Processing command line parameters

Question

This code works, but I'm curious what feedback you have about style and doing things in a more "pythonic" way.

def printUsage():
 print("Usage: goodproxy.py -f <proxyfile> -u <url> -t <timeout>")
def main(argv): 
 filename = ""
 url = ""
 timeout = None
 try:
 # USE GETOPS FOR EASIER PARAMETER PROCESSING
 opts, args = getopt.getopt(argv, "f:u:t:",["file=", "url=", "timeout="])
 except getopt.GetoptError:
 printUsage()
 sys.exit(2)
 # CHECK FOR MISSING PARAMETERS
 # THE 'OPTS' OBJECT CONSISTS OF A LIST OF TUPLES LIKE (PARAM,VAL)
 # LIST COMPREHENSION COLLECTS FIRST ELEMENTS FROM EACH TUPLE INTO A NEW LIST 
 # THEN TESTS THE NEW LIST FOR THE REQUIRED PARAMS 
 if not any(f in [opt[0] for opt in opts] for f in ['-f','--file']):
 printUsage()
 print("Error: -f parameter missing")
 sys.exit(2)
 if not any(u in [opt[0] for opt in opts] for u in ['-u','--url']):
 printUsage()
 print("Error: -u parameter missing")
 sys.exit(2)
 if not any(t in [opt[0] for opt in opts] for t in ['-t','--timeout']):
 printUsage()
 print("Error: -t parameter missing")
 sys.exit(2)
 # CONFIGURE SETTINGS BASED ON THE PASSED IN PARAMETERS
 for opt, arg in opts:
 if opt in ('-f', '--file'):
 print("Using proxies in: " + arg)
 filename = arg
 elif opt in ('-u', '--url'):
 print("Using URL: " + arg)
 url = arg
 elif opt in ('-t', '--timeout'):
 print("Timeout: {0}s".format(arg))
 timeout = arg
if __name__ == "__main__":
 main(sys.argv[1:])

I also found PyLint to assist with improving styling and code smells.

• 200_success: The coolest way I've seen to handle command-line parameters in Python is to use the docopt module.
• shuttle87: Honestly I'd strongly consider going with argparse.
• jacwah: Please don't write comments in ALL CAPS - it looks like you're shouting at us.

Answer 1

First off, I'd suggest that you read PEP8, Python's official style guide, on how to properly style your Python code.

---

Rather than creating a function to print usage, I'd recommend doing something like this instead:

USAGE = "Usage: goodproxy.py -f <proxyfile> -u <url> -t <timeout>"

You can then do this:

print(USAGE)

---

You shouldn't align the equal sign, =, when declaring variables. This means that this:

filename = ""
url = ""
timeout = None

Should be changed to this:

filename = ""
url = ""
timeout = None

Python also has a standard for naming.

1. Variables/function arguments should be in snake_case, and constant variables should be in UPPER_SNAKE_CASE.
2. Functions should be in snake_case as well.
3. Classes should be in PascalCase.

---

Finally, if you plan to do more advanced stuff with command line arguments like this, I'd recommend looking into the argparse library, which comes as a default Python package.

Answer 2

Using argparse, your script can be greatly simplified:

from argparse import ArgumentParser
def main():
 parser = ArgumentParser(description='TODO')
 parser.add_argument('-f', '--file', metavar='PROXYFILE', required=True)
 parser.add_argument('-u', '--url', required=True)
 parser.add_argument('-t', '--timeout', required=True)
 args = parser.parse_args()
 print("Using proxies in: " + args.file)
 print("Using URL: " + args.url)
 print("Timeout: {0}s".format(args.timeout))
if __name__ == "__main__":
 main()

• shuttle87: For a greenfield project I think this is definitely the way to go.