Typed, extensible, dependency free configuration reader for Python projects for multiple config sources and working well in IDEs for great autocomplete performance.
Project description
typed-config
Typed, extensible, dependency free configuration reader for Python projects for multiple config sources and working well in IDEs for great autocomplete performance.
pip install typed-config
Requires python 3.6 or above.
Basic usage
# my_app/config.py
from typedconfig import Config, key, section
from typedconfig.source import EnvironmentConfigSource
@section('database')
class AppConfig(Config):
host = key(cast=str)
port = key(cast=int)
timeout = key(cast=float)
config = AppConfig()
config.add_source(EnvironmentConfigSource())
config.read()
# my_app/main.py
from my_app.config import config
print(config.host)
In PyCharm, and hopefully other IDEs, it will recognise the datatypes of your configuration and allow you to autocomplete. No more remembering strings to get the right thing out!
How it works
Configuration is always supplied in a two level structure, so your source configuration can have multiple sections, and each section contains multiple key/value configuration pairs. For example:
[database]
host = 127.0.0.1
port = 2000
[algorithm]
max_value = 10
min_value = 20
You then create your configuration hierarchy in code (this can be flat or many levels deep) and supply the matching between strings in your config sources and properties of your configuration classes.
You provide one or more ConfigSource
s, from which the config for your application can be read. For example, you might supply an EnvironmentConfigSource
, and two IniFileConfigSource
s. This would make your application first look for a configuration value in environment variables, if not found there it would then look at the first INI file (perhaps a user-specific file), before falling back to the second INI file (perhaps a default configuration shared between all users). If a parameter is still not found and is a required parameter, an error would be thrown.
There is emphasis on type information being available for everything so that an IDE will autocomplete when trying to use your config across your application.
Multiple data sources
from typedconfig import Config, key, section, group_key
from typedconfig.source import EnvironmentConfigSource, IniFileConfigSource
@section('database')
class DatabaseConfig(Config):
host = key(cast=str)
port = key(cast=int)
username = key(cast=str)
password = key(cast=str)
config = DatabaseConfig()
config.add_source(EnvironmentConfigSource(prefix="EXAMPLE"))
config.add_source(IniFileConfigSource("config.cfg"))
# OR provide sources directly to the constructor
config = DatabaseConfig(sources=[
EnvironmentConfigSource(prefix="EXAMPLE"),
IniFileConfigSource("config.cfg")
])
Since you don't want to hard code your secret credentials, you might supply them through the environment. So for the above configuration, the environment might look like this:
export EXAMPLE_DATABASE_USERNAME=my_username
export EXAMPLE_DATABASE_PASSWORD=my_very_secret_password
export EXAMPLE_DATABASE_PORT=2001
Those values which couldn't be found in the environment would then be read from the INI file, which might look like this:
[database]
HOST = db1.mydomain.com
PORT = 2000
Note after this, config.port
will be equal to 2001
as the value in the environment took priority over the value in the INI file.
Caching
When config values are first used, they are read. This is lazy evaluation by default so that not everything is read if not necessary.
After first use, they are cached in memory so that there should be no further I/O if the config value is used again.
For fail fast behaviour, and also to stop unexpected latency when a config value is read partway through your application (e.g. your config could be coming across a network), the option is available to read all config values at the start. Just call
config.read()
This will throw an exception if any required config value cannot be found, and will also keep all read config values in memory for next time they are used. If you do not use read
you will only get the exception when you first try to use the offending config key.
Hierarchical configuration
Use group_key
to represent a "sub-config" of a configuration. Set up "sub-configs" exactly as demonstrated above, and then create a parent config to compose them in one place.
from typedconfig import Config, key, section, group_key
from typedconfig.source import EnvironmentConfigSource, IniFileConfigSource
@section('database')
class DatabaseConfig(Config):
host = key(cast=str)
port = key(cast=int)
@section('algorithm')
class AlgorithmConfig(Config):
max_value = key(cast=float)
min_value = key(cast=float)
class ParentConfig(Config):
database = group_key(DatabaseConfig)
algorithm = group_key(AlgorithmConfig)
description = key(cast=str, section_name="general")
config = ParentConfig()
config.add_source(EnvironmentConfigSource(prefix="EXAMPLE"))
config.add_source(IniFileConfigSource("config.cfg"))
config.read()
The first time the config.database
or config.algorithm
is accessed (which in the case above is when read()
is called), then an instance will be instantiated. Notice that it is the class definition, not an instance of the class, which is passed to the group_key
function.
Custom section/key names, optional parameters, default values
Let's take a look at this:
from typedconfig import Config, key, section
@section('database')
class AppConfig(Config):
host1 = key()
host2 = key(section_name='database', key_name='HOST2',
required=True, cast=str, default=None)
Both host1
and host2
are legitimate configuration key definitions.
section_name
- this name of the section in the configuration source from which this parameter should be read. This can be provided on a key-by-key basis, but if it is left out then the section name supplied by the@section
decorator is used. If all keys supply asection_name
, the class decorator is not needed. If bothsection_name
and a decorator are provided, thesection_name
argument takes priority.key_name
- the name of this key in the configuration source from which this parameter is read. If not supplied, some magic uses the object property name as the key name.required
- default True. If False, and the configuration value can't be found, no error will be thrown and the default value will be used, if provided. If a default not provided,None
will be used.cast
- probably the most important option for typing. If you want autocomplete typing support you must specify this. It's just a function which takes a string as an input and returns a parsed value. See the casting section for more. If not supplied, the value remains as a string.default
- only applicable ifrequired
is false. Whenrequired
is false this value is used if a value cannot be found.
Types
from typedconfig import Config, key, section
from typing import List
def split_str(s: str) -> List[str]:
return [x.strip() for x in s.split(",")]
@section('database')
class AppConfig(Config):
host = key()
port = key(cast=int)
users = key(cast=split_str)
zero_based_index = key(cast=lambda x: int(x)-1)
config = AppConfig(sources=[...])
In this example we have three ways of casting:
- Not casting at all. This default to returning a
str
, but your IDE won't know that so if you want type hints usecast=str
- Casting to an built in type which can take a string input and parse it, for example
int
- Defining a custom function. Your function should take one string input and return one output of any type. To get type hint, just make sure your function has type annotations.
- Using a lambda expression. The type inference may or may not work depending on your expression, so if it doesn't just write it as a function with type annotations.
Configuration Sources
Configuration sources are how your main Config
class knows where to get its data from. These are totally extensible so that you can read in your configuration from wherever you like - from a database, from S3, anywhere that you can write code for.
You supply your configuration source to your config after you've instantiated it, but before you try to read any data from it:
config = AppConfig()
config.add_source(my_first_source)
config.add_source(my_second_source)
config.read()
Or you can supply the sources directly in the constructor like this:
config = AppConfig(sources=[my_first_source, my_second_source])
config.read()
The below is bad practice, but if for some reason you do add further config sources after it's been read, or need to refresh the config for some reason, you'll need to clear any cached values in order to force re-reading of the config. You can do this by
config.clear_cache()
config.read() # Read all configuration values again
Supplied Config Sources
EnvironmentConfigSource
This just reads configuration from environment variables.
from typedconfig.source import EnvironmentConfigSource
source = EnvironmentConfigSource(prefix="XYZ")
# OR just
source = EnvironmentConfigSource()
It just takes one optional input argument, a prefix. This can be useful to avoid name clashes in environment variables.
- If prefix is provided, environment variables are expected to look like
{PREFIX}_{SECTION}_{KEY}
, for exampleexport XYZ_DATABASE_PORT=2000
. - If no prefix is provided, environment variables should look like
{SECTION}_{KEY}
, for exampleexport DATABASE_PORT=2000
.
IniFileConfigSource
This reads from an INI file using Python's built in configparser. Read the docs for configparser
for more about the structure of the file.
from typedconfig.source import IniFileConfigSource
source = IniFileConfigSource("config.cfg", encoding='utf-8', must_exist=True)
- The first argument is the filename (absolute or relative to the current working directory).
encoding
is the text encoding of the file.configparser
's default is used if not supplied.must_exist
- defaultTrue
. If the file can't be found, an error will be thrown by default. Settingmust_exist
to beFalse
allows the file not to be present, in which case this source will just report that it can't find any configuration values and yourConfig
class will move onto looking in the nextConfigSource
.
IniStringConfigSource
This reads from a string instead of a file
from typedconfig.source import IniStringConfigSource
source = IniStringConfigSource("""
[section_name]
key_name=key_value
""")
DictConfigSource
The most basic source, entirely in memory, and also useful when writing tests. It is case insensitive.
from typedconfig.source import DictConfigSource
source = DictConfigSource({
'database': dict(HOST='db1', PORT='2000'),
'algorithm': dict(MAX_VALUE='20', MIN_VALUE='10')
})
It expects data type Dict[str, Dict[str, str]]
, i.e. such that string_value = d['section_name']['key_name']
. Everything should be provided as string data so that it can be parsed in the same way as if data was coming from a file or elsewhere.
This is an alternative way of supplying default values instead of using the default
option when defining your key
s. Just provide a DictConfigSource
as the lowest priority source, containing your defaults.
Writing your own ConfigSource
s
An abstract base class ConfigSource
is supplied. You should extend it and implement the method get_config_value
as demonstrated below, which takes a section name and key name, and returns either a str
config value, or None
if the value could not be found. It should not error if the value cannot be found, Config
will throw an error later if it still can't find the value in any of its other available sources. To make it easier for the user try to make your source case insensitive.
Here's an outline of how you might implement a source to read your config from a JSON file, for example. Use the __init__
method to provide any information your source needs to fetch the data, such as filename, api details, etc. You can do sanity checks in the __init__
method and throw an error if something is wrong.
import json
from typing import Optional
from typedconfig.source import ConfigSource
class JsonConfigSource(ConfigSource):
def __init__(self, filename: str):
# Read data - will raise an exception if problem with file
with open(filename, 'r') as f:
self.data = json.load(f)
# Quick checks on data format
assert type(self.data) is dict
for k, v in self.data.items():
assert type(k) is str
assert type(v) is dict
for v_k, v_v in v.items():
assert type(v_k) is str
assert type(v_v) is str
# Convert all keys to lowercase
self.data = {
k.lower(): {
v_k.lower(): v_v
for v_k, v_v in v.items()
}
for k, v in self.data.items()
}
def get_config_value(self, section_name: str, key_name: str) -> Optional[str]:
# Extract info from data which we read in during __init__
section = self.data.get(section_name.lower(), None)
if section is None:
return None
return section.get(key_name.lower(), None)
Additional config sources
In order to keep typed-config
dependency free, ConfigSources
requiring additional dependencies are in separate packages, which also have typed-config
as a dependency.
These are listed here:
pip install name | import name | Description |
---|---|---|
typed-config-aws-sources | typedconfig_awssource |
Config sources using boto3 to get config e.g. from S3 or DynamoDB |
Contributing
Ideas for new features and pull requests are welcome. PRs must come with tests included. This was developed using Python 3.7 but Travis tests run with v3.6 too.
Development setup
- Clone the git repository
- Create a virtual environment
virtualenv venv
- Activate the environment
venv/scripts/activate
- Install development dependencies
pip install -r requirements.txt
Running tests
pytest
To run with coverage:
pytest --cov
Making a release
You'll need to pip install twine
if you don't have it.
- Bump version number in
typedconfig/__version__.py
- Add changes to CHANGELOG.md
- Commit your changes and tag with
git tag -a v0.1.0 -m "Summary of changes"
- Clear the dist directory
rm -r dist
python setup.py sdist bdist_wheel
twine check dist/*
- Upload to the test PyPI
twine upload --repository-url https://test.pypi.org/legacy/ dist/*
- Check all looks ok at https://test.pypi.org/project/typed-config
- Upload to live PyPI
twine upload dist/*
Here is a good tutorial on publishing packages to PyPI.
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