* So, by using FastAPI you are saving development time, bugs, lines of code, and you would probably get the same performance (or better) you would if you didn't use it (as you would have to implement it all in your code).

{* ../../docs_src/path_operation_configuration/tutorial003_py310.py hl[18:19] *}

## Description from docstring { #description-from-docstring }

## Documenting the callback { #documenting-the-callback }

The actual callback code will depend heavily on your own API app.

And it will probably vary a lot from one app to the next.

It could be just one or two lines of code, like:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

$ export MY_NAME="Wade Wilson"

// Then you could use it with other programs, like
$ echo "Hello $MY_NAME"

Hello Wade Wilson
```

</div>

////

//// tab | Windows PowerShell

<div class="termy">

```console
// Create an env var MY_NAME
$ $Env:MY_NAME = "Wade Wilson"

// Use it with other programs, like
$ echo "Hello $Env:MY_NAME"

Hello Wade Wilson
```

</div>

////

          // it is kind of lame that we need to construct a decoder to access this value.
          // if this is a concern we could add special cases for some known charsets (like utf8)
          // or we could avoid inputstreamreader and use the decoder api directly
          // TODO(lukes): in a real implementation we would need to handle overflow conditions
          int maxChars = (int) (size.get().intValue() * cs.newDecoder().maxCharsPerByte());

<img src="/img/tutorial/security/image03.png">

We are not verifying the validity of the token yet, but that's a start already.

## Recap { #recap }

   *
   *   o DIRTY lines track that an entry is actively being created or updated. Every successful
   *     DIRTY action should be followed by a CLEAN or REMOVE action. DIRTY lines without a matching
   *     CLEAN or REMOVE indicate that temporary files may need to be deleted.
   *
   *   o CLEAN lines track a cache entry that has been successfully published and may be read. A

     * TLSv1.2
     * ```
     *
     * The file is newline separated. The first two lines are the URL and the request method. Next
     * is the number of HTTP Vary request header lines, followed by those lines.
     *
     * Next is the response status line, followed by the number of HTTP response header lines,
     * followed by those lines.
     *

It is just a function that can take all the same parameters that a *path operation function* can take:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

That's it.

**2 lines**.

And it has the same shape and structure that all your *path operation functions* have.

You can think of it as a *path operation function* without the "decorator" (without the `@app.get("/some-path")`).

 * JavaScript parser `urltestparser.js` with which this class attempts to be compatible.
 *
 * Each line of the `urltestdata.txt` file specifies a test. Lines look like this:
 *
 * ```
 * http://example\t.\norg http://example.org/foo/bar s:http h:example.org p:/
 * ```
 */
class WebPlatformUrlTestData {
  var input: String? = null
  var base: String? = null