For Loop assigns only the latest value from List

[Caliban86]

Hello Guys, im really new here and i am still working on the Basics of Python but i got to a Problem, where i do absolutely have no idea, what is wrong here.

I want to assign a QThread Call to 6 Buttons created in QTDesigner. I use a For-Loop with it, because the Number of the Buttons can be variabel. Because i can not call the QThread from a Lambda call directly, i try to put the calls in a List instead of creating a variable for any of them:

a = number_buttons + 1
self.move = []
print(self.move)
  for element in range(1, a):
  self.move.append(move_stepper_thread(anotherlist[element], 1000))

so this give me a list with the following content:

[<__main__.move_stepper_thread(0x1ebe2b286f0) at 0x000001EBE3A0BF80>, <__main__.move_stepper_thread(0x1ebe2b25110) at 0x000001EBE39301C0>, <__main__.move_stepper_thread(0x1ebe2b25050) at 0x000001EBE3899F80>, <__main__.move_stepper_thread(0x1ebe2b24c10) at 0x000001EBE3A5FA80>, <__main__.move_stepper_thread(0x1ebe2b24bd0) at 0x000001EBE3A5FF40>, <__main__.move_stepper_thread(0x1ebe2b24bf0) at 0x000001EBE3A5F440>, <__main__.move_stepper_thread(0x1ebe2b24d50) at 0x000001EBE3A70A80>]

now i have another loop, where i assing the list values to the buttons:

for element in range(1, a):
                indexx = element - 1
                getattr(self, "gleis_btn_" + str(element)).clicked.connect(lambda: self.move[indexx].start())

so here all the buttons with name gleis_btn_X (x for number) get connected with call for the QThread and the indexx gives the number from the list.

But here begins my Problem, after the For-Loop, every Button gets the last index of the self.move[] list. When i change the entry self.move[indexx] manually to self.move[0] or self.move[1], the correct entry from the list will be assigned to the button. Even when i create the Buttons all manually like:

getattr(self, "gleis_btn_" + str(1)).clicked.connect(lambda: self.move[0].start())
getattr(self, "gleis_btn_" + str(2)).clicked.connect(lambda: self.move[1].start())
getattr(self, "gleis_btn_" + str(3)).clicked.connect(lambda: self.move[2].start())

It works fine! But when i try to assign the Lambda Call via the For-Loop, every Button get only the last Value of the self.move[] List. But Why?

i already tried it with a 1-Liner on the Lambda Call like:
getattr(self, "gleis_btn_" + str(1)).clicked.connect(lambda: move_stepper_thread(gleis[element], 1000).start())

But in this case when i press the Button on the GUI, it crashes and say "QThread: Destroyed while thread is still running". But when i only do the self.move.start() call it works and the Thread runs.

I hope you can help me here, it drives me crazy, because i do not understand why it will not work... the indexx value increases by 1 in every for-loop and it begins on 0, this is why i added the indexx = element - 1 at the beginning, so that the indexx is always one less then the given range.

Thank you very much and greetings from Germany,
Caliban.

[menator01]

Please use the bb tags when posting code.
I would learn to code in qt without the designer. It uses unnessary code.
What does move_stepper_thread?
Post what errors you are getting.

[Caliban86]

Please use the bb tags when posting code.
I would learn to code in qt without the designer. It uses unnessary code.
What does move_stepper_thread?
Post what errors you are getting.

Thank you, i edited my post and put the Code into Tags.

In the example the Thread does nothing then print the given Parameters:

class move_stepper_thread(QThread):

    def __init__(self, targetposition, time):
        #QThread.__init__(self)
        super().__init__()
        self.targetPosition = targetposition
        self.time = int(time)

    def run(self):

        print("Test: "+str(self.targetPosition))

Later this Function is to send a Position via Serial Communication to an Arduino Nano. This is already working. I try to rewrite the Programm because before i called all Functions outside of the MainWindow Class. I used the Python Threading before and it worked okay, but i need to append in the Thread Function a Text to a Log-Box in the MainWindow GUI and this does not work or i did not find a way to Emit a Signal from a normal Python Thread. Now i want to rewrite everything to use QThreads instead, which should better work in combination with QT and Signals/Slots(?!). But this drives me just crazy here.

The Thread Function itself is working, when i manually set the Lambda Call, it prints exactly the given Parameter, so it works. But when i try to assign the Calls via the Loop, it always print the same thing on every Button i press.

Edit:
i found a Solution here, i have not really understand why it is working but i changed the For-Loop to:

for element2 in range(1, a):
                i = element2 -1
                x = element2
                getattr(self, "gleis_btn_" + str(x)).clicked.connect(lambda state, i2=i: self.move[i2].start())

i added the lambda state, i2=i and use that i2 variable and with this, it works.

[deanhystad]

When you do this:

lambda: self.move[indexx].start()

you create a function and a closure to execute the function using the variable indexx. What is the value of indexx? Like every variable, its value is the last value it was assigned. In your program indexx was last assigned the value a-2.

When you do this:

lambda state, i2=i: self.move[i2].start()

you create a function and a variable, i2. i2 is assigned the value of indexx at the time the lambda function is created.

I prefer using a partial function for something like this.

import tkinter as tk
from functools import partial


root = tk.Tk()
variable = tk.IntVar(root, 0)
tk.Label(root, textvariable=variable).pack()
for i in range(5):
    tk.Button(
        root, text=str(i), command=partial(variable.set, i)
    ).pack(side=tk.TOP, expan=True, fill=tk.X)
root.mainloop()