cs-cmdutils 20250724
Convenience functions for working with the cmd stdlib module, the BaseCommand class for constructing command line programmes, and other command line related stuff.
Keywords: python2, python3

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

*Latest release 20250724*:
* BaseCommandOptions: new empty __post_init__ so that subclasses can call super().__post_init__() unconditionally.
* New cli_datetime to parse a CLI supplied datetime specification, accepts ISO8601.

This module provides the following main items:
- `BaseCommand`: a base class for creating command line programmes
  with easier setup and usage than libraries like `optparse` or `argparse`
- `@popopts`: a decorator which works with `BaseCommand` subcommand
  methods to parse their command line options
- `@docmd`: a decorator for command methods of a `cmd.Cmd` class
  providing better quality of service

Editorial: why not arparse?
I find the whole argparse `add_argument` thing very cumbersome
and hard to use and remember.
Also, when incorrectly invoked an argparse command line prints
the help/usage messgae and aborts the whole programme with
`SystemExit`.

Short summary:
* `BaseCommand`: A base class for handling nestable command lines.
* `BaseCommandCmd`: A `cmd.Cmd` subclass used to provide interactive use of a command's subcommands.
* `BaseCommandOptions`: A base class for the `BaseCommand` `options` object.
* `cli_datetime`: Parse an ISO8601 date into a datetime. Being for the command line, this assumes the local timezone if a UTC offset is not specified.
* `docmd`: Decorator for `cmd.Cmd` subclass methods to supply some basic quality of service.
* `OptionSpec`: A class to support parsing an option value.
* `popopts`: A decorator to parse command line options from a `cmd_`*method*'s `argv` and update `self.options`.
* `qprint`: Call `print()` if `not options.quiet`. This is a compatibility shim for `qvprint()` with `verbose=not quiet` and `quiet=False`.
* `qvprint`: Call `print()` if `options.verbose` and not `options.quiet`.
* `split_usage`: Extract a `"Usage:"`paragraph from a docstring and return a 3-tuple of `(preusage,usage,postusage)`.
* `SubCommand`: An implementation for a subcommand.
* `vprint`: Call `print()` if `options.verbose`. This is a compatibility shim for `qvprint()` with `quiet=False`.

Module contents:
- <a name="BaseCommand"></a>`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):
          """ My command to do something. """

  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`.

  The `self.options` object is an instance of the class' `Options` class.
  The default comes from `BaseCommand.Options` (aka `BaseCommandOptions`)
  but classes with additional command line options will usually
  provide their own subclass:

      class MyCommand(BaseCommand):

          @dataclass
          class Options(BaseCommand.Options):
              extra_mode : str = None
              some_flag : bool = False

              # extend the common options for the new fields
              COMMON_OPT_SPECS = dict(
                  **BaseCommand.Options.COMMON_OPT_SPECS,
                  mode_=('extra_mode', 'The extra mode to do something.'),
                  flag='some_flag',
              )

  This adds an additional `--mode` *mode* and a `--flag` command line option
  which affects the fields of `self.options` and updates the
  automaticly generated usage messages accordingly.
  See the documentation for `BaseCommandOptions.popopts` for
  explaination of the `COMMON_OPT_SPECS` values.

  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
  into the main usage message automatically.

  Example:

      @popopts(l='long_mode')
      def cmd_ls(self, argv):
          """ Usage: {cmd} [-l] [paths...]
                Emit a listing for the named paths.

              Further docstring non-usage information here.
          """
          ... do the "ls" subcommand ...
          ... with use of self.options.long_mode as needed ...

  The subclass is customised by overriding the following methods:
  * `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.
  * `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 `cmd_`*subcmd* methods then method `main(argv)`
    will be called where `argv` contains the command line arguments.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):
          """ My command to do something. """

  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`.

  The `self.options` object is an instance of the class' `Options` class.
  The default comes from `BaseCommand.Options` (aka `BaseCommandOptions`)
  but classes with additional command line options will usually
  provide their own subclass:

      class MyCommand(BaseCommand):

          @dataclass
          class Options(BaseCommand.Options):
              extra_mode : str = None
              some_flag : bool = False

              # extend the common options for the new fields
              COMMON_OPT_SPECS = dict(
                  **BaseCommand.Options.COMMON_OPT_SPECS,
                  mode_=('extra_mode', 'The extra mode to do something.'),
                  flag='some_flag',
              )

  This adds an additional `--mode` *mode* and a `--flag` command line option
  which affects the fields of `self.options` and updates the
  automaticly generated usage messages accordingly.
  See the documentation for `BaseCommandOptions.popopts` for
  explaination of the `COMMON_OPT_SPECS` values.

  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 `Example:

      @popopts(l='long_mode')
      def cmd_ls(self, argv):
          """ Usage: {cmd} [-l] [paths...]
                Emit a listing for the named paths.

              Further docstring non-usage information here.
          """
          ... do the "ls" subcommand ...
          ... with use of self.options.long_mode as needed ...

  The subclass is customised by overriding the following methods:
  * `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.
  * `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 `cmd_`*subcmd* methods then method `main(argv)`
    will be called where `argv` contains the command line arguments.

  Usage summary:

      Usage: ` then that paragraph is incorporated
        into the main usage message automatically.

*`BaseCommand.__init__(self, argv=None, *, cmd=None, options=None, **kw_options) -> str`*:
Initialise the command line.
Return the subcommand name, or `None` if there is only `main`.
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`*

*`BaseCommand.SubCommandClass`*

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

This default implementation raises a `NotImplementedError`.
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.

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

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

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

This default implementation does nothing.

*`BaseCommand.cmd_help(self, argv)`*:
Usage: {cmd} [-l] [-s] [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.
Options:
  -l  Long listing.
  -r  Recurse into subcommands.
  -s  Short listing.

*`BaseCommand.cmd_info(self, argv, *, field_names=None, skip_names=None)`*:
Usage: {cmd} [field-names...]
  Recite general information.
  Explicit field names may be provided to override the default listing.

This default method recites the values from `self.options`,
excluding those enumerated by `self.options.INFO_SKIP_NAMES`.

This base method provides two optional parameters to allow
subclasses to tune its behaviour:
- `field_namees`: an explicit list of options attributes to print
- `skip_names`: a list of option attributes to not print,
  default from `self.options.INFO_SKIP_NAMES`

*`BaseCommand.cmd_repl(self, argv)`*:
Usage: {cmd}
Run a REPL (Read Evaluate Print Loop), an interactive Python prompt.
Options:
  --banner banner  Banner.

*`BaseCommand.cmd_shell(*a, upd: Optional[cs.upd.Upd] = <function uses_upd.<locals>.<lambda> at 0x1065c94e0>, **kw)`*:
Usage: {cmd}
Run a command prompt via cmd.Cmd using this command's subcommands.

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

*`BaseCommand.extract_usage(cmd=None)`*:
Extract the `Usage:` paragraph from `cls__doc__` if present.
Return a 2-tuple of `(doc_without_usage,usage_text)`
being the remaining docstring and a full usage message.

*Note*: this actually sets `cls.USAGE_FORMAT` if that does
not already exist.

*`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.

*`BaseCommand.handle_signal(self, sig, frame, *, runstate: Optional[cs.resources.RunState] = <function uses_runstate.<locals>.<lambda> at 0x1065c89a0>)`*:
The default signal handler, which cancels the default `RunState`.

*`BaseCommand.has_subcommands()`*:
Test whether the class defines additional subcommands.

*`BaseCommand.method_cmdname(method_name: str)`*:
The `cmd` value from a method name.

*`BaseCommand.poparg(argv: List[str], *specs, unpop_on_error: bool = False, opt_spec_class=None)`*:
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 size: size > 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']

*`BaseCommand.popopts(self, argv, options, **opt_specs)`*:
OBSOLETE version of popopts, suggestion: self.options.popopts

A convenience shim which returns `self.options.popopts(argv,**opt_specs)`.

*`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`

*`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.

*`BaseCommand.run_context(*a, upd: Optional[cs.upd.Upd] = <function uses_upd.<locals>.<lambda> at 0x1065c8900>, **kw)`*:
The context manager which surrounds `main` or `cmd_`*subcmd*.
Normally this will have a bare `yield`, but you can yield
a not `None` value to exit before the command, for example
if the run setup fails.

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 ...

This base implementation does the following things:
- provides a `self.options` which is a copy of the original
  `self.options` so that it may freely be modified during the
  command
- provides a prevailing `RunState` as `self.options.runstate`
  if one is not already present
- provides a `cs.upd.Upd` context for status lines
- catches `self.options.runstate_signals` and handles them
  with `self.handle_signal`

*`BaseCommand.subcommand`*

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

*`BaseCommand.subcommands`*

*`BaseCommand.usage_text(self, **subcommand_kw)`*:
Compute the "Usage:" message for this class.
Parameters are as for `SubCommand.usage_text`.
- <a name="BaseCommandCmd"></a>`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 and calls its `.cmdloop()` method
  i.e. `cmd.Cmd.cmdloop`.

*`BaseCommandCmd.get_names(self)`*:
Return a list of the subcommand names.
- <a name="BaseCommandOptions"></a>`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`
  * `.ssh_exe='ssh'`
  * `.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 ...

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

Example showing the semantics:

    >>> from cs.cmdutils import BaseCommandOptions
    >>> @dataclass
    ... class DemoOptions(BaseCommandOptions):
    ...   x: int = 0
    ...
    >>> options = DemoOptions(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

*`BaseCommandOptions.__post_init__(self)`*:
A empty base post `__init__` method so that all subclasses'
`__post_init__`s  can call their `super().__post_init__`.

*`BaseCommandOptions.as_dict(self)`*:
Return the options as a `dict`.
This contains all the public attributes of `self`.

*`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.

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

*`BaseCommandOptions.fields_as_dict(self)`*:
Return the options' fields as a `dict`.
This contains all the field values of `self`.

*`BaseCommandOptions.getopt_spec_map(opt_specs_kw: Mapping, common_opt_specs=None)`*:
Return a 3-tuple of (shortopts,longopts,getopt_spec_map)` being:
- `shortopts`: the `getopt()` short options specification string
- `longopts`: the `getopts()` long option specification list
- `getopt_spec_map`: a mapping of `opt`->`OptionSpec`
  where `opt` is as from `opt,val` from `getopt()`
  and `opt_spec` is the associated `OptionSpec` instance

*`BaseCommandOptions.opt_spec_class`*

*`BaseCommandOptions.perthread_state`*

*`BaseCommandOptions.popopts(self, argv, **opt_specs_kw)`*:
Parse option switches from `argv`, a list of command line strings
with leading option switches and apply them to `self`.
Modify `argv` in place.

Example use in a `BaseCommand` `cmd_foo` method:

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

The expected options are specified by the keyword parameters
in `opt_specs`.
Each keyword name has the following semantics:
* 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'`.

The `BaseCommand` class provides a `popopts` method
which is a shim for this method applied to its `.options`.
So common use in a command method usually looks like this:

    class SomeCommand(BaseCommand):

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

The `self.options` object is preprovided as an instance of
the `self.Options` class, which is `BaseCommandOptions` by
default. There is presupplies support for some basic options
like `-v` for "verbose" and so forth, and a subcommand
need not describe these in a call to `self.options.popopts()`.

Example:

    >>> import os.path
    >>> from typing import Optional
    >>> @dataclass
    ... class DemoOptions(BaseCommandOptions):
    ...   all: bool = False
    ...   jobs: int = 1
    ...   number: int = 0
    ...   once: bool = False
    ...   path: Optional[str] = None
    ...   trace_exec: bool = False
    ...
    >>> options = DemoOptions()
    >>> argv = ['-1', '-v', '-y', '-j4', '--path=/foo', 'bah', '-x']
    >>> opt_dict = options.popopts(
    ...   argv,
    ...   _1='once',
    ...   a='all',
    ...   j_=('jobs',int),
    ...   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 # doctest: +ELLIPSIS
    DemoOptions(cmd=None, dry_run=False, force=False, quiet=False, runstate_signals=(...), verbose=True, all=False, jobs=4, number=0, once=True, path='/foo', trace_exec=False)

*`BaseCommandOptions.update(self, **updates)`*:
Modify the options in place with the mapping `updates`.
It would be more normal to call the options in a `with` statement
as shown for `__call__`.

*`BaseCommandOptions.usage_options_format(headline='Options:', *, _common_opt_specs=None, **opt_specs_kw)`*:
Return an options paragraph describing `opt_specs_kw`.
or `''` if `opt_specs_kw` is empty.
- <a name="cli_datetime"></a>`cli_datetime(dt_s: str) -> datetime.datetime`: Parse an ISO8601 date into a datetime.
  Being for the command line, this assumes the local timezone
  if a UTC offset is not specified.
- <a name="docmd"></a>`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 ...
- <a name="OptionSpec"></a>`class OptionSpec`: A class to support parsing an option value.

*`OptionSpec.__post_init__(self)`*:
Infer `field_name` and `help_text` if unspecified.

*`OptionSpec.add_argument(self, parser, options=None)`*:
Add this option to an `argparser`-style option parser.
The optional `options` parameter may be used to supply an
`Options` instance to provide a default value.

*`OptionSpec.from_opt_kw(opt_k: str, specs: Union[str, List, Tuple, NoneType])`*:
Factory to produce an `OptionSpec` from a `(key,specs)` 2-tuple
as from the `items()` from a `popopts()` call.

The `specs` is normally a list or tuple, but a bare string
will be promoted to a 1-element list containing the string.

The elements of `specs` are considered in order for:
- an identifier specifying the `arg_name`,
  optionally prepended with a dash to indicate an inverted option
- a help text about the option
- a callable to parse the option string value to obtain the actual value
- a callable to validate the option value
- a message for use when validation fails

*`OptionSpec.getopt_long`*:
The option specification for a getopt long option.
Return `None` if `self.opt_name` is only 1 character.

*`OptionSpec.getopt_opt`*:
The `opt` we expect from `opt,val=getopt(argv,...)`.

*`OptionSpec.getopt_short`*:
The option specification for a getopt short option.
Return `''` if `self.opt_name` is longer than 1 character.

*`OptionSpec.help_text_from_field_name(field_name)`*:
Compute an inferred `help_text` from an option `field_name`.

*`OptionSpec.needs_arg`*:
Whether we expect an argument: we have a `self.arg_name`.

*`OptionSpec.option_terse(self)`*:
Return the `"-x"` or `"--name"` option string (with the arg name if expected).

*`OptionSpec.option_usage(self)`*:
A 2 line usage entry for this option.

Example:

    -j jobs
      Job limit.

*`OptionSpec.parse_value(self, value)`*:
Parse `value` according to the spec.
Raises `GetoptError` for invalid values.
- <a name="popopts"></a>`popopts(*da, **dkw)`: A decorator to parse command line options from a `cmd_`*method*'s `argv`
  and update `self.options`. This also updates the method's usage message.

  Example:

      @popopts(x=('trace', 'Trace execution.'))
      def cmd_do_something(self, argv):
          """ Usage: {cmd} [-x] blah blah
                Do some thing to blah.
          """

  This arranges for cmd_do_something to call `self.options.popopts(argv)`,
  and updates the usage message with an "Options:" paragraph.

  This avoids needing to manually enumerate the options in the
  docstring usage and avoids explicitly calling `self.options.popopts`
  inside the method.
- <a name="qprint"></a>`qprint(*print_a, quiet: bool, **qvprint_kw)`: Call `print()` if `not options.quiet`.
  This is a compatibility shim for `qvprint()` with `verbose=not
  quiet` and `quiet=False`.
- <a name="qvprint"></a>`qvprint(*print_a, quiet, verbose, **print_kw)`: Call `print()` if `options.verbose` and not `options.quiet`.
- <a name="split_usage"></a>`split_usage(doc: Optional[str], usage_marker='Usage:') -> Tuple[str, str, str]`: Extract a `"Usage:"`paragraph from a docstring
  and return a 3-tuple of `(preusage,usage,postusage)`.

  If the usage paragraph is not present `''` is returned as
  the middle comonpent, otherwise it is the unindented usage
  without the leading `"Usage:"`.
- <a name="SubCommand"></a>`class SubCommand`: An implementation for a subcommand.

*`SubCommand.__call__(self, argv: List[str])`*:
Run the subcommand.

Parameters:
* `argv`: the command line arguments after the subcommand name

*`SubCommand.get_cmd(self) -> str`*:
Return the `cmd` string for this `SubCommand`,
derived from the subcommand's method name or class name
if `self.cmd` is not set.

*`SubCommand.get_subcmds(self)`*:
Return the names of `self.method`'s subcommands in lexical order.

*`SubCommand.get_subcommands(self)`*:
Return `self.method`'s mapping of subcommand name to `SubCommand`.

*`SubCommand.get_usage_format(self, show_common=False) -> str`*:
Return the usage format string for this subcommand.
*Note*: no leading "Usage:" prefix.
If `show_common` is true, include the `Common options:` paragraph.

*`SubCommand.get_usage_keywords(self, *, cmd: Optional[str] = None, usage_mapping: Optional[Mapping] = None) -> str`*:
Return a mapping to be used when formatting the usage format string.

This is an elaborate `ChainMap` of:
- the optional `cmd` or `self.get_cmd()`
- the optional `usage_mapping` parameter
- `self.usage_mapping`
- `self.method.USAGE_KEYWORDS` if present
- the attributes of `self.command`
- the attributes of `type(self.command)`
- the attributes of the module for `type(self.command)`

*`SubCommand.has_subcommands(self)`*:
Whether this `SubCommand`'s `.method` has subcommands.

*`SubCommand.instance`*:
An instance of the class for `self.method`.

*`SubCommand.short_subusages(self, subcmds: List[str], *, recurse=False, short=False)`*:
Return a list of tabulated one line subcommand summaries.

*`SubCommand.subusage_table(self, subcmds: List[str], *, recurse=False, short=False)`*:
Return rows for use with `cs.lex.tabulate`
for the short subusage listing.

*`SubCommand.usage_text(self, *, cmd=None, short: bool, recurse: bool = False, show_common: bool = False, show_subcmds: Union[bool, str, List[str], NoneType] = None, usage_mapping: Optional[Mapping] = None, seen_subcommands: Optional[Mapping] = None) -> str`*:
Return the filled out usage text for this subcommand.
- <a name="vprint"></a>`vprint(*print_a, **qvprint_kw)`: Call `print()` if `options.verbose`.
  This is a compatibility shim for `qvprint()` with `quiet=False`.

# Release Log



*Release 20250724*:
* BaseCommandOptions: new empty __post_init__ so that subclasses can call super().__post_init__() unconditionally.
* New cli_datetime to parse a CLI supplied datetime specification, accepts ISO8601.

*Release 20250531.1*:
Fix precedence of subcommand options over inherited common options.

*Release 20250531*:
* Fix @popopts internals for recent @decorator internal changes.
* Fix BaseCommandOptions.getopt_spec_map to let the subcommand options override the inherited common options.
* Fix a format string.

*Release 20250528*:
New qprint() which prints if not quiet a bit like vprint(), which prints if verbose and not quiet.

*Release 20250426*:
Minor changes.

*Release 20250418*:
* BaseCommand: honour SUBCOMMAND_ARGV_DEFAULT even when there are no subcommands.
* BaseCommand._prerun_setup: bugfix application of default argv, was setting self._argv too early.
* Some documentation updates.

*Release 20250306*:
If a subcommand raises GetoptError, only show the usage for that subcommand.

*Release 20250103*:
BaseCommand.cmd_info: default skip_names is self.options.INFO_SKIP_NAMES.

*Release 20241222.1*:
* BaseCommand.cmd_info: use pformat instead of str.
* BaseCommand.cmd_repl: enumerate the options as top level names in the banner.
* If run as main programme, run a demo command.

*Release 20241222*:
BaseCommand.cmd_info: use compact=True with the pforat() call.

*Release 20241218*:
BaseCommand: add cmd_repl to the default subcomands.

*Release 20241212*:
SubCommand.short_subusages: use a single tabluate() table for the entire recursive listing, produces a much more readable short listing.

*Release 20241207*:
BaseCommandOptions.usage_options_format: support multiline help text via the new tabulate support.

*Release 20241206.1*:
SubComand.usage_text: normalise the show_subcmds to match the subcommands mapping.

*Release 20241206*:
* New @popopts decorator to run self.options.popopts and fill out the usage message.
* Add "-e ssh-command" and the .ssh_exe attribute to BaseCommandOptions.

*Release 20241122.2*:
* OptionSpec.getopt_long: fix construction of getopt long option specifications, lost during the recent refactor.
* Two other minor fixes.

*Release 20241122.1*:
* SubCommand.usage_format_parts: backport type annotation for older Pythons.
* BaseCommand.extract_usage: update parameters for usage_text().

*Release 20241122*:
* BaseCommand.cmd_help: new -l (long), -r (recurse) and -s (short, not long) options.
* A big rework of the help/usage output; still one rough edge left.
* BaseCommandOptions.popopts: infill with False instead of None for missing boolean options.
* SubCommand: a few new methods and properties to expose various operations.
* BaseCommand._prerun_setup: revert SUBCOMMAND_ARGV_DEFAULT to None, make a missing subcommand run "help -s" when there's no SUBCOMMAND_ARGV_DEFAULT.

*Release 20241119*:
* SubCommand.usage_text: small improvements and a fix.
* New BaseCommand.SubCommandClass attribute for the SubCommand subclass, supports using additional SubCommand subclasses for eg cs.djutils.

*Release 20241117*:
* _COMMON_OPT_SPECS: include a --dry-run option, alter for -n.
* SubCommand.usage_text: one line listing for common subcommands.

*Release 20241110*:
* Various fixes and enhancements to the usage text generation.
* BaseCommandOptions.COMMON_OPT_SPECS stuff, including inheritance and presentation in usage.
* BaseCommand.run: if self.run_context() yields not None, exit immediately with that value.
* Rationalise and improve OptionSpec.
* Supplant vprint with qvprint which honours quiet and verbose, provide vprint as a shim with a hardwired quiet=False.
* Make cmd_info the default subcommand and make some improvements.
* BaseCommandOptions: new fields_as_dict method, update copy() to start with fields_as_dict, overlay as_dict, overlay updates.
* OptionSpec: new add_argument(parser[,options]) method to add this option to an argparse style option parser (again, for the upcoming cs.djutils module).
* A heap of small things.

*Release 20241007*:
* BaseCommand: drop __init_subclass__, was doing too much to early.
* BaseCommand.__init__: no cmd and argv[0] ends with ".py" infer cmd from the class name.
* Other minor updates.

*Release 20241005*:
* BaseCommand: provide an options.runstate to allow the command to override the default (almost never happens).
* BaseCommand.popopts: fix reference to OptionSpec class.
* BaseCommand.run: put the try/except:CancellationError outside the self.run_context context manager call, as it can directly raise CancellationError.
* New vprint() function calling print() if options.verbose.

*Release 20240709*:
BaseCommand: support putting the top level Usage in the class docstring instead of as .USAGE_FORMAT, append full usage to the class docstring in `BaseCommand.__init_subclass__`.

*Release 20240630*:
* BaseCommand: make SUBCOMMAND_ARGV_DEFAULT be 'shell' for an interactive prompt, still a little unsure how sensible this is, aiming at the very cool submode stuff from the Cisco switch config command line.
* BaseCommandOptions: new as_dict() method.
* New SubCommand.usage_text() to compose the full usage text for this SubCommand.
* Many small improvements and internal refactors.

*Release 20240519*:
BaseCommand.run_context: attach the runstate to the options.

*Release 20240422*:
* BaseCommandOptions.popopts: return the dict from BaseCommand.popopts().
* BaseCommand.apply_preargv: apply the default options supported by self.options.
* BaseCommandOptions.update(mapping) method, useful for dropping subcommand-specific defaults onto the options ahead of the local popopts() call.

*Release 20240412*:
* BaseCommand.run_context: do not store .upd and .runstate on the options (it confuse