## Dishka (stands for "cute DI" in Russian)

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Cute DI framework with scopes and agreeable API.

📚 [Documentation](https://dishka.readthedocs.io)

### Purpose

This library provides **IoC container** that's genuinely useful.
If you're exhausted from endlessly passing objects just to create other objects, only to have those objects create even
more — you're not alone, and we have a solution.
Not every project requires IoC container, but take a look at what we offer.

Unlike other tools, Dishka focuses **only**
on [dependency injection](https://dishka.readthedocs.io/en/latest/di_intro.html) without trying to solve unrelated
tasks.
It keeps DI in place without cluttering your code with global variables and scattered specifiers.

To see how Dishka **stands out** among other dependency injection tools, check out
the [detailed comparison](https://dishka.readthedocs.io/en/latest/alternatives.html).

#### Key features:

* **Scopes**. Any object can have a lifespan for the entire app, a single request, or even more fractionally. Many
  frameworks either lack scopes completely or offer only two. Here, you can define as many scopes as needed.
* **Finalization**. Some dependencies, like database connections, need not only to be created but also carefully
  released. Many frameworks lack this essential feature.
* **Modular providers**. Instead of creating many separate functions or one large class, you can split factories
  into smaller classes for easier reuse.
* **Clean dependencies**. You don't need to add custom markers to dependency code just to make it visible to the
  library.
* **Simple API**. Only a few objects are needed to start using the library.
* **Framework integrations**. Popular frameworks are supported out of the box. You can simply extend it for you needs.
* **Speed**. The library is fast enough that performance is not a concern. In fact, it outperforms many
  alternatives.

See more in [technical requirements.](https://dishka.readthedocs.io/en/latest/requirements/technical.html)

### Quickstart

1. **Install Dishka.**

```shell
pip install dishka
```

2. **Define your classes with type hints.** Imagine you have two classes: `Service` (business logic) and
   `DAO` (data access), along with an external API client:

```python
class DAO(Protocol):
    ...


class Service:
    def __init__(self, dao: DAO):
        ...


class DAOImpl(DAO):
    def __init__(self, connection: Connection):
        ...


class SomeClient:
    ...
```

3. **Create `Provider`** instance and specify how to provide dependencies.

Providers are used only to set up factories providing your objects.

Use `scope=Scope.APP` for dependencies created once for the entire application lifetime,
and `scope=Scope.REQUEST` for those that need to be recreated for each request, event, etc.
To learn more about scopes, see [documentation.](https://dishka.readthedocs.io/en/latest/advanced/scopes.html)

```python
from dishka import Provider, Scope


service_provider = Provider(scope=Scope.REQUEST)
service_provider.provide(Service)
service_provider.provide(DAOImpl, provides=DAO)
service_provider.provide(SomeClient, scope=Scope.APP)  # override provider scope
```

To provide a connection, you might need some custom code:

```python
from dishka import Provider, provide, Scope


class ConnectionProvider(Provider):
    @provide(scope=Scope.REQUEST)
    def new_connection(self) -> Iterable[Connection]:
        conn = sqlite3.connect(":memory:")
        yield conn
        conn.close()
```

4. **Create main `Container`** instance, passing providers, and enter `APP` scope.

```python
from dishka import make_container


container = make_container(service_provider, ConnectionProvider())
```

5. **Access dependencies using container.** Container holds a cache of dependencies and is used to retrieve them.
   You can use `.get` method to access `APP`-scoped dependencies:

```python
client = container.get(SomeClient)  # `SomeClient` has Scope.APP, so it is accessible here
client = container.get(SomeClient)  # same instance of `SomeClient`
```

6. **Enter and exit `REQUEST` scope repeatedly using a context manager**:

```python
# subcontainer to access shorter-living objects
with container() as request_container:
    service = request_container.get(Service)
    service = request_container.get(Service)  # same service instance
# since we exited the context manager, the connection is now closed

# new subcontainer to have a new lifespan for request processing
with container() as request_container:
    service = request_container.get(Service)  # new service instance
```

7. **Close container** when done:

```python
container.close()
```

8. **Integrate with your framework.** If you are using a supported framework, add decorators and middleware for it.
   For more details, see [integrations doc.](https://dishka.readthedocs.io/en/latest/integrations/index.html)

```python
from dishka.integrations.fastapi import (
    FromDishka, inject, setup_dishka,
)


@router.get("/")
@inject
async def index(service: FromDishka[Service]) -> str:
    ...


...
setup_dishka(container, app)
```

### Concepts

**Dependency** is what you need for some parts of your code to work.
Dependencies are simply objects you don't create directly in place and might want to replace someday, at least for
testing purposes.
Some of them live for the entire application lifetime, while others are created and destroyed with each request.
Dependencies can also rely on other objects, which then become their dependencies.

**Scope** is the lifespan of a dependency. Standard scopes are (with some skipped):

`APP` -> `REQUEST` -> `ACTION` -> `STEP`.

You decide when to enter and exit each scope, but this is done one by one.
You set a scope for each dependency when you configure how it is created.
If the same dependency is requested multiple times within a single scope without leaving it, then by default the same
instance is returned.

For a web application, enter `APP` scope on startup and `REQUEST` scope for each HTTP request.

You can create a custom scope by defining your own `Scope` class if the standard scope flow doesn't fit your needs.

**Container** is what you use to get your dependencies.
You simply call `.get(SomeType)` and it finds a way to provide you with an instance of that type.
Container itself doesn't create objects but manages their lifecycle and caches.
It delegates object creation to providers that are passed during creation.

**Provider** is a collection of functions that provide concrete objects.
`Provider` is a class with attributes and methods, each being the result of `provide`, `alias`, `from_context`, or
`decorate`.
They can be used as provider methods, functions to assign attributes, or method decorators.

`@provide` can be used as a decorator for a method.
This method will be called when the corresponding dependency has to be created.
Name doesn't matter: just make sure it's different from other `Provider` attributes.
Type hints do matter: they indicate what this method creates and what it requires.
All method parameters are treated as dependencies and are created using the container.

If `provide` is applied to a class, that class itself is treated as a factory (its `__init__` parameters are analyzed).
Remember to assign this call to an attribute; otherwise, it will be ignored.

**Component** is an isolated group of providers within the same container, identified by a unique string.
When a dependency is requested, it is only searched within the same component as its direct dependant, unless explicitly
specified otherwise.

This structure allows you to build different parts of the application separately without worrying about using the same
types.
