Q:

Thread is printing two times at same loop

Inside of each loop the thread is printing two times. In this case, it prints two times to each 3 seconds. I want that it prints only one time.
on Flask:
from flask import Flask
import threading
from time import sleep

app = Flask(__name__)

@app.route('/')
def index():
  return 'ok'

def func():
  count = 1
  while True:
    print(count)
    count += 1
    sleep(3)

t = threading.Thread(target=func)
t.setDaemon(True)
t.start()

if __name__ == '__main__':
  app.run(debug=True)

output:
1
1
2
2
3
3
...

expected output:
1
2
3
...

A:

I figured out the why.
When run modules like threading and apscheduler in Flask with debug mode: on ...
it happens.

