print(f"Hello {name} from Python")
```

/// tip

第二个参数是 <a href="https://docs.python.org/zh-cn/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> 的默认返回值。

如果没有提供，默认值为 `None`，这里我们提供 `"World"` 作为默认值。

///

然后你可以调用这个 Python 程序：

//// tab | Linux, macOS, Windows Bash

<div class="termy">

```console
// 这里我们还没有设置环境变量
$ python main.py

// 因为我们没有设置环境变量，所以我们得到的是默认值

	}
	var count int
	var errRepeat = errors.New("repeated call to path")
	err = fs.WalkDir(zr, ".", func(p string, d fs.DirEntry, err error) error {
		count++
		if count > 2 { // once for directory read, once for the error
			return errRepeat
		}
		return err
	})
	if err == nil {
		t.Fatalf("expected error from invalid file name")
	} else if errors.Is(err, errRepeat) {
		t.Fatal(err)
	}

graph TB

common_parameters(["common_parameters"])
read_items["/items/"]
read_users["/users/"]

common_parameters --> read_items
common_parameters --> read_users
```

This way you write shared code once and **FastAPI** takes care of calling it for your *path operations*.

/// check

Notice that you don't have to create a special class and pass it somewhere to **FastAPI** to "register" it or anything similar.

* Data "<abbr title="converting the string that comes from an HTTP request into Python data">parsing</abbr>"
* Data validation
* API annotation and automatic documentation

And you only have to declare them once.

      auto& indices = iter->second;
      if (std::find(indices.begin(), indices.end(), idx) != indices.end()) {
        return InvalidArgument("TF_Output ", node->name(), ":", idx,
                               " appears more than once in the input list");
      }
      indices.push_back(idx);
    }
  }
  return absl::OkStatus();
}

// Converts `noutputs` and `outputs` into `outputs_tensors` and does various
// checks while doing so.

	newSignature := getSignature(signingKey, stringToSign)

	// Verify if signature match.
	if !compareSignatureV4(newSignature, signV4Values.Signature) {
		return ErrSignatureDoesNotMatch
	}

	// Return error none.
	return ErrNone

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

### Dockerfile { #dockerfile }

Теперь в той же директории проекта создайте файл `Dockerfile`:

```{ .dockerfile .annotate }
# (1)!

### Creando el `Settings` solo una vez con `lru_cache` { #creating-the-settings-only-once-with-lru-cache }

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

### Dockerfile { #dockerfile }

Erstellen Sie nun im selben Projektverzeichnis eine Datei `Dockerfile` mit:

```{ .dockerfile .annotate }
# (1)!

				CheckUser(t, models3[idx], user)
			})
		}
	}

	var none []User
	if err := DB.Where("name in (?)", []string{}).Find(&none).Error; err != nil || len(none) != 0 {
		t.Errorf("errors happened when query find with in clause and zero length parameter: %v, length: %v", err, len(none))
	}
}

func TestQueryWithAssociation(t *testing.T) {