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Simple command line argument parser for Python

Project description

QuickParse

Simple command line argument parser for Python

Example

list_things.py:

from quickparse import QuickParse

def list_things(a_list, quickparse):
    if quickparse.numeric:
        if isinstance(quickparse.numeric, tuple):
            print(', '.join(map(str, a_list[:quickparse.numeric[-1]])))
        else:
            print(', '.join(map(str, a_list[:quickparse.numeric])))
    else:
        print("How many items? Give a numeric value like '-3'")

commands_config = {
    'ls': list_things,
    '': lambda: print("Command is missing, use 'ls'"),
}

things = ['apple', 'banana', 'blueberry', 'orange', 'pear', 'pineapple']

QuickParse(commands_config).execute(things)

Run it:

$ python list_things.py ls -5
apple, banana, blueberry, orange, pear

The way it works:

  • commands_config tells QuickParse to look for ls as a command and call list_things on it - when no commands show help
  • QuickParse parses arguments as normal while ls is privileged as a command
  • QuickParse finds -5 so it adds as quickparse.numeric = 5 (quickparse being the QuickParse instance that otherwise would come as quickparse = QuickParse(commands_config))
  • QuickParse sees list_things being associated to ls, so quickparse.execute(things) calls it, passing on the arguments of execute(..) - one positional argument in this case
  • since list_things expects a named argument quickparse, QuickParse makes sure it passes on the reference to its own instance of quickparse
  • if there are multiple numeric flags are given all are passed down with quickparse.numeric in a tuple

GNU Argument Syntax implementation with extensions

GNU Argument Syntax: https://www.gnu.org/software/libc/manual/html_node/Argument-Syntax.html

Extensions

Numeric '-' values

$ my_cmd -12

Numeric '+' values

$ my_cmd +12

Long '-' options - only with explicit config

$ my_cmd -list

By default it becomes -l -i -s -t, but adding QuickParse(options_config = [ ('-list', ) ]) will stop unpacking.

Long '+' options by default

$ my_cmd +list

Equivalent options - using options_config

$ my_cmd -l

is equivalent to

$ my_cmd --list

if adding QuickParse(options_config = [ ('-l', '--list') ])

Command-subcommand hierarchy and function bindings - using commands_config

Defining a random sample from git looks like this:

commands_config = {
    '': do_show_help,
    'commit': do_commit,
    'log': do_log,
    'stash': {
        '': do_stash,
        'list': do_stash_list,
    }
}

options_config = [
    ('-a', '--all'),
]

QuickParse(commands_config, options_config).execute()

Commands are called according to commands_config.
That is $ git log -3 calls do_log
do_log may look like this:

def do_log(quickparse):
    print(get_log_entries()[:quickparse.numeric])

If there is a named argument in do_log's signature called quickparse, the instance coming from QuickParse(commands_config, options_config) is passed down holding all the results of parsing.
Parsing happens by using the defaults and applying what options_config adds to it.

Argument Formats

               Argument Format                               Example                Remarks
-<number> $ my_cmd -12 (default)
+<number> $ my_cmd +12 (default)
-<single_letter> $ my_cmd -x (default)
+<single_letter> $ my_cmd +x (default)
-<single_letter><value> $ my_cmd -nFoo unpacking is the default: -n -F -o
options_config needs a type entry saying it expects a value (other than bool)
+<single_letter><value> $ my_cmd +nFoo unpacking is the default: +n +F +o
options_config needs a type entry saying it expects a value (other than bool)
-<single_letter>=<value> $ my_cmd -n=Foo (default)
+<single_letter>=<value> $ my_cmd +n=Foo (default)
-<single_letter> <value> $ my_cmd -n Foo options_config needs a type entry saying it expects a value (other than bool)
+<single_letter> <value> $ my_cmd +n Foo options_config needs a type entry saying it expects a value (other than bool)
-<letters> $ my_cmd -abc unpacking is the default: -a -b -c
if in options_config it's taken as -abc
+<letters> $ my_cmd +abc unpacking is the default: +a +b +c
if in options_config it's taken as +abc
-<letters>=<value> $ my_cmd -name=Foo (default)
+<letters>=<value> $ my_cmd +name=Foo (default)
--<letters> $ my_cmd --list (default)
--<letters>=<value> $ my_cmd --message=Bar (default)
--<letters> <value> $ my_cmd --message Bar options_config needs a type entry saying it expects a value (other than bool)
-- $ my_cmd -- --param-anyway parameters delimiter
(default)

<letters> means [a-zA-Z] and '-'s not in the first place

An argument like '-a*' gets unpacked if...

  • '-a' is not defined to expect a value
  • the '*' part has only letters, not '-' or '='

How to change the interpretation of -swing

It can mean (default):
-s -w -i -n -g
or
-s wing / -s=wing
To acheve the latter make the parser aware that '-s' expects a str value:

options_config = [
    ('-s', str),
]

Make the parser aware that an option expects a value after a space

Add type explicitly in options_config.
For just getting as it is add str.

How to define option types

Use build-in types like int or float, or create a callable that raises exceptions.
Using bool is a special case: parser will not expect a value but explicitly adds an error if one provided.

How to add empty value to an option

--option= Some commands support '-' as empty value like curl -C - -O http://domanin.com/
To avoid ambiguities this syntax is not supported.
Use --option= instead.

How to define options

options_test.py:

from quickparse import QuickParse

options_config = [
    ('-u', '--utc', '--universal'),
    ('-l', '--long'),
    ('-n', '--name', str),
]

quickparse = QuickParse(options_config=options_config)

print(f'quickparse.options: {quickparse.options}')
print(f'quickparse.errors: {quickparse.errors}')

Run it:

$ python options_test.py
quickparse.options: {}
quickparse.errors: {}

$ python options_test.py -u
quickparse.options: {'-u': True, '--utc': True, '--universal': True}
quickparse.errors: {}

$ python options_test.py -ul
quickparse.options: {'-u': True, '--utc': True, '--universal': True, '-l': True, '--long': True}
quickparse.errors: {}

$ python options_test.py -uln
quickparse.options: {'-u': True, '--utc': True, '--universal': True, '-l': True, '--long': True, '-n': True, '--name': True}
quickparse.errors: {'-n': {'type': 1, 'message': "No value got for '-n/--name' - validator: str"}, '--name': {'type': 1, 'message': "No value got for '-n/--name' - validator: str"}}

$ python options_test.py -ul -nthe_name
quickparse.options: {'-u': True, '--utc': True, '--universal': True, '-l': True, '--long': True, '-n': 'the_name', '--name': 'the_name'}
quickparse.errors: {}

$ python options_test.py -ul -n the_name
quickparse.options: {'-u': True, '--utc': True, '--universal': True, '-l': True, '--long': True, '-n': 'the_name', '--name': 'the_name'}
quickparse.errors: {}

$ python options_test.py -ul -n=the_name
quickparse.options: {'-u': True, '--utc': True, '--universal': True, '-l': True, '--long': True, '-n': 'the_name', '--name': 'the_name'}
quickparse.errors: {}

$ python options_test.py -ul --name the_name
quickparse.options: {'-u': True, '--utc': True, '--universal': True, '-l': True, '--long': True, '--name': 'the_name', '-n': 'the_name'}
quickparse.errors: {}

$ python options_test.py -ul --name=the_name
quickparse.options: {'-u': True, '--utc': True, '--universal': True, '-l': True, '--long': True, '--name': 'the_name', '-n': 'the_name'}
quickparse.errors: {}

Test your command line arguments

quickparse_test_args.py (committed in the repo):

from pprint import pformat

from quickparse import QuickParse


def do_show_help():
    print("Executing 'do_show_help'...")

def do_commit():
    print("Executing 'do_commit'...")

def do_log(quickparse):
    print("Executing 'do_log'...")

def do_stash():
    print("Executing 'do_stash'...")

def do_stash_list():
    print("Executing 'do_stash_list'...")

commands_config = {
    '': do_show_help,
    'commit': do_commit,
    'log': do_log,
    'stash': {
        '': do_stash,
        'list': do_stash_list,
    }
}

options_config = [
    ('-m', '--message', str),
    ('-p', '--patch'),
]


quickparse = QuickParse(commands_config, options_config)


print(f'Commands:\n{pformat(quickparse.commands)}')
print(f'Parameters:\n{pformat(quickparse.parameters)}')
print(f'Options:\n{pformat(quickparse.options)}')
print(f'\'-\' numeric argument:\n{pformat(quickparse.numeric)}')
print(f'\'+\' numeric argument:\n{pformat(quickparse.plusnumeric)}')
print(f'Functions to call:\n{pformat(quickparse.to_execute)}')

quickparse.execute()

Error handling

If the parser parameters 'commands_config' or 'options_config' are not valid, ValueError is rased from the underlying AssertionError.
If the arguments are not compliant with the config (e.g. no value provided for an option that requires one) then no exceptions are raised but an errors list is populated on the QuickParse object.

See the error object again from options_test.py

$ python options_test.py -uln
quickparse.options: {'-u': True, '--utc': True, '--universal': True, '-l': True, '--long': True, '-n': True, '--name': True}
quickparse.errors: {'-n': {'type': 1, 'message': "No value got for '-n/--name' - validator: str"}, '--name': {'type': 1, 'message': "No value got for '-n/--name' - validator: str"}}

quickparse.errors dict is about validation of options. These are the types:

ERROR_TYPE_VALIDATION = 0
ERROR_VALUE_NOT_FOUND = 1
ERROR_INCOMPLETE_COMMAND = 2

quickparse.has_errors is also available to check if any errors occurred.

Validation

Well, I still need to elaborate the docs on this but here is a quick example snippet.

quickparse.validate({
    'parameters': { 'mincount': 1, },
    'options': {
        'mandatory': '--branch',
        'optional': '--stage',
    },
    'numeric': { 'maxcount': 0 },
    'plusnumeric': { 'maxcount': 0 },
})
assert 'parameters.mincount' not in quickparse.errors, f'Add a target'
assert not quickparse.has_errors, '\n'.join(quickparse.error_messages)

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