Question

Here is code from a tutorial in A Byte of Python:

import sys

filename = 'poem.txt'

def readfile(filename):
    #Print a file to standard output
    f = file(filename)
    while True:
        line = f.readline()
        if len(line) == 0:
            break
        print line,
    f.close()

if len(sys.argv) < 2:
    print 'No action specified'
    sys.exit() //<--This is where the error is occurring

if sys.argv[1].startswith('--'):
    option = sys.argv[1][2:] #fetches sys.argv[1] without first 2 char
    if option == 'version':
        print 'Version 1.2'

    elif option == 'help':
        print '''\
This program prints files to the standard output.
Any number of files can be specified.
Options include:
    --version: Prints the version number
    --help: Displays this help'''

    else:
        print 'Unknown option'
    sys.exit()

else:
    for filename in sys.argv[1:]:
        readfile(filename)

When I run this code, this is the error that appears:

Traceback (most recent call last):
  File "C:/Python/sysmodulepr.py", line 17, in <module>
    sys.exit()
SystemExit

I don’t understand why. Please help.

Answer 1

It’s telling you that sys.exit() has executed on line 17 of your program.

The entry for for sys.exit in the Python documentation tells you that this exits your program.

There’s no way this line can execute without producing other output, so I think there’s something missing in the question.