YAML config file -> command line interface
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Takes a YAML config file and builds a parser for command line arguments around it. This allows you to easily override default settings by passing command line arguments to your program. Supports nested arguments and auto-enforces parameter types.

This config file...

input_dir: data
    file: output.log
    level: 4

... together with this main.py ...

import yaml
import quickargs

with open("config.yaml") as f:
    config = yaml.load(f, Loader=quickargs.YAMLArgsLoader)

... will give you this command line interface

usage: main.py [-h] [--input_dir INPUT_DIR] [--logging.file LOGGING.FILE]
               [--logging.level LOGGING.LEVEL]

optional arguments:
  -h, --help            show this help message and exit
  --input_dir INPUT_DIR
                        default: data
  --logging.file LOGGING.FILE
                        default: output.log
  --logging.level LOGGING.LEVEL
                        default: 4

Override settings using the command line

python main.py --logging.file=other_log.txt

You get your merged yaml + command line parameters in a convenient dictionary

# exact same output format as normal yaml.load would produce
{'input_dir': 'data', 'logging': {'file': 'other_log.txt', 'level': 4}}

The types used in the yaml file are automatically enforced

Setting the log-level to a string instead of an int: python main.py --logging.level=WARNING
usage: main.py [-h] [--input_dir INPUT_DIR] [--logging.file LOGGING.FILE]
               [--logging.level LOGGING.LEVEL]
main.py: error: argument --logging.level: invalid int value: 'WARNING'
Setting the log-level to the correct type: python main.py --logging.level=0
{'input_dir': 'data', 'logging': {'file': 'output.log', 'level': 0}}


pip install quickargs


Load the yaml config and parse command line arguments

import yaml
import quickargs

with open("config.yaml") as f:
    config = yaml.load(f, Loader=quickargs.YAMLArgsLoader)

Deeply nested arguments are no problem

      key4: value
Override nested argument using dot notation: python main.py --key1.key2.key3.key4=other_value
{'key1': {'key2': {'key3': {'key4': 'other_value'}}}}

Of course it is fine to just call your program without any command line arguments

Happy with the default values in config file: python main.py
{'key1': {'key2': {'key3': {'key4': 'value'}}}}

Most yaml types, including sequences are supported

thresholds: [0.2, 0.4, 0.6, 0.8, 1.0]
Override the thresholds: python main.py --thresholds='[0.0, 0.5, 1.0]'

(take care to use ' ' around your command line arguments if they include spaces)

{'thresholds': [0.0, 0.5, 1.0]}

However, types within sequences are not enforced

thresholds: [0.2, 0.4, 0.6, 0.8, 1.0]
List of strings instead of list of floats does not give an error: python main.py --thresholds=[a,b,c]
{'thresholds': ['a', 'b', 'c']}

You can even pass references to functions or classes (your own or builtins)

function_to_call: !!python/name:yaml.dump
Override with reference to built-in zip function: python main.py --function_to_call=zip
{'function_to_call': <built-in function zip>}

Example with all supported types

an_int: 3
a_float: 3.0
a_bool: True
a_complex_number: 37-880j

a_date: 2016-12-11

  a_list: [a, b, c]
  # for tuples you need to use square [] brackeds in the yaml and on the command line
  # they will still be proper tuples in the result
  a_tuple: !!python/tuple [a, b]

  a_function: !!python/name:yaml.load
  a_class: !!python/name:yaml.loader.Loader
  a_module: !!python/module:contextlib
  # can be overwritten with any type
  a_none: !!python/none
Override every single parameter in the config file
python main.py --an_int=4 --a_float=2.0 --a_bool=False --a_complex_number=42-111j --a_date=2017-01-01 \
               --sequences.a_list=[c,b,c] --sequences.a_tuple=[b,a] --python.a_function=zip \
               --python.a_class=yaml.parser.Parser --python.a_module=yaml --python.a_none=1234
{'a_bool': False,
 'a_complex_number': '42-111j',
 'a_date': datetime.date(2017, 1, 1),
 'a_float': 2.0,
 'an_int': 4,
 'python': {'a_class': <class 'yaml.parser.Parser'>,
            'a_function': <built-in function zip>,
            'a_module': <module 'yaml' from ...>,
            'a_none': None},
 'sequences': {'a_list': ['c', 'b', 'c'], 'a_tuple': ('b', 'a')}}

Currently not supported


Following types are not supported at all:

  • !!python/dict (because it looks just like the rest of the yaml file)
  • !!pairs

Following types are not enforced / objects will not be instantiated:

  • !!python/object
  • !!python/object/new
  • !!python/object/apply

Multi-document loading

If the YAML file contains multiple documents, only the first document will be considered. The yaml.load_all functionality is not supported.