env-proxy 1.3.0

Creates a class used to query environmental variables with typehinting a conversion to basic Python types.

EnvProxy

EnvProxy is a Python package that provides a convenient proxy for accessing environment variables with type hints, type conversion, and customizable options for key formatting. It alos includes EnvConfig, which lets you define configuration classes that map directly to environment variables. With EnvConfig, you can declaratively describe your environment-based configuration, including defaults, type hints, and optional sample .env file generation.

Installation

To install EnvProxy, use standard package management tools for Python:

# Using pip
pip install env-proxy

# Using poetry
poetry add env-proxy

Usage

Basic Usage with EnvProxy

Start by creating an EnvProxy instance with optional configuration for environment variable key transformations:

from env_proxy import EnvProxy

proxy = EnvProxy(prefix="MYAPP")

The prefix option adds a prefix to all keys, allowing you to group related variables under a common namespace. For example, with prefix="MYAPP", proxy.get_any("var") will look for the environment variable MYAPP_VAR. See the Configuration Options for EnvProxy section for more options.

Retrieving Environment Variables

Each method returns the value of an environment variable, converting it to the specified type. If the variable is missing, it either raises an error or returns the provided default.

Methods

get_any

Retrieve the raw value of a variable as Any. If the key does not exist, ValueError is raised unless a default is provided.

# export MYAPP_VAR="value"

value = proxy.get_any("var")  # returns "value"

get_bool

Retrieve a boolean variable. The following values are considered truthy (case-insensitive):

yes, true, 1, on, enable, enabled, allow

Similarly, common falsy values are handled:

no, false, 0, off, disable, disabled, disallow, deny

# export MYAPP_ENABLED="true"

value = proxy.get_bool("enabled")  # returns True

get_str

Retrieve a string variable.

# export MYAPP_NAME="example"

name = proxy.get_str("name")  # returns "example"

get_int

Retrieve an integer variable.

# export MYAPP_COUNT="42"

count = proxy.get_int("count")  # returns 42

get_float

Retrieve a floating-point variable.

# export MYAPP_RATIO="3.14"

ratio = proxy.get_float("ratio")  # returns 3.14

get_list

Retrieve a list of strings by splitting the variable’s value based on a separator (default is ,).

# export MYAPP_ITEMS="a,b,c ,d"

items = proxy.get_list("items")  # returns ["a", "b", "c", "d"]

get_json

Parse a JSON string from the environment.

# export MYAPP_CONFIG='{"key": "value"}'

config = proxy.get_json("config")  # returns {"key": "value"}

EnvConfig – Declarative Configuration with Fields

The new EnvConfig class allows you to define environment-based configuration with type hints, descriptions, and defaults. It automatically connects fields to environment variables using a declarative approach, and can even generate a sample .env file for easy setup.

Defining Configuration Classes with EnvConfig

Define your configuration by subclassing EnvConfig and using Field factory to describe each variable. The Field function supports attributes like description, default, and type_hint (see Field Options).

from env_proxy import EnvConfig, Field, EnvProxy

class MyConfig(EnvConfig):
    env_proxy = EnvProxy(prefix="MYAPP")  # common prefix for all fields
    debug: bool = Field(description="Enable debug mode", default=False)
    database_url: str = Field(description="Database connection URL")
    max_connections: int = Field(description="Maximum DB connections", default=10)
    cache_backends: list[str] = Field(description="Cache backends", type_hint="list")

Accessing Config Values

Once defined, MyConfig provides easy access to each environment variable with the specified type conversions.

config = MyConfig()

# Access configuration values

debug = config.debug  # Looks for MYAPP_DEBUG in the environment
database_url = config.database_url  # Raises ValueError if not found

Overriding Values per Instance

EnvConfig accepts keyword arguments to override individual fields on a per-instance basis. Overrides take precedence over the environment, letting you layer the env-derived config with values from any other source — a config file, CLI arguments, programmatic wiring, fixtures — without touching os.environ.

class AppConfig(EnvConfig):
    env_proxy = EnvProxy(prefix="APP")
    timeout: int = Field(default=30)
    services: list[str] = Field(default=[])

# Layer env with values loaded from a config file:
file_config = load_yaml("app.yaml")  # {"timeout": 5, "services": ["redis", "rabbitmq"]}
cfg = AppConfig(**file_config)

assert cfg.timeout == 5
assert cfg.services == ["redis", "rabbitmq"]

Semantics:

• Keys are Python field names (not env-var keys), regardless of any alias or env_prefix.
• Values are used as-is — no string parsing or type conversion. Pass real int, list, dict, etc.
• Overrides shadow the environment for reads on that instance only; other instances and direct os.environ access are unaffected.
• Unknown override keys raise ValueError, listing the valid field names — typo-proof.
• Fields with allow_set=False can be initialized via override but cannot be reassigned afterwards; the allow_set contract is unchanged.
• For fields with allow_set=True, assignment after construction updates both the override entry and os.environ (preserving the existing side-effect contract).

Overrides are statically type-checked. EnvConfig is decorated with PEP 681's dataclass_transform, so mypy and Pyright/Pylance synthesize a typed __init__ from each subclass's annotated fields: typos (AppConfig(timout=5)) and wrong value types (AppConfig(timeout="bad")) are flagged at type-check time, and IDEs autocomplete field names with their declared types.

Generating a Sample .env File

You can export a sample .env file from your EnvConfig class, which documents all fields with their descriptions, types, and default values.

MyConfig.export_env("sample.env", include_defaults=True)

This would produce a file like:

# debug (bool) [optional]
# Enable debug mode
MYAPP_DEBUG=False

# database_url (str) [required]
# Database connection URL
MYAPP_DATABASE_URL=

# max_connections (int) [optional]
# Maximum DB connections
MYAPP_MAX_CONNECTIONS=10

# cache_backends (list) [required]
# Cache backends
MYAPP_CACHE_BACKENDS=

Field Options

Each Field can be customized with the following options:

• alias: Custom name in the environment. Defaults to the field name.
• description: Description of the variable.
• default: Default value if the variable is missing. If UNSET, the variable is required.
• type_hint: Specify the type explicitly (e.g., json for JSON objects).
• env_prefix: Override the env_prefix set on the EnvConfig class for a specific field.
• allow_set: Allow modification of the environment variable value at runtime.

Field Type Hints

The following type_hint values are supported:

• any
• bool
• float
• int
• str
• list
• json

Example of using type_hint:

class AdvancedConfig(EnvConfig):
    settings: dict[str, Any] = Field(type_hint="json", description="Complex JSON settings")

Example Usage with EnvConfig

import os
from env_proxy import EnvConfig, Field

# Set environment variables
os.environ["MYAPP_DEBUG"] = "true"
os.environ["MYAPP_DATABASE_URL"] = "sqlite:///data.db"
os.environ["MYAPP_CACHE_BACKENDS"] = "redis,memcached"

class MyConfig(EnvConfig):
    env_prefix: str = "MYAPP"
    debug: bool = Field(description="Enable debug mode", default=False)
    database_url: str = Field(description="Database connection URL")
    cache_backends: list[str] = Field(description="Cache backends", type_hint="list")

config = MyConfig()

# Access configuration values

print(config.debug)  # True
print(config.database_url)  # "sqlite:///data.db"
print(config.cache_backends)  # ["redis", "memcached"]

# Export a sample .env file

MyConfig.export_env("sample.env", include_defaults=True)

Configuration Options for EnvProxy

You can control how keys are transformed when retrieving variables in EnvProxy:

• prefix: Adds a prefix to all keys.
• uppercase: Converts keys to uppercase.
• underscored: Replaces hyphens with underscores.

proxy = EnvProxy(prefix="myapp", uppercase=True, underscored=False)
proxy.get_any("var")  # Looks for "MYAPP_VAR"

Error Handling

If a variable is not found, and no default value is provided, a ValueError will be raised. Each method also raises a ValueError for invalid conversions.

try:
    missing_value = proxy.get_int("missing_key")
except ValueError as e:
    print(e)  # Output: No value found for key 'missing_key' in the environment.

License

EnvProxy is open-source and distributed under the MIT License. See LICENSE.md for more information.