Python: How to stop function execution from outside - python

I have the following problem:
i have a GUI with two Buttons: "Run" and "Stop".
When I press Button "Run", function a will be executed.
How can I stop the execution by pressing Button "Stop", without any if statements? In function a, there are a ton of mathematical calculations so if I would just border the code inside the function a with a loop and check once per loop-pass if the Button "Stop" was pressed, it would take too much time.
I want to stop the execution of the function a right now, not when the whole calculations are finished. So for example to border the code inside the function with try/catch but raising the exception outside of the function, then I could stop the execution of the function everytime I want, not until the if-statement would be reached. I allready tried to solve the Problem with a thread but it doesn't work because I don't know, how to start a thread with commit some parameters to the Custom thread-class.
Here a small Pythoncode that should show what I mean:
class GUI():
def __init__(self):
#Initialization of Button "Run",connect Button "Run" to function a
#Initialization of Button "Stop",connect Button "Stop" to function b
def a(self):
"""calculation of a ton of mathematical stuff, can take MORE THAN
FIVE MINUTES to be finished, could be grouped in
individual functions to border the function-calls with try/catch,
but would be inefficient and inelegant"""
pass
def b(self):
"""Should stop the execution of function a immediately """

Related

How can I execute multiple tasks with a function when pressing a button in Tkinter?

So, my plan is to create one of those games where a sequence is shown on the screen and you have to click the correct buttons, following the sequence. I'm going to use Tkinter for this project. Here's some explanation: When any buttons is clicked, a function will be executed with a parameter that will tell which button has been clicked, and then the function will check whether it's the correct button or not.
THE PROBLEM: if the user clicked the right button, this function will call a second function to show the next buttons of the sequence. The thing is that it should take some time to display this, and meanwhile the tkinter button remains 'clicked'. I don't want it to happen, also because you cannot execute other tasks, such as leaving the game or restarting the round, while this is happening.
Here I have a simple example to show you the problem, if you couldn't see it yet:
import tkinter as tk
from time import sleep
def func():
print('hi')
func2()
def func2():
print('hi2')
for num in range(3, 11):
sleep(1)
print('hi' + str(num))
wn = tk.Tk()
b1 = tk.Button(wn, command=func)
b1.pack()
wn.mainloop()
In this case, the code should print 'hi' + the numbers from 1 to 10 when the button is pressed. However, the things I've said previously happen.
How can I make this example above work correctly and also my project?
You can either use threads or you can define func3 which runs func1 and func2.

Pausing Python Code When Console Output Has Been Re-Routed to GUI

I borrowed a design that I found on stackoverflow to redirect console output to a PyQt5 GUI textEdit widget. This works fine, but the text is not displayed in "real-time". It seems to output the text to the GUI once a process has completed. This has not been a problem until I tried to use time.sleep(secs) to print something, pause, then print something else. What ends up happening is that the program pauses for secs, then it prints all of the statements at once.
This class is in the mainWindow file for the GUI:
class EmittingStream(QtCore.QObject):
textWritten = QtCore.pyqtSignal(str)
def write(self, text):
self.textWritten.emit(str(text))
This is in the __init__ method of my event handling file:
sys.stdout = EmittingStream(textWritten=self.normalOutputWritten)
self.case_setup_console.setReadOnly(True)
self.main_console.setReadOnly(True)
This function is in the main class of event handling file (outside __init__):
def normalOutputWritten(self, text):
"""Append text to the QTextEdit."""
# Maybe QTextEdit.append() works as well, but this is how I do it:
cursor = self.case_setup_console.textCursor()
cursor.movePosition(QtGui.QTextCursor.End)
cursor.insertText(text)
self.case_setup_console.setTextCursor(cursor)
self.case_setup_console.ensureCursorVisible()
This works as intended to re-route the output to the text edit widget self.case_setup_console. But, when I try to run a code such as:
print('This is the first message')
time.sleep(5)
print('This should print 5 seconds later')
What happens is that the program waits 5 seconds, then it prints both statements together.
When programing for GUI code, there is a fundamental shift in how the program is designed. To make it short: after building and initialisation, the program is all the time running in an "event loop" provided by the GUI framework, and your code is only called when specific events take place.
That is in contrast with a terminal application where your code is running all the time, and you tell when to do "print"s, "input"s and pauses with "time.sleep".
The GUI code is responsible for taking notes of events (keyboard, UI, network, etc...), redrawing window contents and calling your code in response to events, or just when it is time to redraw a content that is defined in your code (like updating a background image).
So, it can only render the text that is supposed to show up in a window, with your redirected "print", when the control is passed back to its event loop. When you do time.sleep you pause the return - no code in the event loop is run, and it can't, of course, do any screen drawing.
What is needed is that you write your pauses in the program in a way that during the pause, the GUI event loop is running - not "time.sleep", that just suspends your whole thread.
In Qt the way to do that is create a QTimer object to call the code you want to use to print text at a particular moment, and then just surrender the execution to the the QtMainloop by returning from your function.
Thanks to Python's support for nested functions, that can be done in painless ways, even using lambda functions when setting the timer itself.
...
print('This is the first message')
timer = QtCore.QTimer
timer.singleShot(5000, lambda *_: print('This should print 5 seconds later'))
Should work for the given example. (The call, as usual for UIs, takes the pause time in miliseconds rather than in seconds).
If you will need to schedule more text to be printed after each phrase is output, you will need to call the scheduling inside the callback itself, and will need a little more sophistication, but it still could be as simple as:
phrases = iter(("hello", "world", "I", "am", "talking", "slowly!"))
timer = QtCore.QTimer()
def talker(*_):
phrase = next(phrases, None)
if not phrase:
return
print(phrase)
timer.singleShot(1000, talker)
timer.singleShot(1000, talker)
(Note that there is nothing special about the *_ parameter name either: I am just indicating that there might be any number of positional arguments for the callback - (The "*" part, that is Python syntax) - and that I won't care about then (I call the argument sequence as "_" to indicate I don't care how this is called, as it won't be used anyway - that is a coding convention) )
The iter and next calls are more "Python dialect" than one might be used, but one could just use a list and a counter up to the list length all the same.

Python: How can I delay the execution of second function by one second

So I want to know how I can make a delay between executing two functions. The goal is to replace regular, blank button by black after it was on screen for one second. My current program, simplified looks like this, and it just delays the the execution of CreateInterface():
class Program(Frame):
def __init__(self,root):
self.root=root
self.root.title('Test')
super().__init__(self.root)
self.grid()
self.Start()
return
def Start(self):
startbtn=Button(self,width=5, font=('Calibri',16,'bold'), height=2, text='start',command=lambda:self.CreateInterface())
startbtn.grid(row=1,column=1)
def CreateInterface(self):
time.import
btn1=Button()
btn1.grid(row=1,column=1)
time.sleep(10)
self.Function2(self)
return
def Function2(self):
btn2=Button(bg='black')
btn2.grid(row=1,column=1)
return
In a GUI interface, calling time.sleep makes the whole process wait, so the application appears to freeze. With Tk in Python, a way to do is to use the Tk after method on a window or frame, and then call a function that makes the necessary change to your Button. There are examples of how to do this at How to create a timer using tkinter
Use time.sleep to pause program execution for a certain amount of time. If you wanted to pause for 1 second after calling CreateInterface, change it to this:
def CreateInterface(self):
btn1=Button()
btn1.grid(row=1,column=1)
time.sleep(10)
self.Function2(self)
time.sleep(1)
Don't forget to import time when you do this.

Partial parameters are duplicated

I am creating on_press callbacks for button behavior objects inside a loop and for some reason all of the parameters for the partial stay the same as the parameters for the last partial created.
shortened example of creation:
(button is a class that implements button behaviour)
for button in list:
button.on_press=partial(my_func, button, button.arg1, button.arg2)
the problem is that the arguments arg1 and arg2 stay the same as the last iteration of the loop instead of being updated. so when I press the buttons (doesn't matter which one) the callback is called as if I pressed the last button.
why does this happen / how can I fix this?

How is tkinter code executed?

I am writing a program using tkinter, but I do not understand how it works. Normally, code is executed top-down, but with tkinter it obviously does not.
For example, I have bound a function to the left mouse button, and this function is executed every time I click the button. But how is the other code around that treated? My problem is that I in the start of my program initialize a variable that is used as an argument in the bound function, and then it is changed in the function and returned. But every time the function is called, the variable seems to be reset to its initial value.
Does anyone know why this is?
I have it written like this:
var = "black"
var = c.bind("<Button-1>", lambda event: func(event, arg=var))
The function "func" changes var and returns it, but the next time I press the button the variable is always "black".
Thanks in advance!
Tkinter does indeed run top down. What makes tkinter different is what happens when it gets to the bottom.
Typically, the last executable statement in a tkinter program is a call to the mainloop method of the root window. Roughtly speaking, tkinter programs look like this:
# top of the program logic
root = tkinter.Tk()
...
def some_function(): ...
...
some_widget.bind("<1>", some_function)
...
# bottom of the program logic
root.mainloop()
mainloop is just a relatively simple infinite loop. You can think of it as having the following structure:
while the_window_has_not_been_destroyed():
event = wait_for_next_event()
process_event(event)
The program is in a constant state of waiting. It waits for an event such as a button click or key click, and then processes that event. Conceptually, it processes the event by scanning a table to find if that event has been associated with the widget that caught the event. If it finds a match, it runs the command that is bound to that widget+event combination.
When you set up a binding or associate a command with a button, you are adding something to that table. You are telling tkinter "if event X happens on widget Y, run function Z".
You can't use a return result because it's not your code that is calling this function. The code that calls the function is mainloop, and it doesn't care what the function returns. Anything that gets returned is simply ignored.

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