A custom YAML tag for referencing environment variables in YAML files.
A custom YAML tag for referencing environment variables in YAML files.
Install PyYAML
and the pyyaml_env_tag
package with pip:
pip install pyyaml pyyaml_env_tag
To enable the tag, import and add the construct_env_tag
constructor to your YAML
loader of choice.
import yaml
from yaml_env_tag import construct_env_tag
yaml.Loader.add_constructor('!ENV', construct_env_tag)
Then you may use the loader as per usual. For example:
yaml.load(data, Loader=yaml.Loader)
Include the tag !ENV
followed by the name of an environment variable in a YAML
file and the value of the environment variable will be used in its place.
key: !ENV SOME_VARIABLE
If SOME_VARIABLE
is set to A string!
, then the above YAML would result in the
following Python object:
{'key': 'A string!'}
The content of the variable is parsed using YAML's implicit scalar types, such as
string, bool, integer, float, datestamp and null. More complex types are not
recognized and simply passed through as a string. For example, if SOME_VARIABLE
was set to the string true
, then the above YAML would result in the following:
{'key': True}
If the variable specified is not set, then a null
value is assigned as a default.
You may define your own default as the last item in a sequence.
key: !ENV [SOME_VARIABLE, default]
In the above example, if SOME_VARIABLE
is not defined, the string default
would
be used instead, as follows:
{'key': 'default'}
You may list multiple variables as fallbacks. The first variable which is set is used. In any sequance with more than one item, the last item must always be a default value and will not be resolved as an environment variable.
key: !ENV [SOME_VARIABLE, FALLBACK, default]
As with variable contents, the default is resolved to a Python object of the implied type (string, bool, integer, float, datestamp and null).
When SOME_VARIABLE
is not set, all four of the following items will resolve to
the same value (None
):
- !ENV SOME_VARIABLE
- !ENV [SOME_VARIABLE]
- !ENV [SOME_VARIABLE, ~]
- !ENV [SOME_VARIABLE, null]
pyyaml_env_tag was inspired by the Ruby package yaml-env-tag.
An alternate method of referencing environment variables in YAML files is implemented by pyyaml-tags and python_yaml_environment_variables. Each of those libraries use a template string and replace the template tag with the content of the variable. While this allows a single value to reference multiple variables and to contain additional content, it restricts all values to strings only and does not provide a way to define defaults.
pyyaml_env_tag is licensed under the MIT License as defined in LICENSE
.
The initial release.