optspec - A wrapper around getopt

optspec is a wrapper around getopt that provides option parsing, mapping, counting, and enforcement of required parameters. I wrote this because I enjoy the simplicity of getopt.getopt(), but dislike the duplication involved in interpreting its results into variables or settings.

Change Log

May 1 2016 (v0.5): Added ability to pass arbitrary parameters into SubcommandMap.invoke().

Option Specifications: The Option.opt() Function

The opt() function accepts a series of option forms, and keyword arguments identifying the option's behavior.

The option forms are either shortopts or longopts based on their length: single-char forms are shortopts and multi character forms are longopts (sorry, no single-char longopts). Every form in the specification (optspec) will map to the same key in the resulting option map (optmap). This key, aka name, is determined by the first longopt specified, or the first shortopt specified if no longopts are specified, and can also explicitly be specified with the name keyword argument.

• name: Explicitly specifies the option map value key, which is normally implied from the option forms. This can also be used to map options with different meanings to the same value key, as per the -v and -q options in the example below.
• param = True: Indicates that the option takes a parameter. If the option is not specified, the value in the resulting optmap will be determined based on the following rules: - If default was specified, that value is provided. - If multi = True, the result is an empty list to indicate that no parameters were provided for a multi parameter option. - Otherwise, None is provided as the value for the optmap key.
• required = True: Indicates that the option is required, and implies param = True. If the option is not specified in sys.argv or the provided argv, the parse() function will raise an exception.
• additive = True: Indicates that the option is additive. If the option takes a parameter, then each time the parameter is provided, it is added to the previous value instead of replacing it using the + operator. If the option takes no parameters, then increment is added to default (or 0 if default was not provided).
• multi = True: Indicates that the option can take multiple parameters by being specified multiple times. Each time the option is specified the resulting value is added to a list and this list is provided as the value for the optmap key. Note that an option may not be additive and multi, if multi is specified all rules for additive are ignored.
• default: Specifies a default value to use for an option with parameters, and also indicates the starting value for additive options. If specified for an option that is multi, this had ought to be a list or collection of some sort.
• parser: Provide a function that is used to parse parameters to options from strings. This is the identify function lambda a: a by default. Some common useful values for this include int and float.
• increment: Specifies the value to be added to default for additive options where param = False. This defaults to 1.

Example Usage

To use optspec, create an Option object, then specify a series of options using the opt() function successively. Then, you may call the parse() function with no parameters to parse from sys.argv implicitly, or provide your own argv as a parameter.:

from optspec import Options

optmap, args = ( Options()
     .opt('s', 'safe')
     .opt('i', 'input', required = True)
     .opt('o', 'output', param = True, default = 'a.out')
     .opt('v', 'verbose', additive = True)
     .opt('p', 'ports', multi = True, parser = int)
     .opt('c', 'count', param = True, additive = True, parser = int, default = 0)
     .opt('q', 'quiet', name = 'verbose', additive = True, increment = -1)
     .parse() )

print('optmap = %s' % repr(optmap))
print('args = %s' % repr(args))

$ python test.py --input a -qq -p 1 -p 2 -c -10000 -c 400 Hello Python
     optmap = {'output': 'a.out', 'count': -9600, 'safe': False, 'ports': [1, 2], 'input': 'a', 'verbose': -2}
     args = ['Hello', 'Python']

Mapping Functions to Subcommands: The SubcommandMap Object

Version 0.4 brings the SubcommandMap object, which provides pretty semantics to mapping functions to subcommands, and declaring which subcommand is the default. It is common to write tools with subcommands, where the first element in argv after the program name indicates a subcommand. Examples are tools like 'git', which have many subcommands.

SubcommandMap allows you to declare an instance, and then use decorators to wrap your functions and place them in a logical mapping from subcommand to function. The function will receive all of argv as arguments, minus the first element if it is the name of a known subcommand.

Example Usage

In this example, our command supports two subcommands, with one of them being default.:

from optspec import SubcommandMap

subcom = SubcommandMap()

@subcom.define('polite', default = True)
def polite_version(argv):
   if len(argv) < 2:
      print("I'm sorry, I don't know who you are.")

   else:
      print("Good morning, %s!  What a lovely day!" % argv[1])

@subcom.define('rude')
def rude_version(argv):
   if len(argv) < 2:
      print("Who the hell are you?")

   else:
      print("%s??  What a stupid name!" % argv[1])

if __name__ == "__main__":
   subcom.invoke()

$ python subcom-test.py
I'm sorry, I don't know who you are.
$ python subcom-test.py Lain
Good morning, Lain!  What a lovely day!
$ python subcom-test.py rude
Who the hell are you?
$ python subcom-test.py rude Lain
Lain??  What a stupid name!