在循环函数中调用时，Python全局变量不变

Question

Program: to get the next check time from a file 'config.txt', if the current time is the same or greater time than the next check time then the program should enter a constant loop, of:

checking something, doing an action, then recording the next check time to the file, then waiting for the next check time is the same or greater then repeat.

Problem: The variables outside of the functions are staying the same when being called. See Variable: msg_time which displays the time does not change while in the function

File named config.txt contains:

 nextchecktime='2016, 03, 09, 10, 38, 27, 508749' 

time format is %Y, %m, %d, %H, %M, %S, %f in UTC time

Code:

import datetime, time, re

msg_time = datetime.datetime.now().strftime('%H:%M %d-%M-%y : ') # Date format prefix at the start of each message to user.


#Get last time program run from config file 

config_file = open('config.txt', 'r+')
config_data = config_file.read() 
config_file.close()

next_check_time_regex = re.compile(r'nextchecktime\=\'((.)*)\'') # Find nextchecktime= line in config file
mo = next_check_time_regex.search(config_data)

next_check_time = datetime.datetime.strptime(mo.group(1), '%Y, %m, %d, %H, %M, %S, %f') #phrasing date plain text from config file to next_check_time as a datetime format (UTC time - same time as sever time)

nz_time = next_check_time + datetime.timedelta(hours=13) #converting from UTC time to GMT + 13 (same time as myself)  

def time_break(): #breaks until new_check_time == time now
    while datetime.datetime.utcnow() <= new_check_time: 
        time.sleep(1)



# Search for new feedbacks
def check_new_feedback():

    global new_check_time

    print(msg_time + 'Checking.')

    new_check_time = datetime.datetime.utcnow() + datetime.timedelta(minutes= 1) #update new_check_time to next time to check

    ### Checking feedback code in here (removed) ###

    config_file = open('config.txt', 'r+')
    config_data = config_file.read() 

    mo = next_check_time_regex.sub(r"nextchecktime='" + str(new_check_time.strftime('%Y, %m, %d, %H, %M, %S, %f')) + "'", config_data)

    config_file.seek(0) # Back to line 0 in file
    config_file.write(mo) # writing new_check_time to file so when program closes can remember last check time.

    print(msg_time + 'Completed check and written time to file, next check time = ', new_check_time.strftime('%H:%M'))

    config_file.close() # close config file

    time_break()

    check_new_feedback()


#Starting program here to get into a loop

print('starting \n')
if datetime.datetime.utcnow() <= next_check_time:
    print(msg_time + 'Waiting till %s for next for next check.' % next_check_time.strftime('%H:%M'))
    while datetime.datetime.utcnow() <= next_check_time:
        time.sleep(1)
    check_new_feedback()

else:
    check_new_feedback()

I'm trying to get the msg_time to display the actual time as at the time of the message.

Current result:

starting

00:06 10-06-16 : Waiting till 11:07 for next for next check.
00:06 10-06-16 : Checking.
00:06 10-06-16 : Completed check and written time to file, next check time = 11:08
00:06 10-06-16 : Checking.
00:06 10-06-16 : Completed check and written time to file, next check time = 11:09

Result Wanted:

starting

00:06 10-06-16 : Waiting till 11:07 for next for next check.
00:07 10-06-16 : Checking.
00:07 10-06-16 : Completed check and written time to file, next check time = 11:08
00:08 10-06-16 : Checking.
00:08 10-06-16 : Completed check and written time to file, next check time = 11:09

Blockquote

I have a number of other variables I am also trying to change and call on within the function however they are all showing the original value when being called on (I removed them out of the code for simplicity, as solving the msg_time problem should solve all)

I think the problem might be to do with not exiting the function, but i'm not sure how else to do it.

This is my first program so sorry if its hard to read, any tips will be well appreciated!

Answer 1

Any function referencing msg_time as a global needs to be told that it should use the global version instead of creating a local one. In each function, normally at the top, you should add:

global msg_time

Any future uses will then access / modify the global variable.

Please note that this line:

msg_time = datetime.datetime.now().strftime('%H:%M %d-%M-%y : ')

does not keep msg_time continuously updated, you need to call it every time it's needed to keep your current time up to date.