Declarative Parser
Modern, declarative argument parser for Python 3.6+. Powerful like click, integrated like argparse, declarative as sqlalchemy. MIT licenced. Documented on RTD. Install with:
python3 -m pip install declarative_parserAs simple as argparse
It's built on top of argparse - everything you already know stays valid!
from declarative_parser import Parser, Argument
class MyParser(Parser):
square = Argument(help='display a square of a given number')
parser = MyParser()
args = parser.parse_args()
print(args.square**2)Nested and Parallel
Everyone knows about nested args. What about parallel groups?
supported_formats = ['png', 'jpeg', 'gif']
class InputOptions(Parser):
path = Argument(type=argparse.FileType('rb'), optional=False)
format = Argument(default='png', choices=supported_formats)
class OutputOptions(Parser):
format = Argument(default='jpeg', choices=supported_formats)
scale = Argument(type=int, default=100, help='Rescale image to %% of original size')
class ImageConverter(Parser):
description = 'This app converts images'
verbose = Argument(action='store_true')
input = InputOptions()
output = OutputOptions()
parser = ImageConverter()
commands = '--verbose input image.png output --format gif --scale 50'.split()
namespace = parser.parse_args(commands)
assert namespace.input.format == 'png'
assert namespace.output.format == 'gif'Intelligent
Make use of Python 3 type hints to reduce tedious task of parsers writing to two or three lines.
Positional, keyword arguments, type hints, docstrings - everything can be meaningfully transformed into a parser.
And if you decide to take control, just overwrite the automatically deduced arguments with an Argument() defined as a class variable.
import argparse
from declarative_parser import Argument
from declarative_parser.constructor_parser import ConstructorParser
class MyProgram:
database = Argument(
type=argparse.FileType('r'),
help='Path to file with the database'
)
def __init__(self, text: str, threshold: float=0.05, database=None):
"""My program does XYZ.
Arguments:
threshold: a floating-point value defining threshold, default 0.05
database: file object to the database if any
"""
print(text, threshold, None)
parser = ConstructorParser(MyProgram)
options = parser.parse_args()
program = parser.constructor(**vars(options))And it works quite intuitively:
$ ./my_program.py test --threshold 0.6
test 0.6 None
$ ./my_program.py test --threshold f
usage: my_program.py [-h] [--database DATABASE] [--threshold THRESHOLD] text {} ...
my_program.py: error: argument --threshold: invalid float value: 'f'
$ ./my_program.py --threshold 0.6
usage: my_program.py [-h] [--database DATABASE] [--threshold THRESHOLD] text {} ...
my_program.py: error: the following arguments are required: textThree docstring formats are supported: Google, NumPy and reStructuredText, with the default being Google.
PS. It works with functions too; see the documentation of FunctionParser.
Practical
What if you only want to show licence of your program? or version? Is there a need to write a separate logic?
DeclarativeParser gives you utility decorator: @action which utilizes the power of argparse.Action,
leaving behind the otherwise necessary boilerplate code.
__version__ = 2.0
import argparse
from declarative_parser import action
from declarative_parser.constructor_parser import ConstructorParser
class MyProgram:
def __init__(self, threshold: float=0.05):
"""My program does XYZ.
Arguments:
threshold: a floating-point value, default 0.05
"""
pass
@action
def version(options):
print(__version__)
parser = ConstructorParser(MyProgram)
options = parser.parse_args()
program = parser.constructor(**vars(options))The execution of an action will (by default) cause the program to exit immediately when finished.
See following run as example:
$ ./my_program.py --version
2.0See more examples in the documentation.