Is it possible to change a value when script is running inside a loop?
import sys
inputValue = 120
def changeValue(value):
inputValue = value
def main():
if inputValue == 0:
print 'Value is'+str(inputValue)
if __name__ == '__main__':
while True:
main()
I think to change executing the script python app.py calling the function python app.py changeValue 23 but I dont know how exactly it'd work.
There are many ways to control a running program, but to a first approximation all of them involve alternating between doing some work and checking for input. A very simple approach would be something like this:
import string
value = 1
def checkChangeValue():
newValue = input()
if newValue.isdigit():
global value
value = int(newValue)
def main():
print("Value is {}".format(value))
def loop():
main()
checkChangeValue()
if __name__ == '__main__':
while True:
loop()
This runs the main function ("do some work") and then checkChangeValue ("check for input") over and over. This may not do what you want, though, because input() waits for you to type something and hit enter, so it will block the execution of main. To get around this you could add threads:
import string
import threading
value = 1
def checkChangeValue():
global value
while True:
newValue = input()
if newValue.isdigit():
value = int(newValue)
def main():
print("Value is {}".format(value))
if __name__ == '__main__':
threading.Thread(target=checkChangeValue).start()
while True:
main()
Either of these methods may work, depending on your needs. For a more sophisticated approach you might look at the pynput library, which lets you interact with your program through keyboard or mouse input.
There are many other different ways of controlling a running program, too! You could communicate with your program through files, pipes, sockets, shared memory, etc. This in general is called "Inter-process communication" or IPC.
You have to declare inputValue as a global variable using the global statement inside the changeValue function in order for assignment statements to that variable inside the function to be applied to inputValue as a global variable; otherwise the assignment would be made to inputValue as a variable local to changeValue instead:
def changeValue(value):
global inputValue
inputValue = value
Note that any use of a global variable other than for the purpose of read-only application-wide configuration is generally discouraged. You should consider making your global variable a local one and pass it around as a function argument and as a returning value instead, e.g.:
import sys
def changeValue(value):
return value + 1
def main(value):
value = changeValue(value)
print('Value is %d' % value)
if __name__ == '__main__':
inputValue = int(sys.argv[1])
while True:
main(inputValue)
python app.py 'number' ? Considering the script is running
sys.argv[1]. I've updated the example in my answer to reflect that.