climatecontrol 0.7.3.post1

Python library for loading app configurations from files and/or namespaced environment variables

CLIMATECONTROL

CLIMATECONTROL controls your apps configuration environment. It is a Python library for loading app configurations from files and/or namespaced environment variables.

Install

pip install climatecontrol

Usage

Set some environment variables in your shell

export MY_APP_VALUE1=test1
export MY_APP_VALUE2=test2

Then use them in your python modules:

from climatecontrol.settings_parser import Settings
settings_map = Settings(prefix='MY_APP')
print(dict(settings_map))

{
    'value1': 'test1',
    'value2': 'test2'
}

In case you want to update your settings or your environment variables have changed and you want to reload them, the update method will reload your settings:

import os
os.environ['MY_APP_VALUE3'] = 'new_env_data'
settings_map.update()
print(dict(settings_map))

{
    'value1': 'test1',
    'value2': 'test2',
    'value3': 'new_env_data'
}

Now you’ve noticed that you want more complex configurations and need nested settings. For this situation we can delimit sections using a double underscore:

export MY_APP_SECTION1__VALUE1=test1
export MY_APP_SECTION2__VALUE2=test2
export MY_APP_SECTION2__VALUE3=test3
export MY_APP_SECTION2__SUB_SECTION__VALUE4=test4

settings_map = Settings(prefix='MY_APP')
print(dict(settings_map))

{
    'section1': {
        'value1': 'test1'
    },
    'section2': {
        'value2': 'test2',
        'value3': 'test3',
        'sub_section': {
            'value4': 'test4'
        }
    }
}

Finally if you decide that your settings are simpler and you know that your section names do not have underscores, you can use the implicit_depth option, which allows you to add a new section at every single underscore (up to the depth you specify).

export MY_APP_SECTION1_VALUE1=test1
export MY_APP_SECTION2_VALUE2=test2
export MY_APP_SECTION2_VALUE3=test3
export MY_APP_SECTION2_SUBSECTION_VALUE4=test4

settings_map = Settings(prefix='MY_APP', implicit_depth=2)
print(dict(settings_map))

{
    'section1': {
        'value1': 'test1'
    },
    'section2': {
        'value2': 'test2',
        'value3': 'test3',
        'subsection': {
            'value4': 'test4'
        }
    }
}

Settings file support

If you don’t want to use an environment variable for every single setting and want to put your settings in a single file instead you can to this as well. Settings files can be yaml files (.yml/ .yaml), json files (.json) or toml files (.toml).

export MY_APP_SETTINGS_FILE=./my_settings_file.yml

The file could look like this:

section1:
  subsection1 = test1

section2:
  subsection2: test2
  subsection3: test3

or in toml form:

export MY_APP_SETTINGS_FILE=./my_settings_file.toml

[section1]
subsection1 = "test1"

[section2]
subsection2 = "test2"
subsection3 = "test3"

In the following documentation examples, yaml files will be used, but any examples will work using the other file syntaxes as well.

Setting variables whos values are saved in files

Sometimes we don’t want to save values in plain text in environment files or in the settings file itself. Instead we have a file that contains the value of the setting we want. A good example for this behaviour are docker secrets that store secrets in temporary files.

To read a variable from a file, simply add a “_from_file” to the variable name and give it the path to the file that contains the variable as a value.

Using a settings file with the contents (in this case yaml):

section1:
  subsection1_from_file: /home/myuser/supersecret.txt

or using an environment variable:

export MY_APP_SECTION1_SUBSECTION1_FROM_FILE="/home/myuser/supersecret.txt"

will both write the content of the file at “/home/myuser/supersecret.txt” into the variable section1 -> subsection1.

Nested settings files

In addition, file variables can also target other settings files directly. To do this, just make sure the target file is has an extension supported by climate control. A simple example is illustrated here. Given a settings file:

value1: "spam"
section1_from_file: /home/myuser/nestedfile.yaml

where the content of /home/myuser/nestedfile.yaml is:

value2: "cheese"
subsection:
  value3: "parrot"

which would result in a settings structure:

{
    "value1": "spam",
    "section1": {
        "value2": "cheese",
        "subsection": {
            "value3": "parrot"
        }
    }
}

Command line support using click

The click library is a great tool for creating command line applications. If you don’t want to have to use an environment to set your configuration file. Write your command line application like this:

import click

@click.command()
@settings_map.click_settings_file_option()
def cli():
   print(dict(settings_parser))

save it to a file like “cli.py” and then call it after installing click:

pip install click
python cli.py --settings ./my_settings_file.toml

whithout needing to set any env vars.

Multiple files are supported. They will be automatically recursively merged with the last file overriting any overlapping keys of the first file.

pip install click
python cli.py --settings ./my_settings_file.toml  --settings ./my_settings_file.yaml

Testing

When testing your application, different behaviours often depend on settings taking on different values. Assuming that you are using a single Settings object accross multiple functions or modules, handling these settings changes in tests can be tricky.

The settings object provides a simple method for modifying your settings object temporarily:

settings_map.update({'a': 1})
# Enter a temporary changes context block:
with settings_map.temporary_changes():
    settings_map.update({'a': 1})
    # Inside the context, the settings can be modified and used as you choose
    print(settings_map['a'])  # outputs: 2
# After the context exits the settings map
print(settings_map['a'])  # outputs: 1

Python version support

Do to the use of modern python features, only python 3.5 and above are supported.