///

## 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 any validation has to be done in code.

---

## **Typer**, giao diện dòng lệnh của FastAPI

<a href="https://typer.tiangolo.com" target="_blank"><img src="https://typer.tiangolo.com/img/logo-margin/logo-margin-vector.svg" style="width: 20%;"></a>

---

## **Typer**，命令行中的 FastAPI

<a href="https://typer.tiangolo.com" target="_blank"><img src="https://typer.tiangolo.com/img/logo-margin/logo-margin-vector.svg" style="width: 20%;"></a>

如果你正在开发一个在终端中运行的<abbr title="Command Line Interface">命令行</abbr>应用而不是 web API，不妨试下 <a href="https://typer.tiangolo.com/" class="external-link" target="_blank">**Typer**</a>。

**Typer** 是 FastAPI 的小同胞。它想要成为**命令行中的 FastAPI**。 ⌨️ 🚀

# Global Dependencies

For some types of applications you might want to add dependencies to the whole application.

Similar to the way you can [add `dependencies` to the *path operation decorators*](dependencies-in-path-operation-decorators.md){.internal-link target=_blank}, you can add them to the `FastAPI` application.

In that case, they will be applied to all the *path operations* in the application:

//// tab | Python 3.9+

```Python hl_lines="16"

  private static void assertFreshInstances(Class<?>... types) {
    for (Class<?> type : types) {
      assertFreshInstance(type, 2);
    }
  }

  private static void assertFreshInstance(TypeToken<?> type) {
    assertFreshInstance(type, 3);
  }

  private static void assertFreshInstance(Class<?> type, int instances) {
    assertFreshInstance(TypeToken.of(type), instances);
  }

interface rpc
{
	/* base types */

	typedef unsigned char uint8_t;
	typedef unsigned short uint16_t;
	typedef unsigned int uint32_t;

	/* dce */

	typedef struct {
	    uint32_t time_low;
	    uint16_t time_mid;
	    uint16_t time_hi_and_version;
	    uint8_t clock_seq_hi_and_reserved;
	    uint8_t clock_seq_low;
	    uint8_t node[6];
	} uuid_t;

	/* win32 stuff */

	typedef struct {
		uint32_t type;
		uuid_t uuid;

interface rpc
{
	/* base types */

	typedef unsigned char uint8_t;
	typedef unsigned short uint16_t;
	typedef unsigned int uint32_t;

	/* dce */

	typedef struct {
	    uint32_t time_low;
	    uint16_t time_mid;
	    uint16_t time_hi_and_version;
	    uint8_t clock_seq_hi_and_reserved;
	    uint8_t clock_seq_low;
	    uint8_t node[6];
	} uuid_t;

	/* win32 stuff */

	typedef struct {
		uint32_t type;
		uuid_t uuid;

For example, you cannot put a Pydantic model in a `JSONResponse` without first converting it to a `dict` with all the data types (like `datetime`, `UUID`, etc) converted to JSON-compatible types.

For those cases, you can use the `jsonable_encoder` to convert your data before passing it to a response:

```Python hl_lines="6-7  21-22"
{!../../docs_src/response_directly/tutorial001.py!}
```

        ForkFailed,
        ForkedProjectStarted,
        ForkedProjectSucceeded,
        ForkedProjectFailed,
    }

    /**
     * Gets the type of the event.
     *
     * @return The type of the event, never {@code null}.
     */
    Type getType();

    /**
     * Gets the session from which this event originates.
     *
     * @return The current session, never {@code null}.
     */

Some of the tasks they can perform include:

* Adding labels to PRs.
* Editing PR titles.
* Adding commits on top of PRs to tweak them.
* Mark answers in GitHub Discussions questions, etc.
* Merge some specific types of PRs.

You can see the current team members in [FastAPI People - Team](./fastapi-people.md#team){.internal-link target=_blank}.