📝 Add documentation about settings and env vars (#1118)

* Add doc and example for env var config

* Syntax highlight for .env file

* Add test for configuration docs

* 📝 Update settings docs, add more examples

* ✅ Add tests for settings

* 🚚 Rename "Application Configuration" to "Metadata and Docs URLs"

to disambiguate between that and settings

* 🔥 Remove replaced example file

Co-authored-by: Sebastián Ramírez <[email protected]>

docs/en/docs/advanced/settings.md

@@ -0,0 +1,294 @@
+# Settings and Environment Variables
+
+In many cases your application could need some external settings or configurations, for example secret keys, database credentials, credentials for email services, etc.
+
+Most of these settings are variable (can change), like database URLs. And many could be sensitive, like secrets.
+
+For this reason it's common to provide them in environment variables that are read by the application.
+
+## Environment Variables
+
+!!! tip
+    If you already know what "environment variables" are and how to use them, feel free to skip to the next section below.
+
+An <a href="https://en.wikipedia.org/wiki/Environment_variable" class="external-link" target="_blank">environment variable</a> (also known as "env var") is a variable that lives outside of the Python code, in the operating system, and could be read by your Python code (or by other programs as well).
+
+You can create and use environment variables in the shell, without needing Python:
+
+<div class="termy">
+
+```console
+// You could create an env var MY_NAME with
+$ export MY_NAME="Wade Wilson"
+
+// Then you could use it with other programs, like
+$ echo "Hello $MY_NAME"
+
+Hello Wade Wilson
+```
+
+</div>
+
+Or in PowerShell in Windows:
+
+<div class="termy">
+
+```console
+// Create an env var MY_NAME
+$ $Env:MY_NAME = "Wade Wilson"
+
+// Use it with other programs, like
+$ echo "Hello $Env:MY_NAME"
+
+Hello Wade Wilson
+```
+
+</div>
+
+### Read env vars in Python
+
+You could also create environment variables outside of Python, in the terminal (or with any other method), and then read them in Python.
+
+For example you could have a file `main.py` with:
+
+```Python hl_lines="3"
+import os
+
+name = os.getenv("MY_NAME", "World")
+print(f"Hello {name} from Python")
+```
+
+!!! tip
+    The second argument to <a href="https://docs.python.org/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> is the default value to return.
+
+    If not provided, it's `None` by default, here we provide `"World"` as the default value to use.
+
+Then you could call that Python program:
+
+<div class="termy">
+
+```console
+// Here we don't set the env var yet
+$ python main.py
+
+// As we didn't set the env var, we get the default value
+
+Hello World from Python
+
+// But if we create an environment variable first
+$ export MY_NAME="Wade Wilson"
+
+// And then call the program again
+$ python main.py
+
+// Now it can read the environment variable
+
+Hello Wade Wilson from Python
+```
+
+</div>
+
+As environment variables can be set outside of the code, but can be read by the code, and don't have to be stored (committed to `git`) with the rest of the files, it's common to use them for configurations or settings.
+
+You can also create an environment variable only for a specific program invocation, that is only available to that program, and only for its duration.
+
+To do that, create it right before the program itself, on the same line:
+
+<div class="termy">
+
+```console
+// Create an env var MY_NAME in line for this program call
+$ MY_NAME="Wade Wilson" python main.py
+
+// Now it can read the environment variable
+
+Hello Wade Wilson from Python
+
+// The env var no longer exists afterwards
+$ python main.py
+
+Hello World from Python
+```
+
+</div>
+
+!!! tip
+    You can read more about it at <a href="https://12factor.net/config" class="external-link" target="_blank">The Twelve-Factor App: Config</a>.
+
+### Types and validation
+
+These environment variables can only handle text strings, as they are external to Python and have to be compatible with other programs and the rest of the system (and even with different operating systems, as Linux, Windows, macOS).
+
+That means that any value read in Python from an environment variable will be a `str`, and any conversion to a different type or validation has be done in code.
+
+## Pydantic `Settings`
+
+Fortunately, Pydantic provides a great utility to handle these settings coming from environment variables with <a href="https://pydantic-docs.helpmanual.io/usage/settings/" class="external-link" target="_blank">Pydantic: Settings management</a>.
+
+### Create the `Settings` object
+
+Import `BaseSettings` from Pydantic and create a sub-class, very much like with a Pydantic model.
+
+The same way as with Pydantic models, you declare class attributes with type annotations, and possibly default values.
+
+You can use all the same validation features and tools you use for Pydantic models, like different data types and additional validations with `Field()`.
+
+```Python hl_lines="2  5 6 7 8  11"
+{!../../../docs_src/settings/tutorial001.py!}
+```
+
+Then, when you create an instance of that `Settings` class (in this case, in the `settings` object), Pydantic will read the environment variables in a case-insensitive way, so, an upper-case variable `APP_NAME` will still be read for the attribute `app_name`.
+
+Next it will convert and validate the data. So, when you use that `settings` object, you will have data of the types you declared (e.g. `items_per_user` will be an `int`).
+
+### Use the `settings`
+
+Then you can use the new `settings` object in your application:
+
+```Python hl_lines="18 19 20"
+{!../../../docs_src/settings/tutorial001.py!}
+```
+
+### Run the server
+
+Then you would run the server passing the configurations as environment variables, for example you could set an `ADMIN_EMAIL` and `APP_NAME` with:
+
+<div class="termy">
+
+```console
+$ ADMIN_EMAIL="[email protected]" APP_NAME="ChimichangApp" uvicorn main:app
+
+<span style="color: green;">INFO</span>:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
+```
+
+</div>
+
+!!! tip
+    To set multiple env vars for a single command just separate them with a space, and put them all before the command.
+
+And then the `admin_email` setting would be set to `"[email protected]"`.
+
+The `app_name` would be `"ChimichangApp"`.
+
+And the `items_per_user` would keep its default value of `50`.
+
+## Settings in another module
+
+You could put those settings in another module file as you saw in [Bigger Applications - Multiple Files](bigger-applications.md){.internal-link target=_blank}.
+
+For example, you could have a file `config.py` with:
+
+```Python
+{!../../../docs_src/settings/app01/config.py!}
+```
+
+And then use it in a file `main.py`:
+
+```Python hl_lines="3  11 12 13"
+{!../../../docs_src/settings/app01/main.py!}
+```
+
+!!! tip
+    You would also need a file `__init__.py` as you saw on [Bigger Applications - Multiple Files](bigger-applications.md){.internal-link target=_blank}.
+
+## Settings in a dependency
+
+In some occasions it might be useful to provide the settings from a dependency, instead of having a global object with `settings` that is used everywhere.
+
+This could be especially useful during testing, as it's very easy to override a dependency with your own custom settings.
+
+### The config file
+
+Coming from the previous example, your `config.py` file could look like:
+
+```Python hl_lines="10"
+{!../../../docs_src/settings/app02/config.py!}
+```
+
+Notice that now we don't create a default instance `settings = Settings()`.
+
+Instead we declare its type as `Settings`, but the value as `None`.
+
+### The main app file
+
+Now we create a dependency that returns the `settings` object if we already created it.
+
+Otherwise we create a new one, assign it to `config.settings` and then return it from the dependency.
+
+```Python hl_lines="8 9 10 11 12"
+{!../../../docs_src/settings/app02/main.py!}
+```
+
+And then we can require it from the *path operation function* as a dependency and use it anywhere we need it.
+
+```Python hl_lines="16  18 19 20"
+{!../../../docs_src/settings/app02/main.py!}
+```
+
+### Settings and testing
+
+Then it would be very easy to provide a different settings object during testing by creating a dependency override for `get_settings`:
+
+```Python hl_lines="8 9  12  21"
+{!../../../docs_src/settings/app02/test_main.py!}
+```
+
+In the dependency override we set a new value for the `admin_email` when creating the new `Settings` object, and then we return that new object.
+
+Then we can test that it is used.
+
+## Reading a `.env` file
+
+If you have many settings that possibly change a lot, maybe in different environments, it might be useful to put them on a file and then read them from it as if they were environment variables.
+
+This practice is common enough that it has a name, these environment variables are commonly placed in a file `.env`, and the file is called a "dotenv".
+
+!!! tip
+    A file starting with a dot (`.`) is a hidden file in Unix-like systems, like Linux and macOS.
+
+    But a dotenv file doesn't really have to have that exact filename.
+
+Pydantic has support for reading from these types of files using an external library. You can read more at <a href="https://pydantic-docs.helpmanual.io/usage/settings/#dotenv-env-support" class="external-link" target="_blank">Pydantic Settings: Dotenv (.env) support</a>.
+
+!!! tip
+    For this to work, you need to `pip install python-dotenv`.
+
+### The `.env` file
+
+You could have a `.env` file with:
+
+```bash
+ADMIN_EMAIL="[email protected]"
+APP_NAME="ChimichangApp"
+```
+
+### Read settings from `.env`
+
+And then update your `config.py` with:
+
+```Python hl_lines="9 10"
+{!../../../docs_src/settings/app03/config.py!}
+```
+
+Here we create a class `Config` inside of your Pydantic `Settings` class, and set the `env_file` to the filename with the dotenv file we want to use.
+
+!!! tip
+    The `Config` class is used just for Pydantic configuration. You can read more at <a href="https://pydantic-docs.helpmanual.io/usage/model_config/" class="external-link" target="_blank">Pydantic Model Config</a>
+
+### Creating the settings object
+
+Reading a file from disk is normally a costly (slow) operation, so you probably want to do it only once and then re-use the same settings, instead of reading it for each request.
+
+Because of that, in the dependency function, we first check if we already have a `settings` object, and create a new one (that could read from disk) only if it's still `None`, so, it would happen only the first time:
+
+```Python hl_lines="9 10 11 12"
+{!../../../docs_src/settings/app03/main.py!}
+```
+
+## Recap
+
+You can use Pydantic Settings to handle the settings or configurations for your application, with all the power of Pydantic models.
+
+* By using a dependency you can simplify testing.
+* You can use `.env` files with it.
+* Saving the settings in a variable lets you avoid reading the dotenv file again and again for each request.

docs/en/docs/tutorial/application-configuration.md → docs/en/docs/tutorial/metadata.md

@@ -1,25 +1,25 @@
-# Application Configuration
+# Metadata and Docs URLs
 
-There are several things that you can configure in your FastAPI application.
+You can customize several metadata configurations in your **FastAPI** application.
 
 ## Title, description, and version
 
 You can set the:
 
-* Title: used as your API's title/name, in OpenAPI and the automatic API docs UIs.
-* Description: the description of your API, in OpenAPI and the automatic API docs UIs.
-* Version: the version of your API, e.g. `v2` or `2.5.0`.
+* **Title**: used as your API's title/name, in OpenAPI and the automatic API docs UIs.
+* **Description**: the description of your API, in OpenAPI and the automatic API docs UIs.
+* **Version**: the version of your API, e.g. `v2` or `2.5.0`.
     * Useful for example if you had a previous version of the application, also using OpenAPI.
 
 To set them, use the parameters `title`, `description`, and `version`:
 
 ```Python hl_lines="4 5 6"
-{!../../../docs_src/application_configuration/tutorial001.py!}
+{!../../../docs_src/metadata/tutorial001.py!}
 ```
 
 With this configuration, the automatic API docs would look like:
 
-<img src="/img/tutorial/application-configuration/image01.png">
+<img src="/img/tutorial/metadata/image01.png">
 
 ## OpenAPI URL
 
@@ -30,7 +30,7 @@ But you can configure it with the parameter `openapi_url`.
 For example, to set it to be served at `/api/v1/openapi.json`:
 
 ```Python hl_lines="3"
-{!../../../docs_src/application_configuration/tutorial002.py!}
+{!../../../docs_src/metadata/tutorial002.py!}
 ```
 
 If you want to disable the OpenAPI schema completely you can set `openapi_url=None`.
@@ -49,5 +49,5 @@ You can configure the two documentation user interfaces included:
 For example, to set Swagger UI to be served at `/documentation` and disable ReDoc:
 
 ```Python hl_lines="3"
-{!../../../docs_src/application_configuration/tutorial003.py!}
+{!../../../docs_src/metadata/tutorial003.py!}
 ```

docs/en/mkdocs.yml

@@ -65,7 +65,7 @@ nav:
   - tutorial/sql-databases.md
   - tutorial/bigger-applications.md
   - tutorial/background-tasks.md
-  - tutorial/application-configuration.md
+  - tutorial/metadata.md
   - tutorial/static-files.md
   - tutorial/testing.md
   - tutorial/debugging.md
@@ -98,6 +98,7 @@ nav:
   - advanced/testing-websockets.md
   - advanced/testing-events.md
   - advanced/testing-dependencies.md
+  - advanced/settings.md
   - advanced/extending-openapi.md
   - advanced/openapi-callbacks.md
   - advanced/wsgi.md

docs_src/settings/app01/config.py

@@ -0,0 +1,10 @@
+from pydantic import BaseSettings
+
+
+class Settings(BaseSettings):
+    app_name: str = "Awesome API"
+    admin_email: str
+    items_per_user: int = 50
+
+
+settings = Settings()

docs_src/settings/app01/main.py

@@ -0,0 +1,14 @@
+from fastapi import FastAPI
+
+from . import config
+
+app = FastAPI()
+
+
+@app.get("/info")
+async def info():
+    return {
+        "app_name": config.settings.app_name,
+        "admin_email": config.settings.admin_email,
+        "items_per_user": config.settings.items_per_user,
+    }

docs_src/settings/app02/config.py

@@ -0,0 +1,10 @@
+from pydantic import BaseSettings
+
+
+class Settings(BaseSettings):
+    app_name: str = "Awesome API"
+    admin_email: str
+    items_per_user: int = 50
+
+
+settings: Settings = None

docs_src/settings/app02/main.py

@@ -0,0 +1,21 @@
+from fastapi import Depends, FastAPI
+
+from . import config
+
+app = FastAPI()
+
+
+def get_settings():
+    if config.settings:
+        return config.settings
+    config.settings = config.Settings()
+    return config.settings
+
+
+@app.get("/info")
+async def info(settings: config.Settings = Depends(get_settings)):
+    return {
+        "app_name": settings.app_name,
+        "admin_email": settings.admin_email,
+        "items_per_user": settings.items_per_user,
+    }

docs_src/settings/app02/test_main.py

@@ -0,0 +1,23 @@
+from fastapi.testclient import TestClient
+
+from . import config, main
+
+client = TestClient(main.app)
+
+
+def get_settings_override():
+    return config.Settings(admin_email="[email protected]")
+
+
+main.app.dependency_overrides[main.get_settings] = get_settings_override
+
+
+def test_app():
+
+    response = client.get("/info")
+    data = response.json()
+    assert data == {
+        "app_name": "Awesome API",
+        "admin_email": "[email protected]",
+        "items_per_user": 50,
+    }

docs_src/settings/app03/config.py

@@ -0,0 +1,13 @@
+from pydantic import BaseSettings
+
+
+class Settings(BaseSettings):
+    app_name: str = "Awesome API"
+    admin_email: str
+    items_per_user: int = 50
+
+    class Config:
+        env_file = ".env"
+
+
+settings: Settings = None

docs_src/settings/app03/main.py

@@ -0,0 +1,21 @@
+from fastapi import Depends, FastAPI
+
+from . import config
+
+app = FastAPI()
+
+
+def get_settings():
+    if config.settings:
+        return config.settings
+    config.settings = config.Settings()
+    return config.settings
+
+
+@app.get("/info")
+async def info(settings: config.Settings = Depends(get_settings)):
+    return {
+        "app_name": settings.app_name,
+        "admin_email": settings.admin_email,
+        "items_per_user": settings.items_per_user,
+    }

docs_src/settings/tutorial001.py

@@ -0,0 +1,21 @@
+from fastapi import FastAPI
+from pydantic import BaseSettings
+
+
+class Settings(BaseSettings):
+    app_name: str = "Awesome API"
+    admin_email: str
+    items_per_user: int = 50
+
+
+settings = Settings()
+app = FastAPI()
+
+
+@app.get("/info")
+async def info():
+    return {
+        "app_name": settings.app_name,
+        "admin_email": settings.admin_email,
+        "items_per_user": settings.items_per_user,
+    }

tests/test_tutorial/test_application_configuration/test_tutorial001.py → tests/test_tutorial/test_metadata/test_tutorial001.py

@@ -1,6 +1,6 @@
 from fastapi.testclient import TestClient
 
-from application_configuration.tutorial001 import app
+from metadata.tutorial001 import app
 
 client = TestClient(app)
 

tests/test_tutorial/test_settings/test_app02.py

@@ -0,0 +1,9 @@
+from fastapi.testclient import TestClient
+
+from settings.app02 import main, test_main
+
+client = TestClient(main.app)
+
+
+def test_setting_override():
+    test_main.test_app()