cs.cmdutils 20210420

a `BaseCommand` class for constructing command lines, some convenience functions for working with the `cmd` module, and some other command line related stuff

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

Latest release 20210420:

• BaseCommand.getopt_error_handler: replace error print() with warning().
• Docstring 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!
    """
    ...

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()

or via the convenience method:

MyCommand.run_argv(argv)

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

... imports etc ...
... other code ...
class MyCommand(BaseCommand):
... other code ...
if __name__ == '__main__':
    sys.exit(MyCommand.run_argv(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) method for each subcommand. 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_defaults(): prepare the initial state of self.options before any command line options are applied.
• 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 aguments 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.

Method BaseCommand.__init__(self, argv=None, *, cmd=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.
• options: a optional object for command state and context. If not specified a new SimpleNamespace is allocated for use as options, and prefilled with .cmd set to cmd and other values as set by .apply_defaults() if such a method is provided.
• cmd: optional command name for context; if this is not specified it is taken from argv.pop(0). Other keyword arguments are applied to self.options as attributes.

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_CLASS

Method BaseCommand.__init_subclass__()

Update subclasses of BaseCommand.

Appends the usage message to the class docstring.

Method BaseCommand.apply_defaults(self)

Stub apply_defaults method.

Subclasses can override this to set up the initial state of self.options.

Method BaseCommand.apply_opt(self, opt, val)

Handle a individual global command line option.

Method BaseCommand.apply_opts(self, opts)

Apply command line options.

Method BaseCommand.cmd_help(argv, options)

Usage: {cmd} [subcommand-names...] Print the help for the named subcommands, or for all subcommands if no names are specified.

Method BaseCommand.getopt_error_handler(cmd, options, e, usage)

The getopt_error_handler method is used to control the handling of GetoptErrors raised during the command line parse or during the main or cmd_subcmd` calls.

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

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.

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.

To let the exceptions out unhandled this can be overridden with a method which just returns False or even by setting the getopt_error_handler attribute to None.

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.run(self)

Run a command. Returns the exit status of the command. May raise GetoptError from subcommands.

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, called with cmd=subcmd for subcommands and with cmd=None for main.

Method BaseCommand.run_argv(argv=None)

Create an instance for argv and call its .run() method.

Method BaseCommand.run_context()

Stub context manager which surrounds main or cmd_subcmd.

Method BaseCommand.subcommand_usage_text(subcmd, fulldoc=False, usage_format_mapping=None)

Return the usage text for a subcommand.

Parameters:

• subcmd: the subcommand name
• fulldoc: if true (default False) return the full docstring with the Usage section expanded otherwise just return the Usage section.

Method BaseCommand.subcommands()

Return a mapping of subcommand names to class attributes for attributes which commence with cls.SUBCOMMAND_METHOD_PREFIX by default 'cmd_'.

Method BaseCommand.usage_text(*a, **kw)

Compute the "Usage:" message for this class from the top level USAGE_FORMAT and the 'Usage:'-containing docstrings from its cmd_* methods.

This is a cached method because it tries to update the method docstrings after formatting, which is bad if it happens more than once.

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

Release Log

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.