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Description:

argclass 1.0.3

argclass

A wrapper around the standard argparse module that allows you to describe
argument parsers declaratively.
By default, the argparse module suggests creating parsers imperative,
which is not convenient from the point of view of type checking and
access to attributes, of course, IDE autocompletion and type hints not
applicable in this case.
This module allows you to declare command-line parsers with classes.
Simple example:

import logging
import argclass

class CopyParser(argclass.Parser):
recursive: bool
preserve_attributes: bool

parser = CopyParser()
parser.parse_args(["--recursive", "--preserve-attributes"])
assert parser.recursive
assert parser.preserve_attributes

As you can see this example shown a basic module usage, when you want specify
argument default and other options you have to use argclass.Argument.
Following example use argclass.Argument and argument groups:

from typing import FrozenSet
import logging
import argclass

class AddressPortGroup(argclass.Group):
address: str = argclass.Argument(default="127.0.0.1")
port: int

class Parser(argclass.Parser):
log_level: int = argclass.LogLevel
http = AddressPortGroup(title="HTTP options", defaults=dict(port=8080))
rpc = AddressPortGroup(title="RPC options", defaults=dict(port=9090))
user_id: FrozenSet[int] = argclass.Argument(
nargs="*", type=int, converter=frozenset
)

parser = Parser(
config_files=[".example.ini", "~/.example.ini", "/etc/example.ini"],
auto_env_var_prefix="EXAMPLE_"
)
parser.parse_args([])

# Remove all used environment variables from os.environ
parser.sanitize_env()

logging.basicConfig(level=parser.log_level)
logging.info('Listening http://%s:%d', parser.http.address, parser.http.port)
logging.info(f'Listening rpc://%s:%d', parser.rpc.address, parser.rpc.port)

assert parser.http.address == '127.0.0.1'
assert parser.rpc.address == '127.0.0.1'

assert parser.http.port == 8080
assert parser.rpc.port == 9090

Run this script:
$ python example.py
INFO:root:Listening http://127.0.0.1:8080
INFO:root:Listening rpc://127.0.0.1:9090

Example of --help output:
$ python example.py --help
usage: example.py [-h] [--log-level {debug,info,warning,error,critical}]
[--http-address HTTP_ADDRESS] [--http-port HTTP_PORT]
[--rpc-address RPC_ADDRESS] [--rpc-port RPC_PORT]

optional arguments:
-h, --help show this help message and exit
--log-level {debug,info,warning,error,critical}
(default: info) [ENV: EXAMPLE_LOG_LEVEL]

HTTP options:
--http-address HTTP_ADDRESS
(default: 127.0.0.1) [ENV: EXAMPLE_HTTP_ADDRESS]
--http-port HTTP_PORT
(default: 8080) [ENV: EXAMPLE_HTTP_PORT]

RPC options:
--rpc-address RPC_ADDRESS
(default: 127.0.0.1) [ENV: EXAMPLE_RPC_ADDRESS]
--rpc-port RPC_PORT (default: 9090) [ENV: EXAMPLE_RPC_PORT]

Default values will based on following configuration files ['example.ini',
'~/.example.ini', '/etc/example.ini']. Now 1 files has been applied
['example.ini']. The configuration files is INI-formatted files where
configuration groups is INI sections.
See more https://pypi.org/project/argclass/#configs

Secrets
Arguments reflecting some sensitive data, tokens or encryption keys,
urls with passwords, when passed through environment variables or a
configuration file, can be printed in the output of --help.
To hide defaults, add the secret=True parameter,
or use the special default constructor argclass.Secret instead of
argclass.Argument.
import argclass

class HttpAuthentication(argclass.Group):
username: str = argclass.Argument()
password: str = argclass.Secret()

class HttpBearerAuthentication(argclass.Group):
token: str = argclass.Argument(secret=True)

class Parser(argclass.Parser):
http_basic = HttpAuthentication()
http_bearer = HttpBearerAuthentication()

parser = Parser()
parser.print_help()

Trying to protect data from being written to the log
A secret is not actually a string, but a special class inherited
from a str, and all attempts to cast this type to a str
(using __str__ method) should be fine, and returning the original
value, unless the __str__ method call is from a logging module.
>>> import logging
>>> from argclass import SecretString
>>> logging.basicConfig(level=logging.INFO)
>>> s = SecretString("my-secret-password")
>>> logging.info(s) # __str__ will be called from logging
>>> logging.info(f"s=%s", s) # __str__ will be called from logging too
>>> logging.info(f"{s!r}") # repr is safe
>>> logging.info(f"{s}") # the password will be compromised

Of course this is not a absolute sensitive data protection,
but I hope it helps against accidental logging of this kind of values.
The repr for this will always give placeholder, so it is better to always
add !r for any f-string, for example f'{value!r}'.
Configs
The parser objects might be get default values from environment variables or
one of passed configuration files.
import argclass

class AddressPortGroup(argclass.Group):
address: str = argclass.Argument(default="127.0.0.1")
port: int

class Parser(argclass.Parser):
spam: str
quantity: int
log_level: int = argclass.LogLevel
http = AddressPortGroup(title="HTTP options")
rpc = AddressPortGroup(title="RPC options")
user_ids = argclass.Argument(
type=int, converter=frozenset, nargs=argclass.Nargs.ONE_OR_MORE
)

# Trying to parse all passed configuration files
# and break after first success.
parser = Parser(
config_files=[".example.ini", "~/.example.ini", "/etc/example.ini"],
)
parser.parse_args()

In this case each passed and existent configuration file will be opened.
The root level arguments might be described in the [DEFAULT] section.
Other arguments might be described in group specific sections.
So the full example of config file for above example is:
[DEFAULT]
log_level=info
spam=egg
quantity=100
user_ids=[1, 2, 3]

[http]
address=127.0.0.1
port=8080

[rpc]
address=127.0.0.1
port=9090

Enum argument

import enum
import logging
import argclass

class LogLevelEnum(enum.IntEnum):
debug = logging.DEBUG
info = logging.INFO
warning = logging.WARNING
error = logging.ERROR
critical = logging.CRITICAL

class Parser(argclass.Parser):
"""Log level with default"""
log_level = argclass.EnumArgument(LogLevelEnum, default="info")

class ParserLogLevelIsRequired(argclass.Parser):
log_level: LogLevelEnum

parser = Parser()
parser.parse_args([])
assert parser.log_level == logging.INFO

parser = Parser()
parser.parse_args(["--log-level=error"])
assert parser.log_level == logging.ERROR

parser = ParserLogLevelIsRequired()
parser.parse_args(["--log-level=warning"])
assert parser.log_level == logging.WARNING

Config Action
This library provides base class for writing custom configuration parsers.
YAML parser
from typing import Mapping, Any
from pathlib import Path

import argclass
import yaml

class YAMLConfigAction(argclass.ConfigAction):
def parse_file(self, file: Path) -> Mapping[str, Any]:
with file.open("r") as fp:
return yaml.load_all(fp)

class YAMLConfigArgument(argclass.ConfigArgument):
action = YAMLConfigAction

class Parser(argclass.Parser):
config = argclass.Config(
required=True,
config_class=YAMLConfigArgument,
)

TOML parser
import tomli
import argclass
from pathlib import Path
from typing import Mapping, Any

class TOMLConfigAction(argclass.ConfigAction):
def parse_file(self, file: Path) -> Mapping[str, Any]:
with file.open("r") as fp:
return tomli.load(fp)

class TOMLConfigArgument(argclass.ConfigArgument):
action = TOMLConfigAction

class Parser(argclass.Parser):
config = argclass.Config(
required=True,
config_class=TOMLConfigArgument,
)

Subparsers
There are two ways to work with subparsers: either by calling the parser as a regular function, and in this case,
the subparser must implement the __call__ method, otherwise help will be printed and the program will exit with
an error. Or you can directly look at the .current_subparser attribute in the parser. The second method seems
more complicated, but it becomes less difficult if you use singledispatch from the standard library.
Using __call__
Just implement __call__ method for subparsers and call
from typing import Optional

import argclass

class AddressPortGroup(argclass.Group):
address: str = "127.0.0.1"
port: int = 8080

class CommitCommand(argclass.Parser):
comment: str = argclass.Argument()

def __call__(self):
endpoint: AddressPortGroup = self.__parent__.endpoint
print(
"Commit command called", self,
"endpoint", endpoint.address, "port", endpoint.port
)

class PushCommand(argclass.Parser):
comment: str = argclass.Argument()

def __call__(self):
endpoint: AddressPortGroup = self.__parent__.endpoint
print(
"Push command called", self,
"endpoint", endpoint.address, "port", endpoint.port
)

class Parser(argclass.Parser):
log_level: int = argclass.LogLevel
endpoint = AddressPortGroup(title="Endpoint options")
commit: Optional[CommitCommand] = CommitCommand()
push: Optional[PushCommand] = PushCommand()

parser = Parser(
config_files=["example.ini", "~/.example.ini", "/etc/example.ini"],
auto_env_var_prefix="EXAMPLE_"
)
parser.parse_args()
parser()

Using singledispatch
Complex example with subparsers:
from functools import singledispatch
from typing import Optional, Any

import argclass

class AddressPortGroup(argclass.Group):
address: str = argclass.Argument(default="127.0.0.1")
port: int

class CommitCommand(argclass.Parser):
comment: str = argclass.Argument()

class PushCommand(argclass.Parser):
comment: str = argclass.Argument()

class Parser(argclass.Parser):
log_level: int = argclass.LogLevel
endpoint = AddressPortGroup(
title="Endpoint options",
defaults=dict(port=8080)
)
commit: Optional[CommitCommand] = CommitCommand()
push: Optional[PushCommand] = PushCommand()

@singledispatch
def handle_subparser(subparser: Any) -> None:
raise NotImplementedError(
f"Unexpected subparser type {subparser.__class__!r}"
)

@handle_subparser.register(type(None))
def handle_none(_: None) -> None:
Parser().print_help()
exit(2)

@handle_subparser.register(CommitCommand)
def handle_commit(subparser: CommitCommand) -> None:
print("Commit command called", subparser)

@handle_subparser.register(PushCommand)
def handle_push(subparser: PushCommand) -> None:
print("Push command called", subparser)

parser = Parser(
config_files=["example.ini", "~/.example.ini", "/etc/example.ini"],
auto_env_var_prefix="EXAMPLE_"
)
parser.parse_args()
handle_subparser(parser.current_subparser)

Value conversion
If the argument has a generic or composite type, then you must explicitly
describe it using argclass.Argument, while specifying the converter
function with type or converter argument to transform the value
after parsing the arguments.
The exception to this rule is Optional with a single type. In this case,
an argument without a default value will not be required,
and its value can be None.

import argclass
from typing import Optional, Union

def converter(value: str) -> Optional[Union[int, str, bool]]:
if value.lower() == "none":
return None
if value.isdigit():
return int(value)
if value.lower() in ("yes", "true", "enabled", "enable", "on"):
return True
return False

class Parser(argclass.Parser):
gizmo: Optional[Union[int, str, bool]] = argclass.Argument(
converter=converter
)
optional: Optional[int]

parser = Parser()

parser.parse_args(["--gizmo=65535"])
assert parser.gizmo == 65535

parser.parse_args(["--gizmo=None"])
assert parser.gizmo is None

parser.parse_args(["--gizmo=on"])
assert parser.gizmo is True
assert parser.optional is None

parser.parse_args(["--gizmo=off", "--optional=10"])
assert parser.gizmo is False
assert parser.optional == 10