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Application configuration engine

Project description

Tweak is a Python helper class to ingest and serialize app-specific configuration.

Tweak provides a self-contained (no dependencies outside the standard library), Python 2 and 3 compatible configuration manager. It automatically saves and restores your application’s configuration in your user home directory. It uses JSON or (optionally) YAML for serialization. It supports dict-like methods and access semantics, hierarchical configuration sources, and array merge operators for layering configuration options (see below).


If your package does not permit dependency management, you can copy the Config class directly into your application from Otherwise:

pip install tweak


from tweak import Config

config = Config(), config.port = "", 9000
config.nested_config = {} = True

After restarting your application:

config = Config()
>>> {'host': '', 'port': 9000, 'nested_config': {'foo': True}}

Using an argparse.Namespace object returned by argparse.parse_args():

parser = argparse.ArgumentParser()
args = parser.parse_args()
if is not None: =
elif "foo" not in config:
    raise Exception("foo unconfigured")


Using YAML:

config = Config(use_yaml=True)

Pass Config(save_on_exit=False) to disable automatic configuration saving on Python shutdown (this is useful if you only want to read the config, never write it, or if you want to call manually). Pass Config(autosave=True) to make save() run any time an assignment happens to a config object.

Configuration ingestion order

Tweak supports ingesting configuration from a configurable array of sources. Each source is a JSON or YAML file. Configuration sources that follow the first source update the configuration using recursive dictionary merging. Sources are enumerated in the following order:

  • Site-wide configuration source, /etc/NAME/config.(yml|json)
  • User configuration source, ~/.config/NAME/config.(yml|json)
  • Any sources listed in the colon-delimited variable NAME_CONFIG_FILE

Array merge operators

When loading a chain of configuration sources, Tweak uses recursive dictionary merging to combine the sources. Additionally, when the original config value is a list, Tweak supports array manipulation operators:

In [1]: from tweak import Config

In [2]: c = Config()

In [3]: c.update(x=[1, 2, 3])

In [4]: c
Out[4]: {'x': [1, 2, 3]}

In [5]: c.update(x={"$append": 4})

In [6]: c
Out[6]: {'x': [1, 2, 3, 4]}

In [7]: c.update(x={"$extend": [5, 6]})

In [8]: c
Out[8]: {'x': [1, 2, 3, 4, 5, 6]}

In [9]: c.update(x={"$insert": {0: 0}})

In [10]: c
Out[10]: {'x': [0, 1, 2, 3, 4, 5, 6]}

In [11]: c.update(x={"$extendleft": [-2, -1]})

In [12]: c
Out[12]: {'x': [-2, -1, 0, 1, 2, 3, 4, 5, 6]}

In [13]: c.update(x={"$remove": 0})

In [14]: c
Out[14]: {'x': [-2, -1, 1, 2, 3, 4, 5, 6]}

Each operator ($append, $extend, $insert, $extendleft, $remove) must be the only key in the dictionary representing the update, and the value being updated must be a list. For example, in the following set of two YAML files, the second file extends the list in the first file.


 - y
 - z


   - a
   - b

Include directives

The optional Config(allow_includes=True) keyword argument can be used to trigger processing of include directives in config files. For each config source file ingested, a top level include key can contain a string or array of strings. Each of these strings will be globbed and ingested before the file contianing the directive (e.g. {"include": "config.d/*"} to ingest a directory of config files).


  • Andrey Kislyuk


Licensed under the terms of the Apache License, Version 2.0.

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