Problem calling fucntion with lambda along with QTimer.singleShot

Question

I tried to call the function using delay time and taking the help of QTimer.singleShot function but is not getting any output.

from PyQt5.QtCore import QTimer

list1=[1,2,3,4,5]

delay = 2500

def calling_func():

    if list1:

        list_item = list1.pop()

        QTimer.singleShot(delay, lambda: target_func(list_item))

def target_func(list_item):

    print("fid= ",list_item)

    QTimer.singleShot(delay, calling_func)

calling_func()

I am expecting to output the list_item value one by one in the target_func but my function is not being called.

Answer 1

The asynchronous elements of Qt such as signals and timers use the eventloop for their execution, in your case there are none so it fails. The solution is to create a Q{Core, Gui} Application:

from PyQt5.QtCore import QCoreApplication, QTimer

list1=[1,2,3,4,5]

delay = 2500

def calling_func():

    if list1:

        list_item = list1.pop()

        QTimer.singleShot(delay, lambda: target_func(list_item))

def target_func(list_item):

    print("fid= ",list_item)

    QTimer.singleShot(delay, calling_func)

app = QCoreApplication([])

calling_func()

app.exec_()

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