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Conversion of User Guide to the SHH stack (#2781)

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2023-09-06 15:44:00 +03:00
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# Sanic Application
## Instance
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The most basic building block is the `Sanic()` instance. It is not required, but the custom is to instantiate this in a file called `server.py`.
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```python
# /path/to/server.py
from sanic import Sanic
app = Sanic("MyHelloWorldApp")
```
## Application context
Most applications will have the need to share/reuse data or objects across different parts of the code base. The most common example is DB connections.
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In versions of Sanic prior to v21.3, this was commonly done by attaching an attribute to the application instance
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```python
# Raises a warning as deprecated feature in 21.3
app = Sanic("MyApp")
app.db = Database()
```
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Because this can create potential problems with name conflicts, and to be consistent with [request context](./request.md#context) objects, v21.3 introduces application level context object.
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```python
# Correct way to attach objects to the application
app = Sanic("MyApp")
app.ctx.db = Database()
```
## App Registry
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When you instantiate a Sanic instance, that can be retrieved at a later time from the Sanic app registry. This can be useful, for example, if you need to access your Sanic instance from a location where it is not otherwise accessible.
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```python
# ./path/to/server.py
from sanic import Sanic
app = Sanic("my_awesome_server")
# ./path/to/somewhere_else.py
from sanic import Sanic
app = Sanic.get_app("my_awesome_server")
```
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If you call `Sanic.get_app("non-existing")` on an app that does not exist, it will raise `SanicException` by default. You can, instead, force the method to return a new instance of Sanic with that name.
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```python
app = Sanic.get_app(
"non-existing",
force_create=True,
)
```
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If there is **only one** Sanic instance registered, then calling `Sanic.get_app()` with no arguments will return that instance
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```python
Sanic("My only app")
app = Sanic.get_app()
```
## Configuration
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Sanic holds the configuration in the `config` attribute of the `Sanic` instance. Configuration can be modified **either** using dot-notation **OR** like a dictionary.
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```python
app = Sanic('myapp')
app.config.DB_NAME = 'appdb'
app.config['DB_USER'] = 'appuser'
db_settings = {
'DB_HOST': 'localhost',
'DB_NAME': 'appdb',
'DB_USER': 'appuser'
}
app.config.update(db_settings)
```
.. note:: Heads up
Config keys _should_ be uppercase. But, this is mainly by convention, and lowercase will work most of the time.
```
app.config.GOOD = "yay!"
app.config.bad = "boo"
```
There is much [more detail about configuration](/guide/deployment/configuration.md) later on.
## Customization
The Sanic application instance can be customized for your application needs in a variety of ways at instantiation.
### Custom configuration
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This simplest form of custom configuration would be to pass your own object directly into that Sanic application instance
If you create a custom configuration object, it is *highly* recommended that you subclass the Sanic `Config` option to inherit its behavior. You could use this option for adding properties, or your own set of custom logic.
*Added in v21.6*
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```python
from sanic.config import Config
class MyConfig(Config):
FOO = "bar"
app = Sanic(..., config=MyConfig())
```
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A useful example of this feature would be if you wanted to use a config file in a form that differs from what is [supported](../deployment/configuration.md#using-sanic-update-config).
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```python
from sanic import Sanic, text
from sanic.config import Config
class TomlConfig(Config):
def __init__(self, *args, path: str, **kwargs):
super().__init__(*args, **kwargs)
with open(path, "r") as f:
self.apply(toml.load(f))
def apply(self, config):
self.update(self._to_uppercase(config))
def _to_uppercase(self, obj: Dict[str, Any]) -> Dict[str, Any]:
retval: Dict[str, Any] = {}
for key, value in obj.items():
upper_key = key.upper()
if isinstance(value, list):
retval[upper_key] = [
self._to_uppercase(item) for item in value
]
elif isinstance(value, dict):
retval[upper_key] = self._to_uppercase(value)
else:
retval[upper_key] = value
return retval
toml_config = TomlConfig(path="/path/to/config.toml")
app = Sanic(toml_config.APP_NAME, config=toml_config)
```
### Custom context
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By default, the application context is a [`SimpleNamespace()`](https://docs.python.org/3/library/types.html#types.SimpleNamespace) that allows you to set any properties you want on it. However, you also have the option of passing any object whatsoever instead.
*Added in v21.6*
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```python
app = Sanic(..., ctx=1)
```
```python
app = Sanic(..., ctx={})
```
```python
class MyContext:
...
app = Sanic(..., ctx=MyContext())
```
### Custom requests
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It is sometimes helpful to have your own `Request` class, and tell Sanic to use that instead of the default. One example is if you wanted to modify the default `request.id` generator.
.. note:: Important
It is important to remember that you are passing the *class* not an instance of the class.
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```python
import time
from sanic import Request, Sanic, text
class NanoSecondRequest(Request):
@classmethod
def generate_id(*_):
return time.time_ns()
app = Sanic(..., request_class=NanoSecondRequest)
@app.get("/")
async def handler(request):
return text(str(request.id))
```
### Custom error handler
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See [exception handling](../best-practices/exceptions.md#custom-error-handling) for more
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```python
from sanic.handlers import ErrorHandler
class CustomErrorHandler(ErrorHandler):
def default(self, request, exception):
''' handles errors that have no error handlers assigned '''
# You custom error handling logic...
return super().default(request, exception)
app = Sanic(..., error_handler=CustomErrorHandler())
```
### Custom dumps function
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It may sometimes be necessary or desirable to provide a custom function that serializes an object to JSON data.
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```python
import ujson
dumps = partial(ujson.dumps, escape_forward_slashes=False)
app = Sanic(__name__, dumps=dumps)
```
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Or, perhaps use another library or create your own.
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```python
from orjson import dumps
app = Sanic(__name__, dumps=dumps)
```
### Custom loads function
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Similar to `dumps`, you can also provide a custom function for deserializing data.
*Added in v22.9*
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```python
from orjson import loads
app = Sanic(__name__, loads=loads)
```
.. new:: NEW in v23.6
### Custom typed application
The correct, default type of a Sanic application instance is:
```python
sanic.app.Sanic[sanic.config.Config, types.SimpleNamespace]
```
It refers to two generic types:
1. The first is the type of the configuration object. It defaults to `sanic.config.Config`, but can be any subclass of that.
2. The second is the type of the application context. It defaults to `types.SimpleNamespace`, but can be **any object** as show above.
Let's look at some examples of how the type will change.
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Consider this example where we pass a custom subclass of `Config` and a custom context object.
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```python
from sanic import Sanic
from sanic.config import Config
class CustomConfig(Config):
pass
app = Sanic("test", config=CustomConfig())
reveal_type(app) # N: Revealed type is "sanic.app.Sanic[main.CustomConfig, types.SimpleNamespace]"
```
```
sanic.app.Sanic[main.CustomConfig, types.SimpleNamespace]
```
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Similarly, when passing a custom context object, the type will change to reflect that.
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```python
from sanic import Sanic
class Foo:
pass
app = Sanic("test", ctx=Foo())
reveal_type(app) # N: Revealed type is "sanic.app.Sanic[sanic.config.Config, main.Foo]"
```
```
sanic.app.Sanic[sanic.config.Config, main.Foo]
```
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Of course, you can set both the config and context to custom types.
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```python
from sanic import Sanic
from sanic.config import Config
class CustomConfig(Config):
pass
class Foo:
pass
app = Sanic("test", config=CustomConfig(), ctx=Foo())
reveal_type(app) # N: Revealed type is "sanic.app.Sanic[main.CustomConfig, main.Foo]"
```
```
sanic.app.Sanic[main.CustomConfig, main.Foo]
```
This pattern is particularly useful if you create a custom type alias for your application instance so that you can use it to annotate listeners and handlers.
```python
# ./path/to/types.py
from sanic.app import Sanic
from sanic.config import Config
from myapp.context import MyContext
from typing import TypeAlias
MyApp = TypeAlias("MyApp", Sanic[Config, MyContext])
```
```python
# ./path/to/listeners.py
from myapp.types import MyApp
def add_listeners(app: MyApp):
@app.before_server_start
async def before_server_start(app: MyApp):
# do something with your fully typed app instance
await app.ctx.db.connect()
```
```python
# ./path/to/server.py
from myapp.types import MyApp
from myapp.context import MyContext
from myapp.config import MyConfig
from myapp.listeners import add_listeners
app = Sanic("myapp", config=MyConfig(), ctx=MyContext())
add_listeners(app)
```
*Added in v23.6*
### Custom typed request
Sanic also allows you to customize the type of the request object. This is useful if you want to add custom properties to the request object, or be able to access your custom properties of a typed application instance.
The correct, default type of a Sanic request instance is:
```python
sanic.request.Request[
sanic.app.Sanic[sanic.config.Config, types.SimpleNamespace],
types.SimpleNamespace
]
```
It refers to two generic types:
1. The first is the type of the application instance. It defaults to `sanic.app.Sanic[sanic.config.Config, types.SimpleNamespace]`, but can be any subclass of that.
2. The second is the type of the request context. It defaults to `types.SimpleNamespace`, but can be **any object** as show above in [custom requests](#custom-requests).
Let's look at some examples of how the type will change.
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Expanding upon the full example above where there is a type alias for a customized application instance, we can also create a custom request type so that we can access those same type annotations.
Of course, you do not need type aliases for this to work. We are only showing them here to cut down on the amount of code shown.
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```python
from sanic import Request
from myapp.types import MyApp
from types import SimpleNamespace
def add_routes(app: MyApp):
@app.get("/")
async def handler(request: Request[MyApp, SimpleNamespace]):
# do something with your fully typed app instance
results = await request.app.ctx.db.query("SELECT * FROM foo")
```
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Perhaps you have a custom request object that generates a custom context object. You can type annotate it to properly access those properties with your IDE as shown here.
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```python
from sanic import Request, Sanic
from sanic.config import Config
class CustomConfig(Config):
pass
class Foo:
pass
class RequestContext:
foo: Foo
class CustomRequest(Request[Sanic[CustomConfig, Foo], RequestContext]):
@staticmethod
def make_context() -> RequestContext:
ctx = RequestContext()
ctx.foo = Foo()
return ctx
app = Sanic(
"test", config=CustomConfig(), ctx=Foo(), request_class=CustomRequest
)
@app.get("/")
async def handler(request: CustomRequest):
# Full access to typed:
# - custom application configuration object
# - custom application context object
# - custom request context object
pass
```
See more information in the [custom request context](./request.md#custom-request-context) section.
*Added in v23.6*