```Python hl_lines="1  4"
    {!> ../../../docs_src/python_types/tutorial008b.py!}
    ```

In both cases this means that `item` could be an `int` or a `str`.

#### Possibly `None`

You can declare that a value could have a type, like `str`, but that it could also be `None`.

In Python 3.6 and above (including Python 3.10) you can declare it by importing and using `Optional` from the `typing` module.

                    visitTree(classDetails, classesDir, jarOutputStream, visited)
                }
            }
        } catch (exception: Exception) {
            throw ClassAnalysisException("Could not write shaded Jar $jarFile", exception)
        }
    }

    private
    fun visitTree(
        classDetails: ClassDetails,
        classesDir: File,
        jarOutputStream: JarOutputStream,

# Read the "|" not as "or", but as a "pipe", taking the output of the previous command and passing it to the next command.
# This section could also appear ahead of the automations section.

colors:

!!! note "Technical Details"
    You could also use `from starlette.requests import Request`.

    **FastAPI** provides it as a convenience for you, the developer. But it comes directly from Starlette.

### Before and after the `response`

So, the URL for that file would be something like: `/files/home/johndoe/myfile.txt`.

### OpenAPI support

OpenAPI doesn't support a way to declare a *path parameter* to contain a *path* inside, as that could lead to scenarios that are difficult to test and define.

Nevertheless, you can still do it in **FastAPI**, using one of the internal tools from Starlette.

    `OAuth2PasswordBearer` makes **FastAPI** know that it is a security scheme. So it is added that way to OpenAPI.

    But `OAuth2PasswordRequestForm` is just a class dependency that you could have written yourself, or you could have declared `Form` parameters directly.

    But as it's a common use case, it is provided by **FastAPI** directly, just to make it easier.

### Use the form data

!!! tip

                            writeBytes(classWriter.toByteArray())
                        }
                    } catch (exception: Exception) {
                        throw ClassAnalysisException("Could not transform class from ${file.toFile()}", exception)
                    }
                }
            }
        )
    }
}


fun JarOutputStream.addJarEntry(entryName: String, sourceFile: File) {

## Compiler {#compiler}

The build time overhead to building with [Profile Guided Optimization](/doc/pgo) has been reduced significantly.
Previously, large builds could see 100%+ build time increase from enabling PGO.
In Go 1.23, overhead should be in the single digit percentages.

## Assembler {#assembler}

#### What is OpenAPI for

The OpenAPI schema is what powers the two interactive documentation systems included.

And there are dozens of alternatives, all based on OpenAPI. You could easily add any of those alternatives to your application built with **FastAPI**.

You could also use it to generate code automatically, for clients that communicate with your API. For example, frontend, mobile or IoT applications.

## Recap, step by step

    It might also help avoid confusion for new developers that see an unused parameter in your code and could think it's unnecessary.

!!! info
    In this example we use invented custom headers `X-Key` and `X-Token`.

    But in real cases, when implementing security, you would get more benefits from using the integrated [Security utilities (the next chapter)](../security/index.md){.internal-link target=_blank}.