if b.lastRead <= opInvalid {
		return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune")
	}
	if b.off >= int(b.lastRead) {
		b.off -= int(b.lastRead)
	}
	b.lastRead = opInvalid
	return nil
}

var errUnreadByte = errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read")

# Simple OAuth2 with Password and Bearer { #simple-oauth2-with-password-and-bearer }

Now let's build from the previous chapter and add the missing parts to have a complete security flow.

## Get the `username` and `password` { #get-the-username-and-password }

We are going to use **FastAPI** security utilities to get the `username` and `password`.

And it was thoroughly tested at the design phase, before any implementation, to ensure it would work with all the editors.

There were even some changes to Pydantic itself to support this.

The previous screenshots were taken with [Visual Studio Code](https://code.visualstudio.com).

But you would get the same editor support with [PyCharm](https://www.jetbrains.com/pycharm/) and most of the other Python editors:

                    session.setAttribute(Constants.RESULTS_PER_PAGE, form.num);
                }
            });
        }
        return doSearch(form);
    }

    /**
     * The previous page.
     * @param form The search form.
     * @return The HTML response.
     */
    @Execute
    public HtmlResponse prev(final SearchForm form) {
        return doMove(form, -1);
    }

    /**

	dst   chan [][]string // result of block decode
	err   error           // any error encountered will be set here
}

// Read - reads single record.
// Once Read is called the previous record should no longer be referenced.
func (r *Reader) Read(dst sql.Record) (sql.Record, error) {
	// If we have have any records left, return these before any error.
	for len(r.current) <= r.recordsRead {
		if r.err != nil {

# 以類別作為相依性 { #classes-as-dependencies }

在更深入了解 **相依性注入（Dependency Injection）** 系統之前，我們先把前一個範例升級一下。

## 前一個範例中的 `dict` { #a-dict-from-the-previous-example }

在前一個範例中，我們從相依項（"dependable"）回傳了一個 `dict`：

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[9] *}

但接著我們在路徑操作函式（*path operation function*）的參數 `commons` 中取得的是一個 `dict`。

而我們知道，編輯器對 `dict` 無法提供太多輔助（例如自動完成），因為它無法預先知道其中的鍵與值的型別。

我們可以做得更好...

    // correct.
    this.state.markReady();
  }

  /**
   * Registers a {@link Listener} to be {@linkplain Executor#execute executed} on the given
   * executor. The listener will not have previous state changes replayed, so it is suggested that
   * listeners are added before any of the managed services are {@linkplain Service#startAsync
   * started}.
   *

/// tip

先別擔心這裡提到的「容器」、Docker 或 Kubernetes 如果現在還不太懂。

我會在未來的章節進一步說明容器映像、Docker、Kubernetes 等等：[容器中的 FastAPI - Docker](docker.md)。

///

## 啟動前的前置步驟 { #previous-steps-before-starting }

很多情況下，你會希望在應用「啟動之前」先執行一些步驟。

例如，你可能想先執行「資料庫遷移」。

但在多數情況下，你會希望這些步驟只執行「一次」。

所以，你會希望用「單一行程」來執行那些「前置步驟」，在啟動應用之前完成。

 * {@code Comparator} doesn't: it evaluates all the parameters of all the {@code .compare} calls,
 * even when the result of the comparison is already known from previous {@code .compare} calls.
 * That can be expensive.
 *
 * @author Mark Davis
 * @author Kevin Bourrillion
 * @since 2.0
 */
@GwtCompatible
public abstract class ComparisonChain {
  private ComparisonChain() {}

	}

	if cap(t.requestsPool) != apiRequestsMaxPerNode {
		// Only replace if needed.
		// Existing requests will use the previous limit,
		// but new requests will use the new limit.
		// There will be a short overlap window,
		// but this shouldn't last long.
		t.requestsPool = make(chan struct{}, apiRequestsMaxPerNode)
	}