Skip to main content

simpleopt - a simple parser for options in command line

Project description

Usage Example

You just define a function, and optionally annotate the type of the parameters, the same arguments will be parsed on the command line:

@annotation(command=str, interval=float, differences=bool,
            args=str, kwargs=str)
def watch(command, interval=2.0, differences=False, *args, **kwargs):
    print (command, interval, differences, args, kwargs)

if __name__ == '__main__':

Then you can call it like this, supposing you saved it on a file named and made it executable:

$ "df -h"
('df -h', 2.0, False, (), {})

$ --interval 1.0 "df -h"
('df -h', 1.0, False, (), {})

$ --noverbose --differences "df -h"
('df -h', 1.0, True, (), {})

$ python --foo bar --bar baz "df -h" quux quuux
('df -h', 2.0, False, ('quux', 'quuux'), {'foo': 'bar', 'bar': 'baz'})

Another example:

def example(foo):
    return foo

$ --foo a:1,b:2,c:3
{'a': 1, 'c': 3, 'b': 2}

$ a:1,b:2,c:3
{'a': 1, 'c': 3, 'b': 2}

Working details

The command-line arguments are classified in one of two types: (i) option arguments and (ii) positional arguments.

  1. option arguments have the form –OPTION or –OPTION=VALUE where OPTION is the argument name and VALUE is an optional value given to that argument.

  2. positional arguments are those that are not option arguments.

The way that command-line arguments are assigned to the function’s formal parameters differ from the way that python assigns input arguments in python code.

When a python script is run on the command line, the command-line arguments are assigned to the function’s formal parameters as follows:

  • For each formal parameter, there is a slot which will be used to contain the value of the argument assigned to that parameter.

  • Each slot is either ‘empty’ or ‘filled’. Slots which had values assigned to them are ‘filled’, otherwise they are ‘empty’.

  • Initially, all slots are marked ‘empty’.

  • Option arguments are assigned first, followed by positional arguments.

  • For each option argument:

    o If there is a parameter with the same name as the option argument, then

    the argument value is assigned to that parameter slot. However, if the parameter is already filled, then that is an error.

    o Otherwise, if there is a ‘keyword dictionary’ argument, the argument is

    added to the dictionary using the keyword name as the dictionary key, unless there is already an entry with that key, in which case it is an error.

    o Otherwise, if there is no keyword dictionary, and no matching named

    parameter, then it is an error.

  • For each positional argument:

    o Attempt to bind the argument to the first unfilled parameter slot that

    has no default value. If the slot is not a vararg slot, then mark the slot as ‘filled’.

    o Otherwise, if the next unfilled slot is a vararg slot then all remaining

    positional arguments are placed into the vararg slot.

  • Finally:

    o If the vararg slot is not yet filled, assign an empty tuple as its


    o If the keyword dictionary argument is not yet filled, assign an empty

    dicionary as its value.

    o For each remaining empty slot: if there is a default value for that

    slot, then fill the slot with the default value. If there is no default value, then it is an error.

When an error happens, a message is printed about the error.

Project details

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distribution

simpleopt-0.1.1a.tar.gz (10.1 kB view hashes)

Uploaded Source

Supported by

AWS AWS Cloud computing and Security Sponsor Datadog Datadog Monitoring Fastly Fastly CDN Google Google Download Analytics Microsoft Microsoft PSF Sponsor Pingdom Pingdom Monitoring Sentry Sentry Error logging StatusPage StatusPage Status page