[TIPS] Python Argument Parser - Bad Practices
By khoanc, at: Oct. 18, 2024, 11:28 a.m.
![[TIPS] Python Argument Parser - Bad Practices](/media/filer_public_thumbnails/filer_public/53/22/532205b4-0a89-4637-9f86-e7d316454d2b/python_argument_parsers_issues.png__1500x900_crop_subsampling-2_upscale.png)
![[TIPS] Python Argument Parser - Bad Practices](/media/filer_public_thumbnails/filer_public/53/22/532205b4-0a89-4637-9f86-e7d316454d2b/python_argument_parsers_issues.png__400x240_crop_subsampling-2_upscale.png)
Bad Practices When Passing Arguments in Python Scripts
1. Using sys.argv Directly
import sys
def main():
if len(sys.argv) < 3:
print("Not enough arguments!")
return
arg1 = sys.argv[1]
arg2 = sys.argv[2]
if arg1 == 'option1':
print(f"Option 1 selected with value {arg2}")
elif arg1 == 'option2':
print(f"Option 2 selected with value {arg2}")
else:
print("Unknown option!")
if __name__ == "__main__":
main()
Bad Practice: Directly using sys.argv for parsing arguments can be error-prone and difficult to maintain.
Fix: Use the argparse module for parsing arguments. It provides a more robust and user-friendly way to handle command-line arguments.
import argparse
def main():
parser = argparse.ArgumentParser(description="A sample argument parser.")
parser.add_argument('arg1', type=str, help="First argument")
parser.add_argument('arg2', type=str, help="Second argument")
args = parser.parse_args()
if args.arg1 == 'option1':
print(f"Option 1 selected with value {args.arg2}")
elif args.arg1 == 'option2':
print(f"Option 2 selected with value {args.arg2}")
else:
print("Unknown option!")
if __name__ == "__main__":
main()
2. No Usage or Help Message
import sys
def main():
if len(sys.argv) < 3:
print("Not enough arguments!")
return
arg1 = sys.argv[1]
arg2 = sys.argv[2]
if arg1 == 'option1':
print(f"Option 1 selected with value {arg2}")
elif arg1 == 'option2':
print(f"Option 2 selected with value {arg2}")
else:
print("Unknown option!")
if __name__ == "__main__":
main()
Bad Practice: Not providing a usage or help message makes it difficult for users to understand how to use the script.
Fix: Use the argparse module, which automatically provides help and usage messages.
import argparse
def main():
parser = argparse.ArgumentParser(description="A sample argument parser.")
parser.add_argument('arg1', type=str, help="First argument")
parser.add_argument('arg2', type=str, help="Second argument")
args = parser.parse_args()
if args.arg1 == 'option1':
print(f"Option 1 selected with value {args.arg2}")
elif args.arg1 == 'option2':
print(f"Option 2 selected with value {args.arg2}")
else:
print("Unknown option!")
if __name__ == "__main__":
main()
No Validation of Arguments
import sys
def main():
if len(sys.argv) < 3:
print("Not enough arguments!")
return
arg1 = sys.argv[1]
arg2 = sys.argv[2]
if arg1 == 'option1':
print(f"Option 1 selected with value {arg2}")
elif arg1 == 'option2':
print(f"Option 2 selected with value {arg2}")
else:
print("Unknown option!")
if __name__ == "__main__":
main()
Bad Practice: Not validating arguments can lead to runtime errors or unexpected behavior.
Fix: Use argparse to specify the type of arguments and validate them accordingly.
import argparse
def main():
parser = argparse.ArgumentParser(description="A sample argument parser.")
parser.add_argument('arg1', type=str, choices=['option1', 'option2'], help="First argument")
parser.add_argument('arg2', type=str, help="Second argument")
args = parser.parse_args()
if args.arg1 == 'option1':
print(f"Option 1 selected with value {args.arg2}")
elif args.arg1 == 'option2':
print(f"Option 2 selected with value {args.arg2}")
if __name__ == "__main__":
main()
Ignoring Edge Cases
import sys
def main():
if len(sys.argv) < 3:
print("Not enough arguments!")
return
arg1 = sys.argv[1]
arg2 = sys.argv[2]
if arg1 == 'option1':
print(f"Option 1 selected with value {arg2}")
elif arg1 == 'option2':
print(f"Option 2 selected with value {arg2}")
else:
print("Unknown option!")
if __name__ == "__main__":
main()
Bad Practice: Not handling edge cases like missing arguments, incorrect data types, or invalid values.
Fix: Use argparse features like default values, type checking, and required arguments to handle edge cases.
import argparse
def main():
parser = argparse.ArgumentParser(description="A sample argument parser.")
parser.add_argument('arg1', type=str, choices=['option1', 'option2'], help="First argument")
parser.add_argument('arg2', type=str, help="Second argument")
parser.add_argument('--optional', type=int, default=0, help="An optional argument")
args = parser.parse_args()
if args.arg1 == 'option1':
print(f"Option 1 selected with value {args.arg2} and optional {args.optional}")
elif args.arg1 == 'option2':
print(f"Option 2 selected with value {args.arg2} and optional {args.optional}")
if __name__ == "__main__":
main()
Poor Argument Naming
import sys
def main():
if len(sys.argv) < 3:
print("Not enough arguments!")
return
arg1 = sys.argv[1]
arg2 = sys.argv[2]
if arg1 == 'option1':
print(f"Option 1 selected with value {arg2}")
elif arg1 == 'option2':
print(f"Option 2 selected with value {arg2}")
else:
print("Unknown option!")
if __name__ == "__main__":
main()
Bad Practice: Using non-descriptive or ambiguous argument names can confuse users.
Fix: Use clear and descriptive argument names that convey their purpose.
import argparse
def main():
parser = argparse.ArgumentParser(description="A sample argument parser.")
parser.add_argument('command', type=str, choices=['start', 'stop'], help="Command to execute")
parser.add_argument('value', type=str, help="Value associated with the command")
args = parser.parse_args()
if args.command == 'start':
print(f"Starting with value {args.value}")
elif args.command == 'stop':
print(f"Stopping with value {args.value}")
if __name__ == "__main__":
main()
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