*
     * <ul>
     *   <li>For an empty list, it is 1 (base case).
     *   <li>When r numbers are added to a list of n-r elements, the number of permutations is
     *       increased by a factor of (n choose r).
     * </ul>
     */
    private static <E> int calculateSize(
        List<E> sortedInputList, Comparator<? super E> comparator) {
      int permutations = 1;
      int n = 1;
      int r = 1;

---

Se você simplesmente não sabe, use apenas `def`.

---

**Note**: Você pode misturar `def` e `async def` nas suas *funções de operação de rota* tanto quanto necessário e definir cada função usando a melhor opção para você. FastAPI irá fazer a coisa certa com elas.

De qualquer forma, em ambos os casos acima, FastAPI irá trabalhar assincronamente e ser extremamente rápido.

## What makes a dependency

Up to now you have seen dependencies declared as functions.

But that's not the only way to declare dependencies (although it would probably be the more common).

The key factor is that a dependency should be a "callable".

A "**callable**" in Python is anything that Python can "call" like a function.

absl-py==2.1.0 \
    --hash=sha256:526a04eadab8b4ee719ce68f204172ead1027549089702d99b9059f129ff1308 \
    --hash=sha256:7820790efbb316739cde8b4e19357243fc3608a152024288513dd968d7d959ff
    # via
    #   keras-nightly
    #   tb-nightly
astor==0.7.1 \
    --hash=sha256:95c30d87a6c2cf89aa628b87398466840f0ad8652f88eb173125a6df8533fb8d \
    --hash=sha256:fb503b9e2fdd05609fbf557b916b4a7824171203701660f0c55bbf5a7a68713e
    # via -r requirements.in
astunparse==1.6.3 \

absl-py==2.1.0 \
    --hash=sha256:526a04eadab8b4ee719ce68f204172ead1027549089702d99b9059f129ff1308 \
    --hash=sha256:7820790efbb316739cde8b4e19357243fc3608a152024288513dd968d7d959ff
    # via
    #   keras-nightly
    #   tb-nightly
astor==0.7.1 \
    --hash=sha256:95c30d87a6c2cf89aa628b87398466840f0ad8652f88eb173125a6df8533fb8d \
    --hash=sha256:fb503b9e2fdd05609fbf557b916b4a7824171203701660f0c55bbf5a7a68713e
    # via -r requirements.in
astunparse==1.6.3 \

[
  {
    "name": "antlr",
    "path": "platforms/software/antlr",
    "unitTests": true,
    "functionalTests": true,
    "crossVersionTests": false
  },
  {
    "name": "api-metadata",
    "path": "platforms/core-configuration/api-metadata",
    "unitTests": false,
    "functionalTests": false,
    "crossVersionTests": false
  },
  {
    "name": "architecture-test",
    "path": "testing/architecture-test",

     *
     * <ul>
     *   <li>For an empty list, it is 1 (base case).
     *   <li>When r numbers are added to a list of n-r elements, the number of permutations is
     *       increased by a factor of (n choose r).
     * </ul>
     */
    private static <E> int calculateSize(
        List<E> sortedInputList, Comparator<? super E> comparator) {
      int permutations = 1;
      int n = 1;
      int r = 1;

$ 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

- cloud.google.com/go/workflows: v1.10.0
- github.com/alecthomas/kingpin/v2: [v2.3.2](https://github.com/alecthomas/kingpin/v2/tree/v2.3.2)
- github.com/antlr/antlr4/runtime/Go/antlr/v4: [8188dc5](https://github.com/antlr/antlr4/runtime/Go/antlr/v4/tree/8188dc5)
- github.com/google/gnostic-models: [v0.6.8](https://github.com/google/gnostic-models/tree/v0.6.8)

// 之后环境变量不再存在
$ python main.py

Hello World from Python
```

</div>

!!! tip
    您可以在 <a href="https://12factor.net/config" class="external-link" target="_blank">Twelve-Factor App: Config</a> 中阅读更多相关信息。

### 类型和验证

这些环境变量只能处理文本字符串，因为它们是外部于 Python 的，并且必须与其他程序和整个系统兼容（甚至与不同的操作系统，如 Linux、Windows、macOS）。

这意味着从环境变量中在 Python 中读取的任何值都将是 `str` 类型，任何类型的转换或验证都必须在代码中完成。