Metadata-Version: 2.1
Name: cs.cmdutils
Version: 20240412
Summary: Convenience functions for working with the Cmd module, the BaseCommand class for constructing command line programmes, and other command line related stuff.
Author-email: Cameron Simpson <cs@cskk.id.au>
License: GNU General Public License v3 or later (GPLv3+)
Project-URL: URL, https://bitbucket.org/cameron_simpson/css/commits/all
Keywords: python2,python3
Platform: UNKNOWN
Classifier: Programming Language :: Python
Classifier: Programming Language :: Python :: 3
Classifier: Development Status :: 4 - Beta
Classifier: Intended Audience :: Developers
Classifier: Operating System :: OS Independent
Classifier: Topic :: Software Development :: Libraries :: Python Modules
Classifier: License :: OSI Approved :: GNU General Public License v3 or later (GPLv3+)
Description-Content-Type: text/markdown

Convenience functions for working with the Cmd module,
the BaseCommand class for constructing command line programmes,
and other command line related stuff.

*Latest release 20240412*:
* BaseCommand.run_context: do not store .upd and .runstate on the options (it confuses options in subcommands and we have @uses_runstate and @uses_upd forthis anyway these days).
* BaseCommand.run_context: catch SIGQUIT, present the default handler as BaseCommand.handle_signal.

## 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!
        """
        ...

and provides either a `main` method if the command has no subcommands
or a suite of `cmd_`*subcommand* methods, one per subcommand.

Running a command is done by:

    MyCommand(argv).run()

Modules which implement a command line mode generally look like this:

    ... imports etc ...
    def main(argv=None, **run_kw):
        """ The command line mode.
        """
        return MyCommand(argv).run(**run_kw)
    ... other code ...
    class MyCommand(BaseCommand):
    ... other code ...
    if __name__ == '__main__':
        sys.exit(main(sys.argv))

Instances have a `self.options` attribute on which optional
modes are set,
avoiding conflict with the attributes of `self`.

Subclasses with no subcommands
generally just implement a `main(argv)` method.

Subclasses with subcommands
should implement a `cmd_`*subcommand*`(argv)` instance method
for each subcommand.
If a subcommand is itself implemented using `BaseCommand`
then it can be a simple attribute:

    cmd_subthing = SubThingCommand

Returning to methods, if there is a paragraph in the method docstring
commencing with `Usage:`
then that paragraph is incorporated automatically
into the main usage message.
Example:

    def cmd_ls(self, argv):
        """ Usage: {cmd} [paths...]
              Emit a listing for the named paths.

            Further docstring non-usage information here.
        """
        ... do the "ls" subcommand ...

The subclass is customised by overriding the following methods:
* `apply_opt(opt,val)`:
  apply an individual getopt global command line option
  to `self.options`.
* `apply_opts(opts)`:
  apply the `opts` to `self.options`.
  `opts` is an `(option,value)` sequence
  as returned by `getopot.getopt`.
  The default implementation iterates over these and calls `apply_opt`.
* `cmd_`*subcmd*`(argv)`:
  if the command line options are followed by an argument
  whose value is *subcmd*,
  then the method `cmd_`*subcmd*`(subcmd_argv)`
  will be called where `subcmd_argv` contains the command line arguments
  following *subcmd*.
* `main(argv)`:
  if there are no command line arguments after the options
  or the first argument does not have a corresponding
  `cmd_`*subcmd* method
  then method `main(argv)`
  will be called where `argv` contains the command line arguments.
* `run_context()`:
  a context manager to provide setup or teardown actions
  to occur before and after the command implementation respectively,
  such as to open and close a database.

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`.
But also, I find the whole argparse `add_argument` thing cumbersome.

*Method `BaseCommand.__init__(self, argv=None, *, cmd=None, options=None, **kw_options)`*:
Initialise the command line.
Raises `GetoptError` for unrecognised options.

Parameters:
* `argv`:
  optional command line arguments
  including the main command name if `cmd` is not specified.
  The default is `sys.argv`.
  The contents of `argv` are copied,
  permitting desctructive parsing of `argv`.
* `cmd`:
  optional keyword specifying the command name for context;
  if this is not specified it is taken from `argv.pop(0)`.
* `options`:
  an optional keyword providing object for command state and context.
  If not specified a new `self.Options` instance
  is allocated for use as `options`.
  The default `Options` class is `BaseCommandOptions`,
  a dataclass with some prefilled attributes and properties
  to aid use later.
Other keyword arguments are applied to `self.options`
as attributes.

The `cmd` and `argv` parameters have some fiddly semantics for convenience.
There are 3 basic ways to initialise:
* `BaseCommand()`: `argv` comes from `sys.argv`
  and the value for `cmd` is derived from `argv[0]`
* `BaseCommand(argv)`: `argv` is the complete command line
  including the command name and the value for `cmd` is
  derived from `argv[0]`
* `BaseCommand(argv, cmd=foo)`: `argv` is the command
  arguments _after_ the command name and `cmd` is set to
  `foo`

The command line arguments are parsed according to
the optional `GETOPT_SPEC` class attribute (default `''`).
If `getopt_spec` is not empty
then `apply_opts(opts)` is called
to apply the supplied options to the state
where `opts` is the return from `getopt.getopt(argv,getopt_spec)`.

After the option parse,
if the first command line argument *foo*
has a corresponding method `cmd_`*foo*
then that argument is removed from the start of `argv`
and `self.cmd_`*foo*`(argv,options,cmd=`*foo*`)` is called
and its value returned.
Otherwise `self.main(argv,options)` is called
and its value returned.

If the command implementation requires some setup or teardown
then this may be provided by the `run_context`
context manager method,
called with `cmd=`*subcmd* for subcommands
and with `cmd=None` for `main`.

*`BaseCommand.Options`*

*Method `BaseCommand.__init_subclass__()`*:
Update subclasses of `BaseCommand`.

Appends the usage message to the class docstring.

*Method `BaseCommand.apply_opt(self, opt, val)`*:
Handle an individual global command line option.

This default implementation raises a `RuntimeError`.
It only fires if `getopt` actually gathered arguments
and would imply that a `GETOPT_SPEC` was supplied
without an `apply_opt` or `apply_opts` method to implement the options.

*Method `BaseCommand.apply_opts(self, opts)`*:
Apply command line options.

Subclasses can override this
but it is usually easier to override `apply_opt(opt,val)`.

*Method `BaseCommand.apply_preargv(self, argv)`*:
Do any preparsing of `argv` before the subcommand/main-args.
Return the remaining arguments.

This default implementation returns `argv` unchanged.

*Method `BaseCommand.cmd_help(argv)`*:
Usage: {cmd} [-l] [subcommand-names...]
Print help for subcommands.
This outputs the full help for the named subcommands,
or the short help for all subcommands if no names are specified.
-l  Long help even if no subcommand-names provided.

*Method `BaseCommand.cmd_shell(self, argv)`*:
Usage: {cmd}
Run a command prompt via cmd.Cmd using this command's subcommands.

*Method `BaseCommand.cmdloop(intro=None)`*:
Use `cmd.Cmd` to run a command loop which calls the `cmd_`* methods.

*Method `BaseCommand.getopt_error_handler(cmd, options, e, usage, subcmd=None)`*:
The `getopt_error_handler` method
is used to control the handling of `GetoptError`s raised
during the command line parse
or during the `main` or `cmd_`*subcmd*` calls.

This default handler issues a warning containing the exception text,
prints the usage message to standard error,
and returns `True` to indicate that the error has been handled.

The handler is called with these parameters:
* `cmd`: the command name
* `options`: the `options` object
* `e`: the `GetoptError` exception
* `usage`: the command usage or `None` if this was not provided
* `subcmd`: optional subcommand name;
  if not `None`, is the name of the subcommand which caused the error

It returns a true value if the exception is considered handled,
in which case the main `run` method returns 2.
It returns a false value if the exception is considered unhandled,
in which case the main `run` method reraises the `GetoptError`.

To let the exceptions out unhandled
this can be overridden with a method which just returns `False`.

Otherwise,
the handler may perform any suitable action
and return `True` to contain the exception
or `False` to cause the exception to be reraised.

*Method `BaseCommand.handle_signal(self, sig, frame, *, runstate: Optional[cs.resources.RunState] = <function <lambda> at 0x10d5b1d80>)`*:
The default signal handler, which cancels the default `RunState`.

*Method `BaseCommand.poparg(argv: List[str], *a, unpop_on_error=False)`*:
Pop the leading argument off `argv` and parse it.
Return the parsed argument.
Raises `getopt.GetoptError` on a missing or invalid argument.

This is expected to be used inside a `main` or `cmd_*`
command handler method or inside `apply_preargv`.

You can just use:

    value = argv.pop(0)

but this method provides conversion and valuation
and a richer failure mode.

Parameters:
* `argv`: the argument list, which is modified in place with `argv.pop(0)`
* the argument list `argv` may be followed by some help text
  and/or an argument parser function.
* `validate`: an optional function to validate the parsed value;
  this should return a true value if valid,
  or return a false value or raise a `ValueError` if invalid
* `unvalidated_message`: an optional message after `validate`
  for values failing the validation
* `unpop_on_error`: optional keyword parameter, default `False`;
  if true then push the argument back onto the front of `argv`
  if it fails to parse; `GetoptError` is still raised

Typical use inside a `main` or `cmd_*` method might look like:

    self.options.word = self.poparg(argv, int, "a count value")
    self.options.word = self.poparg(
        argv, int, "a count value",
       lambda count: count > 0, "count should be positive")

Because it raises `GetoptError` on a bad argument
the normal usage message failure mode follows automatically.

Demonstration:

    >>> argv = ['word', '3', 'nine', '4']
    >>> BaseCommand.poparg(argv, "word to process")
    'word'
    >>> BaseCommand.poparg(argv, int, "count value")
    3
    >>> BaseCommand.poparg(argv, float, "length")
    Traceback (most recent call last):
      ...
    getopt.GetoptError: length 'nine': float('nine'): could not convert string to float: 'nine'
    >>> BaseCommand.poparg(argv, float, "width", lambda width: width > 5)
    Traceback (most recent call last):
      ...
    getopt.GetoptError: width '4': invalid value
    >>> BaseCommand.poparg(argv, float, "length")
    Traceback (most recent call last):
      ...
    getopt.GetoptError: length: missing argument
    >>> argv = ['-5', 'zz']
    >>> BaseCommand.poparg(argv, float, "size", lambda f: f>0, "size should be >0")
    Traceback (most recent call last):
      ...
    getopt.GetoptError: size '-5': size should be >0
    >>> argv  # -5 was still consumed
    ['zz']
    >>> BaseCommand.poparg(argv, float, "size2", unpop_on_error=True)
    Traceback (most recent call last):
      ...
    getopt.GetoptError: size2 'zz': float('zz'): could not convert string to float: 'zz'
    >>> argv  # zz was pushed back
    ['zz']

*Method `BaseCommand.popopts(argv, attrfor=None, **opt_specs)`*:
Parse option switches from `argv`, a list of command line strings
with leading option switches.
Modify `argv` in place and return a dict mapping switch names to values.

The optional positional argument `attrfor`
may supply an object whose attributes may be set by the options,
for example:

    def cmd_foo(self, argv):
        self.popopts(argv, self.options, a='all', j_=('jobs', int))
        ... use self.options.jobs etc ...

The expected options are specified by the keyword parameters
in `opt_specs`:
* options not starting with a letter may be preceeded by an underscore
  to allow use in the parameter list, for example `_1='once'`
  for a `-1` option setting the `once` option name
* a single letter name specifies a short option
  and a multiletter name specifies a long option
* options requiring an argument have a trailing underscore
* options not requiring an argument normally imply a value
  of `True`; if their synonym commences with a dash they will
  imply a value of `False`, for example `n='dry_run',y='-dry_run'`

As it happens, the `BaseCommandOptions` class provided a `popopts` method
which is a shim for this method with `attrfor=self` i.e. the options object.
So common use in a command method might look like this:

    class SomeCommand(BaseCommand):

        def cmd_foo(self, argv):
            options = self.options
            # accept a -j or --jobs options
            options.poopts(argv, jobs=1, j='jobs')
            print("jobs =", options.jobs)

Example:

    >>> import os.path
    >>> options = SimpleNamespace(
    ...   all=False,
    ...   jobs=1,
    ...   number=0,
    ...   once=False,
    ...   path=None,
    ...   trace_exec=True,
    ...   verbose=False,
    ...   dry_run=False)
    >>> argv = ['-1', '-v', '-y', '-j4', '--path=/foo', 'bah', '-x']
    >>> opt_dict = BaseCommand.popopts(
    ...   argv,
    ...   options,
    ...   _1='once',
    ...   a='all',
    ...   j_=('jobs',int),
    ...   n='dry_run',
    ...   v='verbose',
    ...   x='-trace_exec',
    ...   y='-dry_run',
    ...   dry_run=None,
    ...   path_=(str, os.path.isabs, 'not an absolute path'),
    ...   verbose=None,
    ... )
    >>> opt_dict
    {'once': True, 'verbose': True, 'dry_run': False, 'jobs': 4, 'path': '/foo'}
    >>> options
    namespace(all=False, jobs=4, number=0, once=True, path='/foo', trace_exec=True, verbose=True, dry_run=False)

*Method `BaseCommand.repl(self, *argv, banner=None, local=None)`*:
Run an interactive Python prompt with some predefined local names.
Aka REPL (Read Evaluate Print Loop).

Parameters:
* `argv`: any notional command line arguments
* `banner`: optional banner string
* `local`: optional local names mapping

The default `local` mapping is a `dict` containing:
* `argv`: from `argv`
* `options`: from `self.options`
* `self`: from `self`
* the attributes of `options`
* the attributes of `self`

This is not presented automatically as a subcommand, but
commands wishing such a command should provide something
like this:

    def cmd_repl(self, argv):
        """ Usage: {cmd}
              Run an interactive Python prompt with some predefined local names.
        """
        return self.repl(*argv)

*Method `BaseCommand.run(self, **kw_options)`*:
Run a command.
Returns the exit status of the command.
May raise `GetoptError` from subcommands.

Any keyword arguments are used to override `self.options` attributes
for the duration of the run,
for example to presupply a shared `Upd` from an outer context.

If the first command line argument *foo*
has a corresponding method `cmd_`*foo*
then that argument is removed from the start of `argv`
and `self.cmd_`*foo*`(cmd=`*foo*`)` is called
and its value returned.
Otherwise `self.main(argv)` is called
and its value returned.

If the command implementation requires some setup or teardown
then this may be provided by the `run_context()`
context manager method.

*Method `BaseCommand.run_context(*a, upd: Optional[cs.upd.Upd] = <function uses_upd.<locals>.<lambda> at 0x10d48e290>, **kw)`*:
The context manager which surrounds `main` or `cmd_`*subcmd*.

This default does several things, and subclasses should
override it like this:

    @contextmanager
    def run_context(self):
      with super().run_context():
        try:
          ... subclass context setup ...
            yield
        finally:
          ... any unconditional cleanup ...

*Method `BaseCommand.subcommand_usage_text(subcmd, usage_format_mapping=None, short=False)`*:
Return the usage text for a subcommand.

Parameters:
* `subcmd`: the subcommand name
* `short`: just include the first line of the usage message,
  intented for when there are many subcommands

*Method `BaseCommand.subcommands()`*:
Return a mapping of subcommand names to subcommand specifications
for class attributes which commence with `cls.SUBCOMMAND_METHOD_PREFIX`
by default `'cmd_'`.

*Method `BaseCommand.usage_text(*, cmd=None, format_mapping=None, subcmd=None, short=False)`*:
Compute the "Usage:" message for this class
from the top level `USAGE_FORMAT`
and the `'Usage:'`-containing docstrings of its `cmd_*` methods.

Parameters:
* `cmd`: optional command name, default derived from the class name
* `format_mapping`: an optional format mapping for filling
  in format strings in the usage text
* `subcmd`: constrain the usage to a particular subcommand named `subcmd`;
  this is used to produce a shorter usage for subcommand usage failures

## Class `BaseCommandCmd(cmd.Cmd)`

A `cmd.Cmd` subclass used to provide interactive use of a
command's subcommands.

The `BaseCommand.cmdloop()` class method instantiates an
instance of this cand calls its `.cmdloop()` method
i.e. `cmd.Cmd.cmdloop`.

## Class `BaseCommandOptions(cs.threads.HasThreadState)`

A base class for the `BaseCommand` `options` object.

This is the default class for the `self.options` object
available during `BaseCommand.run()`,
and available as the `BaseCommand.Options` attribute.

Any keyword arguments are applied as field updates to the instance.

It comes prefilled with:
* `.dry_run=False`
* `.force=False`
* `.quiet=False`
* `.verbose=False`
and a `.doit` property which is the inverse of `.dry_run`.

It is recommended that if ``BaseCommand` subclasses use a
different type for their `Options` that it should be a
subclass of `BaseCommandOptions`.
Since `BaseCommandOptions` is a data class, this typically looks like:

    @dataclass
    class Options(BaseCommand.Options):
        ... optional extra fields etc ...

*Method `BaseCommandOptions.__call__(self, **updates)`*:
Calling the options object returns a context manager whose
value is a copy of the options with any `suboptions` applied.

Example showing the semantics:

    >>> from cs.cmdutils import BaseCommandOptions
    >>> options = BaseCommandOptions(x=1)
    >>> assert options.x == 1
    >>> assert not options.verbose
    >>> with options(verbose=True) as subopts:
    ...     assert options is not subopts
    ...     assert options.x == 1
    ...     assert not options.verbose
    ...     assert subopts.x == 1
    ...     assert subopts.verbose
    ...
    >>> assert options.x == 1
    >>> assert not options.verbose

*Method `BaseCommandOptions.copy(self, **updates)`*:
Return a new instance of `BaseCommandOptions` (well, `type(self)`)
which is a shallow copy of the public attributes from `self.__dict__`.

Any keyword arguments are applied as attribute updates to the copy.

*Property `BaseCommandOptions.doit`*:
I usually use a `doit` flag,
the inverse of `dry_run`.

*`BaseCommandOptions.perthread_state`*

*Method `BaseCommandOptions.popopts(self, argv, **opt_specs)`*:
Convenience method to appply `BaseCommand.popopts` to the options (`self`).

Example for a `BaseCommand` `cmd_foo` method:

    def cmd_foo(self, argv):
        self.options.popopts(
            c_='config',
            l='long',
            x='trace',
        )
        if self.options.dry_run:
            print("dry run!")

The class attribute `COMMON_OPT_SPECS` is a mapping of
options which are always supported. `BaseCommandOptions`
has: `COMMON_OPT_SPECS={'n': 'dry_run', 'q': 'quiet', 'v': 'verbose'}`.

A subclass with more common options might extend this like so,
from `cs.hashindex`:

    COMMON_OPT_SPECS = dict(
        e='ssh_exe',
        h_='hashname',
        H_='hashindex_exe',
        **BaseCommand.Options.COMMON_OPT_SPECS,
    )

## Function `docmd(dofunc)`

Decorator for `cmd.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.GetoptError`s, issues a `warning`
  and runs `self.do_help` with the method name,
  then returns `None`
- intercepts other `Exception`s,
  issues an `exception` log message
  and returns `None`

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

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

## Function `uses_cmd_options(func, cls=<class 'cs.cmdutils.BaseCommandOptions'>, options_param_name='options')`

A decorator to provide a default parameter containing the
prevailing `BaseCommandOptions` instance as the `options` keyword
argument, using the `cs.deco.default_params` decorator factory.

This allows functions to utilitse global options set by a
command such as `options.dry_run` or `options.verbose` without
the tedious plumbing through the entire call stack.

Parameters:
* `cls`: the `BaseCommandOptions` or `BaseCommand` class,
  default `BaseCommandOptions`. If a `BaseCommand` subclass is
  provided its `cls.Options` class is used.
* `options_param_name`: the parameter name to provide, default `options`

Examples:

    @uses_cmd_options
    def f(x,*,options):
        """ Run directly from the prevailing options. """
        if options.verbose:
            print("doing f with x =", x)
        ....

    @uses_cmd_options
    def f(x,*,verbose=None,options):
        """ Get defaults from the prevailing options. """
        if verbose is None:
            verbose = options.verbose
        if verbose:
            print("doing f with x =", x)
        ....

# Release Log



*Release 20240412*:
* BaseCommand.run_context: do not store .upd and .runstate on the options (it confuses options in subcommands and we have @uses_runstate and @uses_upd forthis anyway these days).
* BaseCommand.run_context: catch SIGQUIT, present the default handler as BaseCommand.handle_signal.

*Release 20240316*:
* New @uses_cmd_options decorator to provide an "options" parameter being the prevailing BaseCommandOptions instance.
* BaseCommandOptions.popopts: get common options from BaseCommandOptions.COMMON_OPT_SPECS.

*Release 20240211*:
* Include the first sentence of the subcommand description in the short help.
* BaseCommandOptions: move the runstate_signals into this directly.
* BaseCommand: move the run() options stuff into run_context() and have it work on a copy of the original options.
* BaseCommandCmd: implement get_names(), provide docstrings for the do_* attributes, thus help.
* BaseCommand.run_context: make runstate and upd keyword only parameters.

*Release 20240201*:
* BaseCommand.run: catch CancellationError and return 1.
* BaseCommandCmd.__getattr__: recognise EOF, exit and quit to terminate the cmdloop.

*Release 20231129*:
BaseCommandOptions: define a runstate field.

*Release 20230703*:
Small internal changes.

*Release 20230612*:
* BaseCommand.cmdloop: fix intro parameter.
* Other small fixes.

*Release 20230407*:
* BaseCommand: use @uses_runstate when preparing the command, store as self.options.runstate.
* Make BaseCommandOptions a data class.
* Drop any pretence at python 2 support, we're long past that.
* BaseCommand: new cmdloop method to run a cmd.Cmd instance to run subcommand interactively.
* BaseCommand: rename shell to repl, add cmd_shell to call cmdloop().
* Drop BaseCommand.apply_defaults in favour of the Options dataclass.
* BaseCommand: do setup_logging before initiating the Options instance.

*Release 20230212*:
* BaseCommand.run_context: update RunState support.
* BaseCommand.run_context: always be having an self.options.upd.

*Release 20230211*:
BaseCommand: new shell() method to present an interactive Python prompt for use by subclasses cmd_shell method if desired.

*Release 20221228*:
Move a lot of the context logic from BaseCommand.run to BaseCommand.run_context, which now must be correctly overridden in subclasses.

*Release 20220918*:
* BaseCommand.run_context: expand default signals to include SIGHUP, expose as BaseCommand.DEFAULT_SIGNALS.
* BaseCommand.run: pass in the subclass handle_signal method if present.

*Release 20220626*:
* BaseCommand.poparg: fix positional argument handling.
* BaseCommand.poparg: new unpop_on_error=False parameter to support pushing a bad argument back onto the front of the argument list.

*Release 20220606*:
BaseCommand.run: remove the Upd bodge, too annoying, now fixed in cs.upd I believe.

*Release 20220605*:
* BaseCommand: new popopts(argv,...) compact getopt wrapper.
* BaseCommand: new poparg(argv,...) compact validating argument consumer.
* BaseCommand: drop run_argv, provided no utility.
* BaseCommand.run: get the RunState signal list from self.options.runstate_signals.
* BaseCommand.apply_opts: support multiple individual options raising GetoptError, as I hate commands which abort at the first bad option.
* Assorted other small things.

*Release 20220429*:
* BaseCommand: fold dots in argv[0] into underscores, supports subcommands like "setup.py".
* BaseCommand: new popargv(argv[,help_text[,parse[,validate[,unvalidated_message]]]]) helper class method.
* BaseCommand: accept dashed-form of the underscored_form subcommand name.
* BaseCommand: new self.options.runstate_signals=SIGINT,SIGTERM specifying singals to catch-and-cancel, shuffle run() context managers.

*Release 20220318*:
BaseCommand.__init__: handle main() method in the New Scheme.

*Release 20220315*:
_BaseSubCommand.__init__: hook in the class USAGE_KEYWORDS for methods.

*Release 20220311*:
BaseCommand: big refactor of subcommand internals and make the "cmd_foo=FooCommand" implementation work properly.

*Release 20211208*:
BaseCommand: better handle an unknown subcommand.

*Release 20210927*:
* Usage: show only the per subcommand usage for in-subcommand GetoptError.
* Usage: show terse usage when the subcommand cannot be recognised.
* Usage: support bare -h, -help, --help.

*Release 20210913*:
New BaseCommand.apply_preargv method to gather special arguments before subcommands.

*Release 20210906*:
* BaseCommand.cmd_help: bugfix obsolete parameter list.
* BaseCommand.SUBCOMMAND_ARGV_DEFAULT: support a single str value, turn into list.

*Release 20210809*:
Bugfix BaseCommand.cmd_help for modern API.

*Release 20210731*:
* BaseCommand.run: apply optional keyword arguments to self.options during the run.
* Look for self.SUBCOMMAND_ARGV_DEFAULT if no subcommand is supplied.
* Bugfix case for "main" method and no "cmd_*" methods.
* Bugfix BaseCommand.cmd_help.

*Release 20210420*:
* BaseCommand.getopt_error_handler: replace error print() with warning().
* Docstring improvements.

*Release 20210407.1*:
BaseCommand: bugfix for __init_subclass__ docstring update.

*Release 20210407*:
* BaseCommand.__init_subclass__: behave sanely if the subclass has no initial __doc__.
* BaseCommand: new .run_argv convenience method, obviates the "def main" boilerplate.

*Release 20210404*:
BaseCommand subclasses: automatically add the main usage message to the subclass docstring.

*Release 20210306*:
* BREAKING CHANGE: rework BaseCommand as a more normal class instantiated with argv and with most methods being instance methods, getting the former `options` parameter from self.options.
* BaseCommand: provide default `apply_opt` and `apply_opts` methods; subclasses will generally just override the former.

*Release 20210123*:
BaseCommand: propagate the format mapping (cmd, USAGE_KEYWORDS) to the subusage generation.

*Release 20201102*:
* BaseCommand.cmd_help: supply usage only for "all commands", full docstring for specified commands.
* BaseCommand: honour presupplied options.log_level.
* BaseCommand.usage_text: handle missing USAGE_FORMAT better.
* BaseCommand.run: provide options.upd.
* BaseCommand subclasses may now override BaseCommand.OPTIONS_CLASS (default SimpleNamespace) in order to provide convenience methods on the options.
* BaseCommand.run: separate variable for subcmd with dash translated to underscore to match method names.
* Minor fixes.

*Release 20200615*:
BaseCommand.usage_text: do not mention the "help" command if it is the only subcommand (it won't be available if there are no other subcommands).

*Release 20200521.1*:
Fix DISTINFO.install_requires.

*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.

