## 情境管理器 { #context-managers }

### 什麼是「情境管理器」 { #what-are-context-managers }

「情境管理器」是那些你可以在 `with` 陳述式中使用的 Python 物件。

例如，[你可以用 `with` 來讀取檔案](https://docs.python.org/3/tutorial/inputoutput.html#reading-and-writing-files)：

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

在底層，`open("./somefile.txt")` 會建立一個稱為「情境管理器」的物件。

            int hash = (auth.getUsername() + auth.getPassword()).hashCode();
            buffer.append(hash).append('@');
        }

        // consider the URL (instead of the id) as this most closely relates to the contents in the repo
        buffer.append(repository.getUrl());

        return buffer.toString();
    }

    private void writeLastUpdated(File touchfile, String key, String error) {

   * objects, and the array itself, can be null. That is for programmer convenience, when the
   * objects come from factory methods that are themselves {@code @Nullable}. In reality neither the
   * array nor its contents can be null, but it is not useful to force the use of {@code
   * requireNonNull} or the like just to assert that.
   *
   * <p>{@code EqualsTester} will always check that every object it is given returns false from

import java.io.Serializable;
import java.util.Map;
import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;

/**
 * A {@link ClassToInstanceMap} whose contents will never change, with many other important
 * properties detailed at {@link ImmutableCollection}.
 *
 * @author Kevin Bourrillion
 * @since 2.0
 */
@Immutable(containerOf = "B")
@GwtIncompatible

    if (entries.size() >= 1) {
      a = entries.get(0);
      if (entries.size() >= 3) {
        b = entries.get(1);
        c = entries.get(2);
      }
    }
  }

  /** Resets the contents of navigableMap to have entries a, c, for the navigation tests. */
  @SuppressWarnings("unchecked") // Needed to stop Eclipse whining
  private void resetWithHole() {

    if (entries.size() >= 1) {
      a = entries.get(0);
      if (entries.size() >= 3) {
        b = entries.get(1);
        c = entries.get(2);
      }
    }
  }

  /** Resets the contents of navigableMap to have entries a, c, for the navigation tests. */
  @SuppressWarnings("unchecked") // Needed to stop Eclipse whining
  private void resetWithHole() {

  }

  /**
   * This decodes a value into its contents using a preceding member of the same SEQUENCE. For
   * example, extensions type IDs specify what types to use for the corresponding values.
   *
   * If the hint is unknown [chooser] should return null which will cause the value to be decoded as
   * an opaque byte string.
   *
   * This may optionally wrap the contents in a tag.
   */

    public Builder<N> putEdge(EndpointPair<N> endpoints) {
      mutableGraph.putEdge(endpoints);
      return this;
    }

    /**
     * Returns a newly-created {@code ImmutableGraph} based on the contents of this {@code Builder}.
     */
    public ImmutableGraph<N> build() {
      return ImmutableGraph.copyOf(mutableGraph);
    }
  }

        try {
            return new JarFile(file);
        } catch (final IOException e) {
            throw new IORuntimeException(e);
        }
    }

    /**
     * Returns an input stream to read the contents of the specified JAR file entry.
     *
     * @param file the JAR file (must not be {@literal null})
     * @param entry the JAR file entry (must not be {@literal null})
     * @return the input stream to read the entry

        for (Element element : keys) {
          builder.put(element, element);
        }
        return builder.build();
      }
    };

    abstract Map<Element, Element> create(Collection<Element> contents);
  }

  @Param({"5", "50", "500", "5000", "50000"})
  private int size;

  // TODO: look at exact (==) hits vs. equals() hits?
  @Param("0.9")
  private double hitRate;

  @Param("true")