A very simple argument parser

Scripting •

I’m a guy who usually writes a lot of script files to automate my daily routine. To extend the flexibility of the script, a good piece of advice is to make the script accepts parameters passing from command.

There are tons of argument parser libraries out there, for every programming language we can imagine. It’s because the command-line application is mostly the 1st class resident of a programming language. I haven’t checked all of the libraries or dug deeply into a specific library (yes, I’m a lazy guy, too). I sometimes intended to apply some of the libraries for this purpose for my Python scripts (for example argparse). However, I feel they are too complex for a lazy guy like me, and all of the time, I give up adopting a library and use raw argument array received from the environment instead (ie. sys.argv in Python).

After giving up too many times, I just figure out that I could make a simple one with very simple approaches:

  1. An argument parser parses the array of params only.
  2. Supports getting an argument with position or with key for key-value.
  3. Checks whether a key exists.

No more, no less!

The result of all of these approaches is this 14-LOC Python script:

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class ArgumentParser:
    def __init__(self, args):
        self.positioned_arguments = list(filter(lambda x: not x.startswith('--'), args))
        self.named_argument_map = dict(map(lambda x: x.split("=", 1) if "=" in x else (x, None),
                                           filter(lambda x: x.startswith('--'), args)))

    def get(self, key_or_index):
        if type(key_or_index) is int:
            return self.positioned_arguments[key_or_index]
        else:
            return self.named_argument_map[str(key_or_index)]

    def has_key(self, key):
        return key in self.named_argument_map

Just a note: positioned_arguments doesn’t count key-value pair arguments. Key-value arguments can be seen as optional parameters.

Conclusion

Do you need a long tutorial before starting using this parser?