envcaster 0.3.0

Typed, dependency-free environment variable loading: read env vars as int/bool/list/json/Path with defaults, required-checks, and clear errors.

envcaster ⚙️

Read environment variables as the type you actually want — int, bool, list, json, Path — with defaults, required-checks, and errors that name the offending variable. Zero dependencies, pure standard library.

os.environ only ever gives you strings. So every project grows the same little pile of int(os.environ.get("PORT", "8000")) and hand-rolled truthy checks that quietly treat "False" as True. envcaster is that pile, done once and done right.

• 🪶 Zero required dependencies — pure standard library.
• 🎯 Typed getters — str · int · float · bool · list · json · path · decimal · duration · datetime · date · bytes · url (+ custom cast).
• ✅ Built-in validation — choices, min/max bounds, and a ValidationError that's distinct from parse failures.
• 📋 Batch config checks — env.collect() reports every bad/missing variable at once, not one per restart.
• 🧯 Loud, precise errors — missing or malformed values tell you which variable and why.
• 🧪 Fully tested across Python 3.9–3.12.
• 🧩 Drop-in .env loader with optional ${VAR} interpolation — never clobbers real environment config.

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Install

pip install envcaster

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Quick start

from envcaster import env

PORT    = env.int("PORT", default=8000)
DEBUG   = env.bool("DEBUG", default=False)
HOSTS   = env.list("ALLOWED_HOSTS", sep=",")          # ["a", "b"] from "a,b"
TIMEOUT = env.float("TIMEOUT", default=1.5)
SECRET  = env.str("SECRET_KEY", required=True)         # raises if not set
DATA    = env.path("DATA_DIR", default="/var/data")   # -> pathlib.Path
FLAGS   = env.json("FEATURE_FLAGS", default={})        # parsed JSON

A variable is required unless you give it a default. Missing required variables raise MissingEnvError; bad values raise CastError. Both subclass EnvError — catch broadly or narrowly.

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Usage

Booleans that actually behave

env.bool("DEBUG")     # 1 true t yes y on  -> True   (case-insensitive)
                      # 0 false f no n off -> False
                      # anything else      -> CastError

No more bool("False") == True bugs.

Lists (and lists of other types)

env.list("ALLOWED_HOSTS")                 # "a, b ,, c" -> ["a", "b", "c"]  (trims, drops empties)
env.list("PORTS", sep=":", cast=int)      # "80:443"    -> [80, 443]
env.list("TAGS", default=[])              # missing     -> []

JSON and paths

env.json("LIMITS")          # '{"rpm": 60}' -> {"rpm": 60}
env.path("LOG_DIR")         # "/var/log"    -> PosixPath("/var/log")

Richer types — money, durations, dates, bytes, URLs

from decimal import Decimal

env.decimal("PRICE")                       # "9.99"      -> Decimal("9.99")  (exact)
env.duration("TIMEOUT")                    # "1h30m"     -> timedelta(seconds=5400)
env.duration("RETRY", default=None)        # "500ms"     -> timedelta(microseconds=500000)
env.datetime("STARTS_AT")                  # "2026-06-22T12:00:00Z" -> aware datetime (UTC)
env.date("RELEASE_DAY")                    # "2026-06-22" -> date(2026, 6, 22)
env.bytes("API_KEY", encoding="base64")    # "aGVsbG8="  -> b"hello"
env.url("WEBHOOK_URL")                     # requires scheme+host; http/https by default
env.url("REDIS_URL", schemes=["redis"])    # restrict allowed schemes

duration accepts plain seconds or ms s m h d w tokens ("30", "5m", "1h30m", "2d"). decimal/duration/datetime/date all take min/max.

Anything else — bring your own cast

from decimal import Decimal

env.cast("PRICE", Decimal)                 # "9.99" -> Decimal("9.99")
env.cast("COLOR", lambda v: int(v, 16))    # "ff0000" -> 16711680
# exceptions from your function are wrapped in CastError, naming the variable

Validate values — choices, min, max

env.str("STAGE", choices=["dev", "staging", "prod"])   # else ValidationError
env.int("PORT", min=1, max=65535)                       # range-checked
env.float("SAMPLE_RATE", min=0.0, max=1.0)
env.cast("LEVEL", str.upper, choices=["INFO", "DEBUG"]) # choices check the converted value

A value that parses but breaks a constraint raises ValidationError (a ValueError), kept distinct from CastError (which means it couldn't be parsed at all). A default you supply is trusted and never constraint-checked.

Validate a whole config at once — collect()

Stop debugging your config one missing variable per restart. collect() gathers every error in the block and raises a single report:

from envcaster import env

with env.collect() as cfg:
    PORT   = cfg.int("PORT", default=8000)
    SECRET = cfg.str("SECRET_KEY", required=True)
    DB_URL = cfg.str("DATABASE_URL", required=True)
    REGION = cfg.str("REGION", choices=["us", "eu"])

# If SECRET_KEY and DATABASE_URL are both missing, you get ONE error:
#   EnvValidationError: 2 environment variable errors found:
#     - Required environment variable 'SECRET_KEY' is not set.
#     - Required environment variable 'DATABASE_URL' is not set.

Scoped readers with a prefix

from envcaster import Env

app = Env(prefix="APP_")
app.int("PORT")        # reads APP_PORT
app.bool("DEBUG")      # reads APP_DEBUG

db = app.prefixed("DB_")   # chain prefixes
db.str("HOST")             # reads APP_DB_HOST

Read from somewhere other than os.environ

cfg = Env(source={"PORT": "9000"})   # great for tests — no global state
cfg.int("PORT")                       # 9000

Load a .env file (no dependency)

from envcaster import load_dotenv, env

load_dotenv()                  # reads ./.env into os.environ (won't override real env vars)
load_dotenv(".env.local", override=True)

PORT = env.int("PORT")

# Or parse without touching the environment:
from envcaster import read_dotenv
values = read_dotenv(".env")   # -> {"PORT": "8000", ...}

# Opt in to ${VAR} / $VAR expansion (from earlier keys, then os.environ):
read_dotenv(".env", interpolate=True)        # HOST=localhost / URL=http://${HOST} -> http://localhost

Handles KEY=value, export KEY=value, # comments, and quoted values. Single-quoted values stay literal and \$ is an escaped dollar. For multiline values, use python-dotenv.

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API reference

Call	Returns	Notes
env.str(name, default=…, required=False, choices=None)	str	The raw value, unchanged
env.int(name, …, min=None, max=None, choices=None)	int	Base-10, whitespace stripped
env.float(name, …, min=None, max=None, choices=None)	float
env.bool(name, …)	bool	1/true/t/yes/y/on ↔ 0/false/f/no/n/off
env.list(name, …, sep=",", cast=str)	list	Trims items, drops empties, per-item cast
env.json(name, …)	Any	json.loads of the value
env.path(name, …)	pathlib.Path	Not resolved/validated
env.decimal(name, …, min=None, max=None, choices=None)	Decimal	Exact precision
env.duration(name, …, min=None, max=None)	timedelta	Seconds or 500ms/5m/1h30m/2d/1w
env.datetime(name, …, min=None, max=None)	datetime	ISO 8601; trailing Z = UTC
env.date(name, …, min=None, max=None)	date	ISO 8601 YYYY-MM-DD
env.bytes(name, …, encoding="utf-8")	bytes	Codec, or base64/hex
env.url(name, …, schemes=("http","https"))	str	Validated; requires scheme + host
env.cast(name, func, …, choices=None)	Any	Apply any callable; errors wrapped in CastError
env.collect()	context manager	Batch-validate; raises one EnvValidationError
env.prefixed(prefix)	Env	New reader with a combined prefix
Env(source=None, prefix="")	Env	Custom mapping and/or name prefix
read_dotenv(path=".env", interpolate=False)	dict	Parse a .env file; {} if absent
load_dotenv(path=".env", override=False, interpolate=False)	dict	Inject into os.environ

Errors: EnvError (base) · MissingEnvError (also KeyError) · CastError (also ValueError) · ValidationError (also ValueError, for choices/min/max) · EnvValidationError (aggregate from collect()).

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Why not just os.environ?

# Before
import os
PORT  = int(os.environ.get("PORT", "8000"))
DEBUG = os.environ.get("DEBUG", "false").lower() in ("1", "true", "yes")
HOSTS = [h.strip() for h in os.environ.get("ALLOWED_HOSTS", "").split(",") if h.strip()]

# After
from envcaster import env
PORT  = env.int("PORT", default=8000)
DEBUG = env.bool("DEBUG", default=False)
HOSTS = env.list("ALLOWED_HOSTS", default=[])

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Development

git clone https://github.com/YoungAlpaccino/envcast
cd envcast
pip install -e ".[dev]"
pytest          # run tests
ruff check .    # lint

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License

MIT — see LICENSE. Use it anywhere, including commercially.