Python: Essential Reference, Third Edition

Reading Options and Environment Variables

When the interpreter starts, command-line options are placed in the list sys.argv. The first element is the name of the program. Subsequent elements are the options presented on the command line after the program name. The following program shows how to access command-line options:

# printopt.py
# Print all of the command-line options
import sys
for i in range(len(sys.argv)):
    print "sys.argv[%d] = %s" % (i, sys.argv[i])

Running the program produces the following:

% python printopt.py foo bar -p
sys.argv[0] = printopt.py
sys.argv[1] = foo
sys.argv[2] = bar
sys.argv[3] = -p
%

Environment variables are accessed in the dictionary os.environ. For example:

 import os path = os.environ["PATH"] user = os.environ["USER"] ...