Problem calling fucntion with lambda along with QTimer.singleShot

Question

I tried to called a function with delay time with of help of QTimer.singleShot function but is not yielding 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 list_item value one by one in target_func but the 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_()