如何使用线程从while循环中获取参数的值？

Question

I am trying to obtain the changing value of argument (self.num), which is changing in a while loop of a separate thread, every time I need it. However, I always get only zero.

from time import sleep
from threading import Thread


class Number:
    def __init__(self):
        self.num = 0

    def trend(self):
        while 1:
            self.num += 1

    def trend1(self):
        return self.num

if __name__ == '__main__':
    while 1:
        Thread(target=Number().trend).start()
        print(f"{Number().trend1()=}")
        sleep(0.1)
        print(f"{Number().trend1()=}")

Answer 1

The very first Number defined in Thread can never be referred. Also, in your while loop, you defined another 2 Number s that are independent to the Thread.

you just need one Number to do the job:

if __name__ == '__main__':
    number = Number()                # save an Number() object as param
    th = Thread(target=number.trend) # create a Thread for its trend()
    th.daemon = True                 # (optional) Thread dies with code
    th.start()                       # start the Thread
    while 1:                          
        print(f"{number.trend1()=}") # call the trend1() in number
        sleep(0.1)
        print(f"{number.trend1()=}")

now, number holds the Number() object for the Thread and counter.