Check and wait until a file exists to read it

Question

I need to wait until a file is created then read it in. I have the below code, but sure it does not work:

import os.path
if os.path.isfile(file_path):
    read file in
else:
    wait

Any ideas please?

Answer 1

A simple implementation could be:

import os.path
import time

while not os.path.exists(file_path):
    time.sleep(1)

if os.path.isfile(file_path):
    # read file
else:
    raise ValueError("%s isn't a file!" % file_path)

You wait a certain amount of time after each check, and then read the file when the path exists. The script can be stopped with the KeyboardInterruption exception if the file is never created. You should also check if the path is a file after, to avoid some unwanted exceptions.

Answer 2

The following script will break as soon as the file is dowloaded or the file_path is created otherwise it will wait upto 10 seconds for the file to be downloaded or the file_path to be created before breaking.

import os
import time

time_to_wait = 10
time_counter = 0
while not os.path.exists(file_path):
    time.sleep(1)
    time_counter += 1
    if time_counter > time_to_wait:break

print("done")