cli: Application command line support

This module provides a method for parsing text commands and calling the functions that implement them. First, commands are registered with a description of the arguments they take, and with a function that implements the command. Later, a Command instance is used to parse a command line, and optionally execute the command. Incomplete command lines are supported, so possible commands can be suggested.

In addition to registering command functions, there is a separate mechanism to support textual Command Aliases.

Text Commands

Synopsis:

command_name rv1 rv2 [ov1 [ov2]] [kn1 kv1] [kn2 kv2]

Text commands are composed of a command name, which can be multiple words, followed by required positional arguments, rvX, optional positional arguments, ovX, and keyword arguments with a value, knX kvX. Each argument has an associated Python argument name (for keyword arguments it is the keyword, knX). rvX, ovX, and kvX are the type-checked values. If the argument name is the same as a Python keyword, then an underscore appended to it to form the Python argument name. The names of the optional arguments are used to let them be given as keyword arguments as well. Multiple value arguments are separated by commas and the commas may be followed by whitespace. Depending on the type of an argument, e.g., a color name, whitespace can also appear within an argument value. Argument values may be quoted with double quotes. And in quoted text, Python’s textual escape sequences are recognized, e.g., \N{LATIN CAPITAL LETTER A WITH RING ABOVE} for the ångström sign, Å.

Words in the command name may be truncated and are automatically completed to the first registered command with the given prefix. Likewise for keyword arguments.

Keywords are case sensitive, and are expected to be all lowercase. Underscores are supported, but are documented as and accepted as dashes. For example, a bg_color keyword would be documented as bg-color.

Registering Commands

To add a command, register() the command name, a description of the arguments it takes, and the function to call that implements the command. Command registration can be partially delayed to avoid importing the command description and function until needed. See register() and delay_registration() for details.

The description is either an instance of the Command Description class, CmdDesc, or a tuple with the arguments to the initializer. The CmdDesc initializer takes tuples describing the required, optional, and keyword arguments. Each tuple contains tuples with the argument name and a type annotation (see below). Postconditions (see below) can be given too.

Command Functions

The command function arguments are expected to start with a session argument. The rest of the arguments are assembled as keyword arguments, as built from the command line and the command description. The initial session argument to a command function is not part of the command description.

Type Annotations

There are many standard type notations and they should be reused as much as possible:

Type Annotation
bool BoolArg
float FloatArg
int IntArg
str StringArg
tuple of 3 bool Bool3Arg
tuple of 3 float Float3Arg
tuple of 3 int Int3Arg
list of float FloatsArg
list of int IntsArg

There is one special annotation: RestOfLine that consumes the rest of the command line as text.

Annotations are used to parse text and convert it to the appropriate type. Annotations can be extended with various specializers:

Specializer Example
Bounded Bounded(FloatArg, 0.0, 100.0)
ListOf ListOf(FloatArg) a.k.a., FloatsArg
SetOf SetOf(IntArg)
TupleOf TupleOf(FloatArg, 3) a.k.a., Float3Arg
Or Or(FloatArg, StringArg) discouraged
EnumOf enumerated values

Creating Your Own Type Annotation

Annotations perform several functions: (1) to convert text to a value of the appropriate type, and (2) to give reasonable error messages.

See the Annotation documentation for details.

Example

Here is a simple example:

import from chimera.core.commands import cli, errors
@register("echo", cli.CmdDesc(optional=[('text', cli.RestOfLine)]))
def echo(session, text=''):
    print(text)
...
command = cli.Command(session)
command.parse_text(text, final=True)
try:
    status = command.execute()
    if status:
        print(status)
except errors.UserError as err:
    print(err, file=sys.stderr)

Command Aliases

Normally, command aliases are made with the alias command, but they can also be explicitly register with alias() and removed with unalias().

An alias definition uses $n to refer to passed in arguments. $1 may appear more than once. $$ is $.

To register a multiword alias, quote the command name.

class Aggregate(annotation, min_size=None, max_size=None, name=None, prefix=None)

Bases: chimera.core.commands.cli.Annotation

Common class for collections of values.

Aggregate(annotation, constructor, add_to, min_size=None, max_size=None,
name=None) -> annotation
Parameters:
  • annotation – annotation for values in the collection.
  • min_size – minimum size of collection, default None.
  • max_size – maximum size of collection, default None.
  • name – optionally override name in error messages.

This class is typically used via ListOf, SetOf, or TupleOf. The comma separator for aggregate values is handled by the Command class, so parsing is delegated to the underlying annotation.

Subclasses need to set the constructor attribute and replace the add_to method.

add_to(container, element)

Add to add an element to the container

Parameters:
  • container – the container to add elements to
  • element – the element to add to the container
Returns:

None for mutable containers, or a new container if immutable.

class Alias(text)

Bases: object

alias a command

Returns a callable unnamed command alias.

Parameters:text – parameterized command text

The text is scanned for $n, where n is the n-th argument, $* for the rest of the line, and $$ for a single $.

cmd_desc(**kw)

Return CmdDesc instance for alias

The CmdDesc keyword arguments other than ‘required’, ‘optional’, and ‘keyword’ can be used.

class Annotation

Bases: object

Base class for all annotations

Each annotation should have the following attributes:

name

Set to textual description of the annotation, including the leading article, e.g., “a truth value”.

static parse(text, session)

Convert text to appropriate type.

Parameters:
  • text – command line text to parse
  • session – for session-dependent data types
Returns:

3-tuple with the converted value, consumed text (possibly altered with expanded abbreviations), and the remaining unconsumed text

Raises ValueError:
 

if unable to convert text

The leading space in text must already be removed. It is up to the particular annotation to support abbreviations.

url = None

URL for help information

exception AnnotationError(message, offset=None)

Bases: chimera.core.errors.UserError, ValueError

Error, with optional offset, in annotation

class AtomicStructuresArg

Bases: chimera.core.commands.cli.Annotation

Parse command atomic structures specifier

class AtomsArg

Bases: chimera.core.commands.cli.Annotation

Parse command atoms specifier

class AxisArg

Bases: chimera.core.commands.cli.Annotation

Annotation for axis vector that can be 3 floats or “x”, or “y”, or “z”

class BoolArg

Bases: chimera.core.commands.cli.Annotation

Annotation for boolean literals

class Bounded(annotation, min=None, max=None, name=None)

Bases: chimera.core.commands.cli.Annotation

Support bounded numerical values

Bounded(annotation, min=None, max=None, name=None) -> an Annotation

Parameters:
  • annotation – numerical annotation
  • min – optional lower bound
  • max – optional upper bound
  • name – optional explicit name for annotation
class CmdDesc(required=(), optional=(), keyword=(), postconditions=(), url=None, synopsis=None, official=False)

Bases: object

Describe command arguments.

Parameters:
  • required – required positional arguments tuple
  • optional – optional positional arguments tuple
  • keyword – keyword arguments tuple
  • url – URL to help page
  • synopsis – one line description
  • official – True if officially supported command

Each tuple contains tuples with the argument name and a type annotation. The command line parser uses the optional argument names to as keyword arguments.

copy()

Return a copy suitable for use with another function.

class Command(session, text='', final=False, _used_aliases=None)

Bases: object

Keep track of (partially) typed command with possible completions

Parameters:
  • text – the command text
  • final – true if text is the complete command line (final version).
error_check()

Error check results of calling parse_text

Raises UserError:
 if parsing error is found

Separate error checking logic from execute() so it may be done separately

execute(_used_aliases=None)

If command is valid, execute it with given session.

parse_text(text, final=False, no_aliases=False, _used_aliases=None)

Parse text into function and arguments

Parameters:
  • text – The text to be parsed.
  • final – True if last version of command text.
  • no_aliases – True if aliases should not be considered.

May be called multiple times. There are a couple side effects:

  • The automatically completed text is put in self.current_text.
  • Possible completions are in self.completions.
  • The prefix of the completions is in self.completion_prefix.
class DottedTupleOf(annotation, min_size=None, max_size=None, name=None, prefix=None)

Bases: chimera.core.commands.cli.Aggregate

Annotation for dot-separated lists of a single type

DottedListOf(annotation, min_size=None, max_size=None) -> annotation

constructor

alias of tuple

class EnumOf(values, ids=None, name=None)

Bases: chimera.core.commands.cli.Annotation

Support enumerated types

EnumOf(values, ids=None, name=None) -> an Annotation

Parameters:
  • values – sequence of values
  • ids – optional sequence of identifiers
  • name – optional explicit name for annotation

If the ids are given, then there must be one for each and every value, otherwise the values are used as the identifiers. The identifiers must all be strings.

class FloatArg

Bases: chimera.core.commands.cli.Annotation

Annotation for floating point literals

class IntArg

Bases: chimera.core.commands.cli.Annotation

Annotation for integer literals

class Limited(name, min=None, max=None)

Bases: chimera.core.commands.cli.Postcondition

Bounded numerical values postcondition

Limited(name, min=None, max=None) -> Postcondition

Parameters:
  • name – name of argument to check
  • min – optional inclusive lower bound
  • max – optional inclusive upper bound

If possible, use the Bounded annotation because the location of the error is the beginning of the argument, not the end of the line.

class ListOf(annotation, min_size=None, max_size=None, name=None, prefix=None)

Bases: chimera.core.commands.cli.Aggregate

Annotation for lists of a single type

ListOf(annotation, min_size=None, max_size=None) -> annotation

constructor

alias of list

class NoArg

Bases: chimera.core.commands.cli.Annotation

Annotation for keyword with no value

class Or(*annotations, name=None)

Bases: chimera.core.commands.cli.Annotation

Support two or more alternative annotations

Or(annotation, annotation [, annotation]*, name=None) -> an Annotation

Parameters:name – optional explicit name for annotation
class Postcondition

Bases: object

Base class for postconditions

check(kw_args)

Assert arguments match postcondition

Parameters:kw_args – dictionary of arguments that will be passed to command callback function.
Returns:True if arguments are consistent
error_message()

Appropriate error message if check fails.

Returns:error message
class RequiredArgs(*arg_names)

Bases: chimera.core.commands.cli.Postcondition

Postcondition check for required keywords

RequiredArgs(argument name(s)) -> a RequiredArgs object

Parameters:*arg_names

list of argument names

This is useful for ‘optional’ and keyword arguments that don’t have a default value.

class SameSize(name1, name2)

Bases: chimera.core.commands.cli.Postcondition

Postcondition check for same size arguments

SameSize(name1, name2) -> a SameSize object

Parameters:
  • name1 – name of first argument to check
  • name2 – name of second argument to check
class SetOf(annotation, min_size=None, max_size=None, name=None, prefix=None)

Bases: chimera.core.commands.cli.Aggregate

Annotation for sets of a single type

SetOf(annotation, min_size=None, max_size=None) -> annotation

constructor

alias of set

class StringArg

Bases: chimera.core.commands.cli.Annotation

Annotation for text (a word or quoted)

class TupleOf(annotation, size, name=None)

Bases: chimera.core.commands.cli.Aggregate

Annotation for tuples of a single type

TupleOf(annotation, size) -> annotation

constructor

alias of tuple

add_keyword_arguments(name, kw_info)

Make known additional keyword argument(s) for a command

Parameters:
  • name – the name of the command (must not be an alias)
  • kw_info – { keyword: annotation }
alias(session, name='', text='')

Create command alias

Parameters:
  • name – optional name of the alias
  • text – optional text of the alias

If the alias name is not given, then a text list of all the aliases is returned. If alias text is not given, the the text of the named alias is returned. If both arguments are given, then a new alias is made.

command_function(name, no_aliases=False)

Return callable for given command name

Parameters:
  • name – the name of the command
  • no_aliases – True if aliases should not be considered.
Returns:

the callable that implements the command

command_url(name, no_aliases=False)

Return help URL for given command name

Parameters:
  • name – the name of the command
  • no_aliases – True if aliases should not be considered.
Returns:

the URL registered with the command

delay_registration(name, proxy_function, logger=None)

delay registering a named command until needed

Parameters:
  • proxy_function – the function to call if command is used
  • logger – optional logger

The proxy function should explicitly reregister the command or register subcommands and return nothing.

Example:

from chimera.core.commands import cli

def lazy_reg():
    import module
    cli.register('cmd subcmd1', module.subcmd1_desc, module.subcmd1)
    cli.register('cmd subcmd2', module.subcmd2_desc, module.subcmd2)

cli.delay_registration('cmd', lazy_reg)
deregister(name)

Remove existing command

If the command was an alias, the previous version is restored

html_usage(name, no_aliases=False)

Return usage string in HTML for given command name

Parameters:
  • name – the name of the command
  • no_aliases – True if aliases should not be considered.
Returns:

a HTML usage string for the command

is_python_keyword()

x.__contains__(y) <==> y in x.

next_token(text)

Extract next token from given text.

Parameters:text – text to parse without leading whitespace
Returns:a 3-tuple of first argument in text, the actual text used, and the rest of the text.

Tokens may be quoted, in which case the text between the quotes is returned.

register(name, cmd_desc=(), function=None, logger=None)

register function that implements command

Parameters:
  • name – the name of the command and may include spaces.
  • cmd_desc – information about the command, either an instance of CmdDesc, or the tuple with CmdDesc parameters.
  • function – the callback function.
  • logger – optional logger

If the function is None, then it assumed that register() is being used as a decorator.

To delay introspecting the function until it is actually used, register using the delay_registration() function.

For autocompletion, the first command registered with a given prefix wins. Registering a command that is a prefix of an existing command is an error since it breaks backwards compatibility.

registered_commands()

Return a list of the currently registered commands

unalias(session, name)

Remove command alias

Parameters:name – name of the alias
unescape(text)

Replace backslash escape sequences with actual character.

Parameters:text – the input text
Returns:the processed text

Follows Python’s string literal syntax for escape sequences.

unescape_with_index_map(text)

Replace backslash escape sequences with actual character.

Parameters:text – the input text
Returns:the processed text and index map from processed to input text

Follows Python’s string literal syntax for escape sequences.

usage(name, no_aliases=False)

Return usage string for given command name

Parameters:
  • name – the name of the command
  • no_aliases – True if aliases should not be considered.
Returns:

a usage string for the command