cs-cmdutils 20200521

convenience functions for working with the Cmd module and other command line related stuff

Convenience functions for working with the Cmd module and other command line related stuff.

Latest release 20200521:

• BaseCommand.run: support using BaseCommand subclasses as cmd_* names to make it easy to nest BaseCommands.
• BaseCommand: new hack_postopts_argv method called after parsing the main command line options, for inferring subcommands or the like.
• BaseCommand: extract "Usage:" paragraphs from subcommand method docstrings to build the main usage message.
• BaseCommand: new cmd_help default command.
• Assorted bugfixes and small improvements.

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) sequence as returned by getopot.getopt.
• cmd_subcmd(argv,options): if the command line options are followed by an argument whose value is subcmd, then the 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 20200521:

• BaseCommand.run: support using BaseCommand subclasses as cmd_* names to make it easy to nest BaseCommands.
• BaseCommand: new hack_postopts_argv method called after parsing the main command line options, for inferring subcommands or the like.
• BaseCommand: extract "Usage:" paragraphs from subcommand method docstrings to build the main usage message.
• BaseCommand: new cmd_help default command.
• Assorted bugfixes and small improvements.

Release 20200318:

• BaseCommand.run: make argv optional, get additional usage keywords from self.USAGE_KEYWORDS.
• @BaseCommand.add_usage_to_docstring: honour cls.USAGE_KEYWORDS.
• BaseCommand: do not require GETOPT_SPEC for commands with no defined options.
• BaseCommand.run: call cs.logutils.setup_logging.

Release 20200229: Improve subcommand selection logic, replace StackableValues with stackattrs, drop cmd from arguments passed to main/cmd_* methods (present in options).

Release 20200210:

• New BaseCommand.add_usage_to_docstring class method to be called after class setup, to append the usage message to the class docstring.
• BaseCommand.run: remove spurious Pfx(cmd), as logutils does this for us already.

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.