castenv

castenv is a smart environment loader with robust casting/normalization, that uses python-decouple (if installed), python-dotenv with a Fallback to os.environ

current_version = "v0.3.0"

1. python-decouple (if installed)
2. python-dotenv (if installed; auto-discovers .env, .env.local, .env.{env}, .env.{env}.local across cwd+parents)
3. Fallback to os.environ

No per-call config — just castenv.get_env("KEY"), like os.environ.get but smarter.

Quick start

Install

pip install castenv
# Optional extras:
pip install "castenv[dotenv]"
pip install "castenv[decouple]"

Example

import castenv as env

# Optional one-time setup (else: auto cwd+parents):
# env.configure(search_dirs=[BASE_DIR], env_name="prod")

DATABASE_URL = env.get_env("DATABASE_URL", None)
DEBUG = env.env_bool("DEBUG", False)
DEBUG2 = env.get_env("DEBUG2", True)
TIMEOUT_SECS = env.get_env("TIMEOUT", "1m30s")  # -> seconds float (90.0)
TIMEOUT_HOURS = env.get_env("HOURS", "2d1h")  # -> seconds float (176400.0)
CACHE_BYTES = env.get_env("CACHE", "256MB")     # -> bytes int (256000000)
ALLOWED = env.get_env(
    "ALLOWED_HOSTS",
    "localhost,127.0.0.1",
    normalize_kwargs={"parse_lists": True}
)
PORT   = env.get_env("PORT", 8080)     # -> 8080 (int)
OPTS   = env.get_env("OPTS", {"x": 1}) # -> {"x": 1} (dict)
SCALE = env.get_env("SCALE", "50%", normalize_kwargs={"percent_mode": "fraction"})
TAX   = env.get_env("PORT", 15.5)     # -> 15.5 (float)

print("DATABASE_URL:", DATABASE_URL)
print("DEBUG (bool) [env_bool]:", DEBUG)
print("DEBUG2 (bool) [get_env]:", DEBUG2)
print("TIMEOUT (secs):", TIMEOUT_SECS)
print("TIMEOUT_HOURS (secs):", TIMEOUT_HOURS)
print("CACHE (bytes):", CACHE_BYTES)
print("ALLOWED_HOSTS (list):", ALLOWED)
print("PORT (int):", PORT)
print("OPTS (dict):", OPTS)
print("SCALE (float) [0-1]:", SCALE)
print("TAX (float):", TAX)

API Reference

Main Functions

get_env(key, default=None, *, normalize_kwargs=None)

Retrieves and normalizes an environment variable with automatic type casting.

Parameters:

• key (str): Environment variable name
• default (Any): Default value if key not found (default: None)
• normalize_kwargs (dict, optional): Additional normalization options (see below)

Returns: Normalized value based on content and settings

env_bool(key, default=None, **kwargs)

Retrieves environment variable as boolean.

Boolean values recognized:

• True: "true", "yes", "y", "on", "1"
• False: "false", "no", "n", "off", "0"

env_int(key, default=None, **kwargs)

Retrieves environment variable as integer.

env_float(key, default=None, **kwargs)

Retrieves environment variable as float.

env_str(key, default=None, **kwargs)

Retrieves environment variable as string.

env_list(key, default=None, *, separators=(",",), **kwargs)

Retrieves environment variable as list with custom separators.

Parameters:

• separators: Tuple of separator strings (default: (",",))

get_all(keys, defaults=None, *, normalize_kwargs=None)

Retrieves multiple environment variables at once.

Parameters:

• keys: Iterable of key names
• defaults: Dict of default values per key
• normalize_kwargs: Normalization options for all keys

normalize_config(obj, **normalize_kwargs)

Recursively normalizes config structures (dicts, lists, strings) with environment variable expansion and automatic type casting.

This is useful for loading structured config from environment variables, where you want:

1. Full support for ${VAR}, ${VAR:-default}, and $VAR environment variable references
2. Layered source precedence (decouple → dotenv → os.environ) for all variable lookups
3. Automatic type casting of expanded strings (booleans, numbers, JSON, durations, etc.)
4. Recursive processing of nested dicts and lists

Parameters:

• obj (Any): The object to process (dict, list, string, or other type)
• **kwargs: All normalization options from normalize() (see Normalization Parameters below)

Returns: The same structure with env vars expanded and types automatically cast

Key Differences from os.path.expandvars():

• Respects castenv's configured dotenv search and precedence rules
• Supports python-decouple if installed
• Handles missing variables gracefully (returns empty string by default, or uses ${VAR:-default} syntax for defaults)

Example:

import os
import castenv as env

# Set environment variables
os.environ['DB_HOST'] = 'localhost'
os.environ['DB_PORT'] = '5432'
os.environ['DB_DEBUG'] = 'true'
os.environ['ALLOWED_HOSTS'] = 'localhost,127.0.0.1,192.168.1.1'
os.environ['TIMEOUTS'] = '30s,60s,120s'

config = {
    "database": {
        "host": "${DB_HOST}",
        "port": "${DB_PORT}",
        "debug": "${DB_DEBUG}",
        "max_connections": "${MAX_CONNECTIONS:-100}",  # Uses default if not set
    },
    "hosts": "${ALLOWED_HOSTS}",
    "timeouts": "${TIMEOUTS}",
}

result = env.normalize_config(config)
# Returns:
# {
#     "database": {
#         "host": "localhost",
#         "port": 5432,              # int (not string)
#         "debug": True,             # bool (not string)
#         "max_connections": 100,    # int (from default)
#     },
#     "hosts": ["localhost", "127.0.0.1", "192.168.1.1"],  # list
#     "timeouts": [30.0, 60.0, 120.0],  # list of floats (seconds)
# }

Normalization & Casting

Automatic Type Detection

castenv automatically detects and converts values based on their content:

1. None/Null Values

Converts to Python None:

• Empty string: ""
• Null literals: "null", "none", "nil", "undefined"

env.get_env("MISSING", "")  # -> None (if coerce_empty_to_none=True)
env.get_env("NULL_VAL", "null")  # -> None

2. Boolean Conversion

Automatically detects boolean strings (case-insensitive):

True values: "true", "yes", "y", "on", "1"
False values: "false", "no", "n", "off", "0"

env.get_env("DEBUG", "true")   # -> True
env.env_bool("ENABLED", "no")  # -> False

3. Number Parsing

Integers:

• Decimal: "42" → 42
• Hexadecimal: "0xFF" → 255
• Binary: "0b1010" → 10
• Octal: "0o10" → 8

Floats:

• Standard: "3.14" → 3.14
• Scientific notation: "1e-3" → 0.001

env.get_env("HEX_COLOR", "0xFF00FF")  # -> 16711935
env.get_env("RATIO", "1.5e-2")        # -> 0.015

4. Duration Parsing

Converts human-readable durations to seconds (float):

Supported units:

• ns - nanoseconds
• us, µs - microseconds
• ms - milliseconds
• s - seconds
• m - minutes
• h - hours
• d - days
• w - weeks

Examples:

env.get_env("TIMEOUT", "1m30s")     # -> 90.0
env.get_env("CACHE_TTL", "2d1h")    # -> 176400.0
env.get_env("DELAY", "500ms")       # -> 0.5
env.get_env("WEEK", "1w")           # -> 604800.0

5. Byte Size Parsing

Converts size strings to bytes (int):

IEC Units (powers of 1024):

• b, B - bytes
• k, kb, kib, KiB - kibibytes
• m, mb, mib, MiB - mebibytes
• g, gb, gib, GiB - gibibytes
• t, tb, tib, TiB - tebibytes

SI Units (powers of 1000, uppercase trigger):

• KB - kilobytes (1000)
• MB - megabytes (1000²)
• GB - gigabytes (1000³)
• TB - terabytes (1000⁴)

env.get_env("CACHE", "256MB")       # -> 256000000 (SI: 256 * 1000²)
env.get_env("BUFFER", "1MiB")       # -> 1048576 (IEC: 1024²)
env.get_env("DISK", "500gb")        # -> 536870912000 (IEC by default)

6. Percentage Conversion

Handles percentage values with configurable output:

Modes (via percent_mode):

• "none" - Returns as string (default): "50%" → "50%"
• "number" - Returns numeric value: "50%" → 50.0
• "fraction" - Returns decimal fraction: "50%" → 0.5

env.get_env("TAX", "15%", normalize_kwargs={"percent_mode": "number"})     # -> 15.0
env.get_env("SCALE", "50%", normalize_kwargs={"percent_mode": "fraction"}) # -> 0.5
env.get_env("RAW", "25%")  # -> "25%" (default)

7. JSON Parsing

Automatically parses JSON objects and arrays:

env.get_env("CONFIG", '{"key": "value", "count": 10}')  # -> {'key': 'value', 'count': 10}
env.get_env("ITEMS", '["a", "b", "c"]')                 # -> ['a', 'b', 'c']
env.get_env("QUOTED", '"{\\"k\\": \\"v\\"}"')           # -> {'k': 'v'}

8. List Parsing

Splits comma-separated values (or custom separators) into lists:

Default separator: ,

env.get_env("HOSTS", "localhost,127.0.0.1", normalize_kwargs={"parse_lists": True})
# -> ['localhost', '127.0.0.1']

env.env_list("PORTS", "8000;8001;8002", separators=(";",))
# -> ['8000', '8001', '8002']

# Recursive normalization on list items
env.get_env("MIXED", "true,42,3.14", normalize_kwargs={"parse_lists": True})
# -> [True, 42, 3.14]

9. Environment Variable Interpolation

Expands ${VAR} and $VAR references:

# With BASE_URL="https://api.example.com"
env.get_env("API_URL", "${BASE_URL}/v1")        # -> "https://api.example.com/v1"
env.get_env("FULL_URL", "${BASE:-http://localhost}/api")  # -> Uses default if BASE not set
env.get_env("PATH", "$HOME/config")             # -> Expands $HOME

10. Path Expansion

Expands ~ to user's home directory:

env.get_env("LOG_FILE", "~/app/logs/app.log")  # -> "/home/user/app/logs/app.log"

11. Quote Handling

Strips matching quotes and unescapes common sequences:

Escape sequences supported:

• \\ → \
• \" → "
• \' → '
• \n → newline
• \r → carriage return
• \t → tab
• \b → backspace
• \f → form feed
• \0 → null byte

env.get_env("MSG", '"Hello\\nWorld"')  # -> "Hello\nWorld" (with actual newline)
env.get_env("PATH", "'C:\\\\Users\\\\App'")  # -> "C:\Users\App"

Normalization Parameters

The normalize_kwargs dictionary accepts the following parameters:

Examples with Custom Parameters

# Disable list parsing
env.get_env("CSV", "a,b,c", normalize_kwargs={"parse_lists": False})  # -> "a,b,c"

# Custom list separator
env.get_env("ITEMS", "x|y|z", normalize_kwargs={"parse_lists": True, "list_separators": ("|",)})  # -> ['x', 'y', 'z']

# Enum validation
env.get_env("ENV", "dev", normalize_kwargs={"enum": ["dev", "staging", "prod"]})  # -> "dev"
# Raises ValueError if value not in enum

# Lowercase strings
env.get_env("NAME", "MyApp", normalize_kwargs={"lowercase_strings": True})  # -> "myapp"

# Disable specific parsers
env.get_env("RAW", "true", normalize_kwargs={"parse_booleans": False})  # -> "true" (string)

Configuration

Global Configuration

Configure castenv once at startup:

from pathlib import Path
import castenv as env

env.configure(
    search_dirs=[Path("/app/config")],     # Where to look for .env files
    env_name="production",                  # Use .env.production files
    filenames=[".env", ".env.local"],       # Custom file names
    stop_at_first_found_dir=True,          # Stop at first dir with .env
    prefer_os_over_dotenv=True,            # OS env vars take precedence
    use_decouple_if_available=True         # Use python-decouple if installed
)

Temporary Configuration (Testing)

Use context manager for temporary overrides:

with env.using(search_dirs=[Path("tests/fixtures")], env_name="test"):
    # Temporary configuration active here
    value = env.get_env("TEST_VAR")
# Original configuration restored

Testing overrides

from pathlib import Path
import castenv as env

with env.using(search_dirs=[Path("tests/envs")], env_name="test"):
    assert env.get_env("SOME_KEY") == "value"

Development

Virtual Environments

python -m venv venv

Mac/Linux

source venv/bin/activate

Windows

venv/scripts/activate

Install Requirements

pip install poetry
poetry install

Install Optional Requirements

poetry install --extras "decouple"
poetry install --extras "dotenv"
poetry install --extras "decouple dotenv"

Test

pytest
coverage run -m pytest
coverage report
coverage html
mypy --html-report mypy_report .
flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics --format=html --htmldir="flake8_report/basic" --exclude=venv
flake8 . --count --exit-zero --max-complexity=11 --max-line-length=127 --statistics --format=html --htmldir="flake8_report/complexity" --exclude=venv

BumpVer

With the CLI command bumpver, you can search for and update version strings in your project files. It has a flexible pattern syntax to support many version schemes (SemVer, CalVer or otherwise). Run BumbVer with:

bumpver update --major --dry
bumpver update --major

bumpver update --minor --dry
bumpver update --minor

bumpver update --patch --dry
bumpver update --patch

Build

poetry build

Publish

poetry publish

Automated PyPI Publishing

This project uses GitHub Actions to automatically publish to PyPI when a new version tag is pushed.

Setup (One-time configuration)

1. Register a Trusted Publisher on PyPI:
   • Go to https://pypi.org/manage/account/publishing/
   • Click "Add a new pending publisher"
   • Fill in the following details:
     • PyPI Project Name: castenv
     • Owner: systemizing-solutions (your GitHub username)
     • Repository name: castenv
     • Workflow name: publish.yml
     • Environment name: pypi
   • Click "Add pending publisher"

How it works

When you use bumpver to update the version:

bumpver update --patch  # or --minor, --major

This will:

1. Update the version in pyproject.toml, src/castenv/__init__.py, and README.md
2. Create a git commit with the version bump
3. Create a git tag (e.g., 4.0.1)
4. Push the tag to GitHub

GitHub Actions will automatically detect the new tag and:

1. Build the distribution packages (wheel and source)
2. Publish to PyPI using the trusted publisher authentication

Security

This approach uses OpenID Connect (OIDC) Trusted Publishers, which is more secure than API tokens because:

• ✅ No credentials are stored in GitHub secrets
• ✅ Only this specific workflow can publish
• ✅ Only from this specific repository
• ✅ PyPI automatically verifies the request is legitimate

License

MIT