While loop is not breaking python

Question

I am currently trying to compare the current date and time to a date and time which are written down in another file. For some weird reason the while loop is not breaking but creating an endless loop.

This is what the test.txt file I try to compare the current date and time with contains: 29.10.2021 20:47:47

This is my code (Imagine ga is equal to the data in the test.txt ):

import time
from datetime import datetime
from datetime import timedelta

def background_checker():
    with open('test.txt','r+') as sample:
        while True:
            ga = datetime.now()
            ga = ga.strftime('%d.%m.%Y %H:%M:%S')
            print(ga, end='\r')
            line = sample.readline()
            if line == ga:#if time and date in file equal to the current time and date, the if statement should be triggered. 
                print('alarm')
                break
background_checker()

Am I doing something wrong in my code? If so I would be very glad if someone could explain to me what I've made wrong and how I can solve this problem.

Does this answer your question? [a = open("file", "r"); a.readline() output without \n](https://stackoverflow.com/questions/39921087/a-openfile-r-a-readline-output-without-n) TL;DR when you use `readline()` there's going to be a trailing newline (`'\n'`), so the comparison will always return `False`. — Random Davis, Oct 29 '21 at 19:16
``readline()`` includes the trailing newline. It cannot equal a ``strftime`` without a trailing newline. — MisterMiyagi, Oct 29 '21 at 19:17
There are 2 things I want to say. 1. if the time in your test.txt file is not equal to the time.now() you will never break 2. Consider using the keyword 'in' instead `ga in line` if the line you read in is longer and contains formatting characters — Shabbir Hussain, Oct 29 '21 at 19:17
everytime you run this python file the line `ga = datetime.now()` will assign a different value to the variable `ga` — Shabbir Hussain, Oct 29 '21 at 19:21
@ShabbirHussain the content of the file look like this:`29.10.2021 20:47:47` — scripter2, Oct 29 '21 at 19:22
@ShabbirHussain yup until it matches the content of the file. Then it should break — scripter2, Oct 29 '21 at 19:23
@ShabbirHussain the current day, month, year, hour, minute and second. — scripter2, Oct 29 '21 at 19:24
@ShabbirHussain there is no exact string because ga is changing every iteration of the while loop — scripter2, Oct 29 '21 at 19:26
the thing is that `ga` will always be increasing. What if the time in your file is in the past? — Shabbir Hussain, Oct 29 '21 at 19:28
So just to be clear: The file contains *only* a datetime string like ``29.10.2021 20:47:47`` without a trailing newline? And it represents a datetime that has not passed yet but will happen soon? — MisterMiyagi, Oct 29 '21 at 19:30

score 1 · Answer 1 · answered Oct 29 '21 at 19:40

You are trying to create an alarm program but you're comparing strings using string equality. A better approach is to compare datetime objects.

import time
from datetime import datetime
from datetime import timedelta

def background_checker():
    format = '%d.%m.%Y %H:%M:%S'
    with open('test.txt','r+') as sample:
        while True:
            ga = datetime.now()
            print(ga)
            line = sample.readline()
            alarm_time = datetime.datetime.strptime(line, format)     
            if ga > alarm_time: #if time and date in file equal to the current time and date, the if statement should be triggered. 
                print('alarm')
                break
background_checker()

While loop is not breaking python

1 Answers1