Easily model and convert environment variables you care about.
Project description
e2e.env
Class-based modeling of environment variables and their type conversions.
Especially suited to test automation where environment variables are used in abundance, or even in applications that could benefit from these mappings.
Requirements
For ease of implementation, Python 3.6 is required in order to use PEP-526 variable annotations.
Overview
Environment variable access is common, and usually done via a module-based approach.
SERVICE_HOST = os.getenv('COMPANY_APP_HOST')
SERVICE_PORT = int(os.getenv('COMPANY_APP_PORT'))
This works just fine, but sometimes they need to be refreshed...
# Whoops, forgot the int conversion!
SERVICE_PORT = os.getenv('COMPANY_APP_PORT')
... which isn't very DRY.
Additionally, you may sometimes need to keep track of the name and the value from the environment,
# This is getting verbose quickly
ENVNAME_SERVICE_HOST = 'COMPANY_APP_HOST'
SERVICE_HOST = os.getenv(ENVNAME_SERVICE_HOST)
ENVNAME_SERVICE_PORT = 'COMPANY_APP_PORT'
SERVICE_PORT = int(os.getenv(ENVNAME_SERVICE_PORT))
In one swoop, we can map the environment variables as well as their conversions to native types, and fetch either the value or the name:
class ServiceVars(e2e.env.EnvMapper):
host: str = 'COMPANY_APP_HOST'
port: int = 'COMPANY_APP_PORT'
# Get the port via instance
print(ServiceVars().port) # 8080
type(ServiceVars().port) # <class 'int'>
# Get the name of the port environment variable via class
print(ServiceVars.port) # COMPANY_APP_PORT
type(ServiceVars.port) # <class 'str'>
Using your own "converters"
All EnvMapper
does is read the type annotation and constructs the returned
value by passing the environment value to it.
That is, when modeling,
mapped_name: annotated_type = 'ENV_VAR_NAME'
... on access via the EnvMapper
instance, becomes ...
annotated_type(os.getenv('ENV_VAR_NAME'))
In the above examples for example, we had port: int = 'COMPANY_APP_PORT'
.
This essentially gets shuffled into int(os.getenv('COMPANY_APP_PORT'))
. So
any callable that can take a single str
in its constructor and return the
appropriate type will work.
Production use
The code is incredibly simple, and will adhere to these contracts:
- Variables that do not exist will cause a
e2e.env.exceptions.NoSuchVariableError
to be raised.* - Access of an unmapped environment variable will raise an
AttributeError
, as would be reasonably expected. - Access of a mapping without an annotation will raise a
TypeError
with the mapping name and model class.
* Open for discussion. Returning None
could work. Passing None
to the type
converter usually won't produce consistent behaviour across types, and so can't
be determined as a special case (e.g. str(None)
gives "None"
, int(None)
raises a TypeError
). See
Issue #1 for more info.
Future work
- Support
raise_on_dne
or something similar to change what happens when an environment variable is not found. Please add a thumbs-up for Issue #1 if you'd like to see this feature.class ServiceVars(e2e.env.EnvMapper, raise_on_dne=False): ...
class ServiceVars(e2e.env.EnvMapper, dne=lambda: None): ...
- Support for combining mappings into one larger mapping, for organizational purposes. Please add a thumbs-up for Issue #2 if you'd like to see this feature.
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