argutils 0.3.3

Installation

$ pip install argutils

Usage example

Let’s say we have a toy program that takes three arguments: a message to print, the number of times to print it, and where to print it. We have two files, an argument spec file we’ll call example_spec.yml, and our program, example.py.

In example_spec.yml:

_meta:
  help: >
    A program that prints a message some number of times to an output
    file
message:
  help: the message to print
  default: "Hello world!"
times:
  help: how many times to print the message
  default: 3
  type: int
output:
  help: where to write the file
  _exclude: True
  default: stdout
  type: File-w
init:
  help: write a config file with default values
  _exclude: True
  argtype: flag

In example.py:

try:
    import ConfigParser
except ImportError:
    import configparser as ConfigParser
import argutils
from argutils import (read, export)

SPEC_FILE = 'example_spec.yml'
CONF_FILE = 'example.cfg'

def main():
    # Used in the config file and argument parser's help
    prog_name = 'example.py'

    config = ConfigParser.SafeConfigParser()

    # Read the spec and build a parser from it
    argsdict = read.from_yaml(open(SPEC_FILE).read())
    parser = export.to_argparser(prog_name, argsdict)

    # If the config file exists and we can read it, use it to set the
    # defaults
    if config.read(CONF_FILE):
        parser = argutils.set_parser_defaults(parser, config)

    args = parser.parse_args()

    if args.init:
        export.to_config_file(prog_name, argsdict, CONF_FILE)

    for _ in range(args.times):
        args.output.write(args.message + '\n')


if __name__ == '__main__':
    main()

Let’s see what we’ve got:

$ python example.py --help
usage: example.py [-h] [--message MESSAGE] [--times TIMES]
                     [--output OUTPUT] [--init]

A program that prints a message some number of times to an output file

optional arguments:
  -h, --help         show this help message and exit
  --message MESSAGE  the message to print
  --times TIMES      how many times to print the message
  --output OUTPUT    where to write the file
  --init             write a config file with default values

We can see that all the arguments we specified in the YAML file are here. Let’s write a config file and check that out:

$ python example.py --init
$ cat example.cfg
## A program that prints a message some number of times to an output file
[example.py]
# the message to print
message = Hello world!
# how many times to print the message
times = 3

Note that two arguments don’t show up here: output and init. These were excluded using the _exclude flag in the YAML file. This is useful for arguments that shouldn’t be set using a config file, including one-time arguments.

Let’s test it:

$ python example.py
Hello world!
Hello world!
Hello world!
$ python example.py --times 1
Hello world!

We can specify the arguments either with command-line flags or by modifying the values in the config file. Values specified on the command line take precedence, followed by the config file values, and resorting to the spec file defaults if nothing else is given.