Actually, all (or most) of the web frameworks work in this same way.

You never call those functions directly. They are called by your framework (in this case, **FastAPI**).

With the Dependency Injection system, you can also tell **FastAPI** that your *path operation function* also "depends" on something else that should be executed before your *path operation function*, and **FastAPI** will take care of executing it and "injecting" the results.

## In a hurry? { #in-a-hurry }

<abbr title="too long; didn't read"><strong>TL;DR:</strong></abbr>

If you are using third party libraries that tell you to call them with `await`, like:

```Python
results = await some_library()
```

Then, declare your *path operation functions* with `async def` like:

```Python hl_lines="2"
@app.get('/')

      val pkcs8Bytes =
        pkcs8Base64Text.decodeBase64()
          ?: throw IllegalArgumentException("failed to decode private key")

      // The private key doesn't tell us its type but it's okay because the certificate knows!
      val keyType =
        when (certificate.publicKey) {
          is ECPublicKey -> "EC"
          is RSAPublicKey -> "RSA"

   * correctly requests of varying weight (permits), /no matter/ what the actual function is - so we
   * can tweak the latter freely. (The only requirement, obviously, is that we can compute its
   * integrals).
   *
   * Note well that if, for this function, we chose a horizontal line, at height of exactly (1/QPS),
   * then the effect of the function is non-existent: we serve storedPermits at exactly the same

/// tip

If you have strict type checks in your editor, mypy, etc, you can declare the function return type as `Any`.

That way you tell the editor that you are intentionally returning anything. But FastAPI will still do the data documentation, validation, filtering, etc. with the `response_model`.

///

### `response_model` Priority { #response-model-priority }

            //
            // 2. not to cancel any Future the user returned from an AsyncCallable
            //
            // We promise this because, once we cancel that Future, we would no longer be able to
            // tell when any underlying work it is doing is done. Thus, we might start a new task
            // while that underlying work is still running.
            //
            // So that is why we cancel only in the case of CAS success.

   * or resource constraints) accept without blocking. This is always equal to the initial capacity
   * of this queue less the current {@code size} of this queue.
   *
   * <p>Note that you cannot always tell if an attempt to insert an element will succeed by
   * inspecting {@code remainingCapacity} because it may be the case that another thread is about to
   * insert or remove an element.
   */
  @CanIgnoreReturnValue

* <a href="https://x.com/tiangolo" class="external-link" target="_blank">Follow me on **X (Twitter)**</a> or <a href="https://fosstodon.org/@tiangolo" class="external-link" target="_blank">Mastodon</a>.
    * Tell me how you use FastAPI (I love to hear that).
    * Hear when I make announcements or release new tools.

	if err := applyDynamicConfigForSubSys(GlobalContext, objectAPI, cfg, subSys); err != nil {
		writeErrorResponseJSON(ctx, w, toAdminAPIErr(ctx, err), r.URL)
		return
	}
	globalNotificationSys.SignalConfigReload(subSys)
	// Tell the client that dynamic config was applied.
	w.Header().Set(madmin.ConfigAppliedHeader, madmin.ConfigAppliedTrue)
}

type badConfigErr struct {
	Err error
}

// Error - return the error message

But if you know that you won't need to use the dependency after returning from the *path operation function*, you can use `Depends(scope="function")` to tell FastAPI that it should close the dependency after the *path operation function* returns, but **before** the **response is sent**.

{* ../../docs_src/dependencies/tutorial008e_an_py39.py hl[12,16] *}