Confused with 'flags'

[deanhystad]

The term "flags" is used to mean a lot of different things, but I think you are talking about using a variable to signal that something happened. In this context flags are just variables. You can use a flag in an if-else statement, but a flag is not a substitute for else.

found = False  # I have not found a line containing 123
with open('C:/02/somefile.txt','r') as file:
    for line in file:
        if '123' in line: 
            found = True  # I found a line
            break

if found:  # Did I find a line?
    print(line)
    # Do lots of additional processing

A flag is used when there is space between finding and acting on the condition you are interested in. In the example below verbose is a flag used to signal that '--verbose' was contained in the command line arguments.

import sys

verbose = '--verbose' in sys.argv:

with open(sys.args[1], 'r') as file:
    for line in file:
        if verbose:
            print(line)
        if '123' in line: 
            break