// Every node is, at a minimum, reachable from itself. Since the resulting transitive closure
    // will have no isolated nodes, we can skip adding nodes explicitly and let putEdge() do it.

    if (graph.isDirected()) {
      // Note: works for both directed and undirected graphs, but we only use in the directed case.
      for (N node : graph.nodes()) {

          </description>
        </field>
        <field>
          <name>expression</name>
          <version>2.0.0+</version>
          <type>String</type>
          <description>Parameter expression, to let user override default value with a user property, system property or project property.</description>
        </field>
        <field>
          <name>defaultValue</name>
          <version>2.0.0+</version>

```Python hl_lines="1  4"
{!../../docs_src/python_types/tutorial009.py!}
```

Using `Optional[str]` instead of just `str` will let the editor help you detect errors where you could be assuming that a value is always a `str`, when it could actually be `None` too.

`Optional[Something]` is actually a shortcut for `Union[Something, None]`, they are equivalent.

## Proxy Forwarded Headers { #proxy-forwarded-headers }

A **proxy** in front of your application would normally set some headers on the fly before sending the requests to your **server** to let the server know that the request was **forwarded** by the proxy, letting it know the original (public) URL, including the domain, that it is using HTTPS, etc.

  @GwtIncompatible // regular expressions
  private static
  java.util.regex.Pattern
      fpPattern() {
    /*
     * We use # instead of * for possessive quantifiers. This lets us strip them out when building
     * the regex for RE2 (which doesn't support them) but leave them in when building it for
     * java.util.regex (where we want them in order to avoid catastrophic backtracking).
     */

 *
 * ```java
 * HttpUrl url = HttpUrl.parse("http://who-let-the-dogs.out").newBuilder()
 *     .addPathSegment("_Who?_")
 *     .query("_Who?_")
 *     .fragment("_Who?_")
 *     .build();
 * System.out.println(url);
 * ```
 *
 * This prints:
 *
 * ```
 * http://who-let-the-dogs.out/_Who%3F_?_Who?_#_Who?_
 * ```
 *

Por outro lado, se você tem 2 servidores e está usando **100% da CPU e RAM deles**, em algum momento um processo pedirá mais memória, e o servidor terá que usar o disco como "memória" (o que pode ser milhares de vezes mais lento), ou até mesmo **travar**. Ou um processo pode precisar fazer alguma computação e teria que esperar até que a CPU esteja livre novamente.

* **Cloud services** that handle this for you
    * The cloud service will probably **handle replication for you**. It would possibly let you define **a process to run**, or a **container image** to use, in any case, it would most probably be **a single Uvicorn process**, and the cloud service would be in charge of replicating it.

/// tip

        | (b4 & 0xFFL) << 32
        | (b5 & 0xFFL) << 24
        | (b6 & 0xFFL) << 16
        | (b7 & 0xFFL) << 8
        | (b8 & 0xFFL);
  }

  /*
   * Moving asciiDigits into this static holder class lets ProGuard eliminate and inline the Longs
   * class.
   */
  static final class AsciiDigits {
    private AsciiDigits() {}

    private static final byte[] asciiDigits;

    static {

```

#### Docker Cache { #docker-cache }

There's an important trick in this `Dockerfile`, we first copy the **file with the dependencies alone**, not the rest of the code. Let me tell you why is that.

```Dockerfile
COPY ./requirements.txt /code/requirements.txt
```