Constructors#

Three constructor-only decorators — @NoArgsConstructor, @AllArgsConstructor, and @RequiredArgsConstructor — that generate an __init__ and nothing else. They mirror Lombok’s constructor annotations, and are the right choice when you want a constructor but not the rest of what @Data provides (no repr, no eq/hash, no accessors).

The problem they solve#

Different classes want different constructor shapes: a form with no arguments (everything defaulted), a form taking every field, or a form taking only the fields that must be supplied. Writing each by hand is mechanical and easy to get out of order. These three decorators generate exactly the shape you name, deriving parameters from the class’s fields.

@AllArgsConstructor#

An __init__ taking every field — required fields first, defaulted fields after (standard Python ordering).

from inito import AllArgsConstructor


@AllArgsConstructor
class Point:
    x: int
    y: int
    label: str = "origin"


p = Point(1, 2)                 # label defaults to "origin"
q = Point(1, 2, "corner")
# __init__ signature: (self, x, y, label='origin')

@RequiredArgsConstructor#

An __init__ taking only the fields without a default. Defaulted fields are set to their default and are not constructor parameters — so the constructor asks only for what it genuinely needs.

from inito import RequiredArgsConstructor


@RequiredArgsConstructor
class Connection:
    host: str                   # required -> a parameter
    port: int                   # required -> a parameter
    timeout: float = 30.0       # has a default -> NOT a parameter


c = Connection("localhost", 5432)
print(c.timeout)                # 30.0
# __init__ signature: (self, host, port)   -- timeout is excluded

This is the closest match to Lombok’s @RequiredArgsConstructor, and pairs naturally with dependency injection: a field annotation is all @Service needs to autowire it.

@NoArgsConstructor#

An __init__ taking no arguments; every field is set to its default.

from inito import NoArgsConstructor


@NoArgsConstructor
class Settings:
    host: str = "localhost"
    port: int = 8080


s = Settings()                  # (self) -- no parameters
print(s.host, s.port)           # localhost 8080

Every field must have a default — otherwise there would be nothing to assign a required field. A field without a default raises InvalidFieldDefinitionError at decoration time (fail fast, at import), not later at construction.

At a glance#

Decorator	`__init__` parameters	Defaulted fields
`@AllArgsConstructor`	every field	become optional parameters
`@RequiredArgsConstructor`	required fields only	set to their default, not parameters
`@NoArgsConstructor`	none	set to their default (all fields must have one)

Notes & gotchas#

These generate only __init__. Add @ToString, @EqualsAndHashCode, or the accessors alongside if you want them — or just use @Data, which is @AllArgsConstructor plus all of those.
Typing: @AllArgsConstructor ships a dataclass_transform stub, so both mypy and pyright infer its __init__ signature. @NoArgsConstructor/@RequiredArgsConstructor are deliberately not marked, because dataclass_transform can’t express “zero args” or “defaulted fields excluded” without misleading the checker — enable the mypy plugin for those two.