Casts¶

Loaders gather configuration from different sources, but that configuration usually is digested as strings and it might not be the correct type you need in your programs.

That’s why you can specify cast functions for each individual setting.

from classyconf import Configuration, Value, Environment, as_boolean
from decimal import Decimal


class Config(Configuration)
    class Meta:
      loaders = [Environment()]

    BASE_PRICE = Value(default=Decimal(10), cast=Decimal, help="Base product price.")
    DEBUG = Value(default=False, cast=as_boolean, help="Enables debug mode.")

Buitin Casts¶

In classyconf.casts you can find some common cast functions that ship by default. If the cast fails it will rise an InvalidConfiguration exception.

Boolean¶

Converts values like On|Off, 1|0, yes|no, y|n, true|false, t|f into booleans.

These options can be also extended by passing an extra True/False mapping.

from classyconf import Boolean

boolean = Boolean({"sim": True, "não": False})
assert boolean("sim")
assert boolean("yes")
assert not boolean("não")
assert not boolean("no")

List¶

Converts comma separated strings into lists by default.

This cast can accept other separators.

from classyconf import List

as_list = List(delimiter=";")
assert as_list("1; 2;3; ' 4; ';") == ['1', '2', '3', "' 4; '"]

Tuple¶

Same as List, but converts comma separated strings into tuples.

from classyconf import Tuple

as_tuple = Tuple()
assert as_tuple("a, b, c") == ['a', 'b', 'c']

Option¶

Gets a return value based on specific options:

from classyconf import Option

choices = {
    'option1': "asd",
    'option2': "def",
}
option = Option(choices)

assert option("option1") == "asd"
assert option("option2") == "def"

Evaluate¶

Safely evaluate strings with Python literals to Python objects (alias to Python’s ast.literal_eval).

from classyconf import evaluate

assert evaluate("None") is None

Identity¶

It is the no-op type of cast, returns anything it receives as is.

from classyconf import Identity

as_is = Identity()

assert as_is("None") is "None"

Shortcuts for standard casts¶

classyconf ships with cast instances already configured for convenience.

from classyconf import as_list, as_tuple, as_boolean, as_option, as_is, evaluate

They are pretty much self explanatory, but as_is is an instance of Identity cast.

Custom casts¶

You can implement your own custom casting function by passing any callable:

from classyconf import Configuration, Environment

def number_list(value):
    return [int(v) for v in value.split(";")]

class Config(Configuration)
    class Meta:
      loaders = [Environment()]

    NUMBERS = Value(default="1;2;3", cast=number_list, help="Semicolon separated numbers.")

Implicit casts¶

classyconf tries to provide some sensible default casts based on the default’s value type.

If the user provides a cast function, we use that one, no questions asked.
If the user sets a default that is an int, str, boolean, float, etc, and doesn’t set a cast function, we can set a default one: int(), str(), as_boolean() and float() respectively.
If the user doesn’t set a default value we use the Identity cast (as_is()).
If the user sets a non callable value as cast, we raise a TypeError exception.

So following the first example:

from classyconf import Configuration, Value, Environment
from decimal import Decimal


def number_list(value):
    return [int(v) for v in value.split(";")]


class Config(Configuration)
    class Meta:
      loaders = [Environment()]

    NUMBERS = Value("NUMBERS", default="1;2;3", cast=number_list)  # cast is number_list
    BASE_PRICE = Value(default=Decimal(10), help="Base product price.")  # cast is Decimal
    DEBUG = Value(default=False, help="Enables debug mode.")  # cast is as_boolean