Release 20190729: BaseCommand: support for a USAGE_FORMAT usage message format string and a getopt_error_handler method.

Class BaseCommand

A base class for handling nestable command lines.

This class provides the basic parse and dispatch mechanisms for command lines. To implement a command line one instantiates a subclass of BaseCommand:

class MyCommand(BaseCommand):
  GETOPT_SPEC = 'ab:c'
  USAGE_FORMAT = r"""Usage: {cmd} [-a] [-b bvalue] [-c] [--] arguments...
    -a    Do it all.
    -b    But using bvalue.
    -c    The 'c' option!
  """
...
the_cmd = MyCommand()

Running a command is done by:

the_cmd.run(argv)

The subclass is customised by overriding the following methods:

• apply_defaults(options): prepare the initial state of options before any command line options are applied
• apply_opts(options,opts): apply the opts to options. opts is an option value mapping as returned by getopot.getopt.
• cmd_subcmd(argv,options): if the command line options are followed by an argument whose value is subcmd, then method cmd_subcmd(argv,options) will be called where argv contains the command line arguments after subcmd.
• main(argv,options): if there are no command line aguments after the options or the first argument does not have a corresponding cmd_subcmd method then method main(argv,options) will be called where argv contains the command line arguments.
• run_context(argv,options,cmd): a context manager to provide setup or teardown actions to occur before and after the command implementation respectively. If the implementation is a cmd_subcmd method then this is called with cmd=subcmd; if the implementation is main then this is called with cmd=None.

To aid recursive use it is intended that all the per command state is contained in the options object and therefore that in typical use all of apply_opts, cmd_subcmd, main and run_context should be static methods making no reference to self.

Editorial: why not arparse? Primarily because when incorrectly invoked an argparse command line prints the help/usage messgae and aborts the whole programme with SystemExit.

Function docmd(dofunc)

Decorator for Cmd subclass methods to supply some basic quality of service.

This decorator:

• wraps the function call in a cs.pfx.Pfx for context
• intercepts getopt.GetoptErrors, issues a warning and runs self.do_help with the method name, then returns None
• intercepts other Exceptions, issues an exception log message and returns None

The intended use is to decorate cmd.Cmd do_* methods:

from cmd import Cmd
class MyCmd(Cmd):
  @docmd
  def do_something(...):
    ... do something ...

Release Log

Release 20190729: BaseCommand: support for a USAGE_FORMAT usage message format string and a getopt_error_handler method.

Release 20190619.1: Another niggling docstring formatting fix.

Release 20190619: Minor documentation updates.

Release 20190617.2: Lint.

Release 20190617.1: Initial release with @docmd decorator and alpha quality BaseCommand command line assistance class.