stop at a specific point, but just to be able to stop it, you could use a try/except with KeyboardInterrupt (Ctrl-C).
try:
while True:
print "Doing whatever I feel like"
except KeyboardInterrupt:
exit
When the user hits CTRL-C it will exit.
Or this:
import msvcrt
while True:
print "Doing whatever I feel like"
if msvcrt.kbhit(): # True if a keypress is waiting to be read.
if msvcrt.getch()=="q": # will not wait for Enter to be pressed
break
Check msvcrt.
Two possible solutions:
1. Press Ctrl-C to close your program. This also works on linux.
2.
while True:
for _ in range(100)
print "Doing whatever I feel like"
userinput = raw_input()
if userinput == 'q':
break
This only asks the user every 100 iterations.
Start a separate Thread to perform the computation that you need to perform while self.flag == False, and the main program can just sit there waiting for the user input. Once the user input is given, set Thread.flag = True, which will stop the Thread. Wait for the Thread to finish and join, then you can exit from the main program as well.
I've been using the input function as a way to pause my scripts:
print("something")
wait = input("Press Enter to continue.")
print("something")
Is there a formal way to do this?
It seems fine to me (or raw_input() in Python 2.X). Alternatively, you could use time.sleep() if you want to pause for a certain number of seconds.
import time
print("something")
time.sleep(5.5) # Pause 5.5 seconds
print("something")
For Windows only, use:
import os
os.system("pause")
So, I found this to work very well in my coding endeavors. I simply created a function at the very beginning of my program,
def pause():
programPause = raw_input("Press the <ENTER> key to continue...")
and now I can use the pause() function whenever I need to just as if I was writing a batch file. For example, in a program such as this:
import os
import system
def pause():
programPause = raw_input("Press the <ENTER> key to continue...")
print("Think about what you ate for dinner last night...")
pause()
Now obviously this program has no objective and is just for example purposes, but you can understand precisely what I mean.
NOTE: For Python 3, you will need to use input as opposed to raw_input
I assume you want to pause without input.
Use:
time.sleep(seconds)
I have had a similar question and I was using signal:
import signal
def signal_handler(signal_number, frame):
print "Proceed ..."
signal.signal(signal.SIGINT, signal_handler)
signal.pause()
So you register a handler for the signal SIGINT and pause waiting for any signal. Now from outside your program (e.g. in bash), you can run kill -2 <python_pid>, which will send signal 2 (i.e. SIGINT) to your python program. Your program will call your registered handler and proceed running.
I use the following for Python 2 and Python 3 to pause code execution until user presses Enter
import six
if six.PY2:
raw_input("Press the <Enter> key to continue...")
else:
input("Press the <Enter> key to continue...")
print ("This is how you pause")
input()
As pointed out by mhawke and steveha's comments, the best answer to this exact question would be:
Python 3.x:
input('Press <ENTER> to continue')
Python 2.x:
raw_input('Press <ENTER> to continue')
For a long block of text, it is best to use input('Press <ENTER> to continue') (or raw_input('Press <ENTER> to continue') on
Python 2.x) to prompt the user, rather than a time delay. Fast readers
won't want to wait for a delay, slow readers might want more time on
the delay, someone might be interrupted while reading it and want a
lot more time, etc. Also, if someone uses the program a lot, he/she
may become used to how it works and not need to even read the long
text. It's just friendlier to let the user control how long the block
of text is displayed for reading.
Anecdote: There was a time where programs used "press [ANY] key to continue". This failed because people were complaining they could not find the key ANY on their keyboard :)
Very simple:
raw_input("Press Enter to continue ...")
print("Doing something...")
By this method, you can resume your program just by pressing any specified key you've specified that:
import keyboard
while True:
key = keyboard.read_key()
if key == 'space': # You can put any key you like instead of 'space'
break
The same method, but in another way:
import keyboard
while True:
if keyboard.is_pressed('space'): # The same. you can put any key you like instead of 'space'
break
Note: you can install the keyboard module simply by writing this in you shell or cmd:
pip install keyboard
cross-platform way; works everywhere
import os, sys
if sys.platform == 'win32':
os.system('pause')
else:
input('Press any key to continue...')
I work with non-programmers who like a simple solution:
import code
code.interact(banner='Paused. Press ^D (Ctrl+D) to continue.', local=globals())
This produces an interpreter that acts almost exactly like the real interpreter, including the current context, with only the output:
Paused. Press ^D (Ctrl+D) to continue.
>>>
The Python Debugger is also a good way to pause.
import pdb
pdb.set_trace() # Python 2
or
breakpoint() # Python 3
I think I like this solution:
import getpass
getpass.getpass("Press Enter to Continue")
It hides whatever the user types in, which helps clarify that input is not used here.
But be mindful on the OS X platform. It displays a key which may be confusing.
Probably the best solution would be to do something similar to the getpass module yourself, without making a read -s call. Maybe making the foreground color match the background?
user12532854 suggested using keyboard.readkey() but the it requires specific key (I tried to run it with no input args but it ended up immediately returning 'enter' instead of waiting for the keystroke).
By phrasing the question in a different way (looking for getchar() equivalent in python), I discovered readchar.readkey() does the trick after exploring readchar package prompted by this answer.
import readchar
readchar.readkey()
For cross Python 2/3 compatibility, you can use input via the six library:
import six
six.moves.input( 'Press the <ENTER> key to continue...' )
I think that the best way to stop the execution is the time.sleep() function.
If you need to suspend the execution only in certain cases you can simply implement an if statement like this:
if somethinghappen:
time.sleep(seconds)
You can leave the else branch empty.