hazrakah (הזרקה) is a tiny but powerful DI library for Python.

This README is only a high-level introduction to hazrakah. For more detailed documentation, please view the official docs at https://hazrakah.readthedocs.io.

Features

• Supports Singleton, Transient, and Instance lifetimes.
• Hierarchical scoping; Isolate registrations and/or resolves. optionally use a context manager to deterministically tear down a scope and its resolved objects.
• Namespaced Registrations; Register types into named scopes and resolve with priority chains. Allows multiple implementations of the same interface to coexist.
• Protocols, ABCs, and Concretes can be registered against Factory Functions and Concretes.
• Lifetime Decorators; (OPTIONAL) Types decorated with @singleton, @transient or @instanced can be registered with a single call to register_decorated(), simplifying orchestration.
• Implicit Multi-Registration; Types decorated with @provides bind to all provided types (unless explicit types are specified during registration.)
• Fluent API; All registration methods return self, enabling method-chained container setup.

Installation

You can install hazrakah from PyPI through usual means, such as pip:

   pip install hazrakah

Usage

Core lifetimes — Transient, Singleton, Instance

hazrakah manages object lifecycles through three registration strategies:

from hazrakah import Container

container = Container()

# TRANSIENT — a new instance for every resolve.
container.register_transient(IFoo, Foo)
assert container.resolve(IFoo) is not container.resolve(IFoo)

# SINGLETON — one shared instance across all resolves in scope.
container.register_singleton(IFooBar, lambda c: c.resolve(FooBarImpl))
assert container.resolve(IFooBar) is container.resolve(IFooBar)

# INSTANCE — your exact object, returned everywhere (including child scopes).
bar_obj = Bar()
container.register_instance(IBar, bar_obj)
assert container.resolve(IBar) is bar_obj

Hierarchical scopes

Scopes provide isolation: parent registrations flow down, but child-only registrations stay local.

parent = Container()
child = parent.create_scope()

parent.register_transient(IFoo, Foo)
child.resolve(IFoo)          # resolves parent's registration

child.register_transient(IBar, Bar)
child.resolve(IBar)          # works — registered in this scope
# parent.resolve(IBar)      # raises KeyError — invisible to parent

Context manager cleanup

Resolve tracked resources and get deterministic teardown when the scope exits.

from hazrakah import Container

class Closeable:
    def __init__(self): self.closed = False
    def close(self): self.closed = True

with Container() as c:
    c.register_transient(Closeable)
    res = c.resolve(Closeable)

assert res.closed               # teardown ran automatically on __exit__

Fluent chaining

All registration methods return self, enabling method-chained setup.

container = (
    Container()
    .register_transient(IFoo, Foo)
    .register_singleton(IBar, Bar)
    .register_instance(IFizz, Fizz())
)

assert isinstance(container.resolve(IFoo), Foo)
assert isinstance(container.resolve(IBar), Bar)

Caching with Cached[T]

The Cached[T] class wraps a factory callable so its result is produced once and re-used until the TTL window elapses. The factory receives a resolver argument, matching hazrakah's standard factory contract (see :py:data:hazrakah.DependencyRegistry.Factory). Register it with any container lifetime to combine DI resolution with time-bound caching:

from datetime import timedelta
from hazrakah import Container, Cached

class ConfigSource:
    def load(self) -> str:
        return 'loaded'

# TTL accepts float (seconds) or timedelta; default is 47.0 seconds.
cache = Cached(lambda c: ConfigSource(), ttl=timedelta(seconds=47))

first = cache(object())   # factory called once (TTL not yet elapsed)
second = cache(object())  # cached value returned; factory not re-invoked
assert first is second     # same instance

Every Cached instance exposes a ttl read-only property and a reset() method for manual cache eviction:

cache = Cached(lambda c: ConfigSource(), ttl=timedelta(seconds=0))
# Zero TTL — factory called on every access.
assert cache(object()) is not cache(object())  # two distinct instances
cache.reset()  # discard cached value
_ = cache(object())  # re-invokes factory

You can also pass ttl as a plain float (seconds):

cache = Cached(lambda c: ConfigSource(), ttl=120.0)  # 120 seconds
assert cache.ttl == timedelta(seconds=120)

Declarative lifetime decorators

Mark intent at class-definition time with @singleton, @transient, or @instanced, then register everything in one call.

from hazrakah import Container, singleton, transient, instanced

@singleton(types=IFoo)
class FooService: ...

@transient(types=IBar)
class BarService: ...

@instanced  # binds to the class itself
class BuzzService: ...

c = Container()
c.register_decorated()            # discovers all decorated classes

assert c.resolve(IFoo) is c.resolve(IFoo)     # singleton
assert c.resolve(IBar) is not c.resolve(IBar)  # transient

Implicit multi-registration with @provides

Declare which interfaces a class implements; registration binds to all of them simultaneously.

from hazrakah import Container, provides

@provides(IFoo, IBar)
class MultiImpl:
    def foo(self): ...
    def bar(self): ...

c = Container()
c.register_transient(MultiImpl)    # registers under IFoo, IBar, and MultiImpl

a = c.resolve(IFoo)
b = c.resolve(IBar)
assert a is b                       # same cached singleton instance

How @provides works

The @provides decorator is a passive marker -- it stores metadata only, with zero registration logic at decoration time. Activation depends entirely on how the container later registers the decorated class.

@provides activates when you call register_singleton, register_transient, or register_instance with no second argument (no explicit type override):

@provides(IFoo, IBar)
class MultiImpl: ...

c.register_singleton(MultiImpl)  # multi-registers under IFoo + IBar + MultiImpl
c.resolve(IFoo)                  # works -- @provides activated
c.resolve(IBar)                  # works -- @provides activated

@provides does NOT activate when you provide an explicit type argument to a registration method:

@provides(IBar)
class MultiImpl: ...

c.register_singleton(IFoo, MultiImpl)  # only IFoo is registered
c.resolve(IFoo)                        # works -- explicit registration
c.resolve(IBar)                        # raises KeyError -- @provides was ignored

This is intentional. The second positional argument on any register_* method is the explicit type override. When you provide it, you are telling the container exactly which key to register against -- and @provides does not interfere.

Registration call	@provides activates?	Registered keys
register_singleton(MyClass)	YES	MyClass + all @provides interfaces
register_singleton(IFoo, MyClass)	NO	Only IFoo
register_transient(MyClass)	YES	MyClass + all @provides interfaces
register_transient(IFoo, MyClass)	NO	Only IFoo
register_instance(my_obj) (no explicit instance)	YES	type(obj) + all @provides interfaces
register_instance(IFoo, my_obj) (explicit instance)	NO	Only IFoo

Contact

You can reach me on Discord or open an Issue on Github.