Birden fazla kasiyer varken (varsayalım 8) sıraya girdiniz👩‍🍳👨‍🍳👩‍🍳👨‍🍳👩‍🍳👨‍🍳👩‍🍳👨‍🍳 ve sıranız gelene kadar bekliyorsunuz.

Sizden önceki herkez ayrılmadan önce hamburgerlerinin 🍔 hazır olmasını bekliyor 🕙. Çünkü kasiyerlerin her biri bir hamburger hazırlanmadan önce bir sonraki siparişe geçmiiyor.

Sonunda senin sıran, aşkın 😍 ve kendin için 2 hamburger 🍔 siparişi verdiniz.

Ödemeyi yaptınız 💸.

	}

	e = Erasure{
		dataBlocks:   dataBlocks,
		parityBlocks: parityBlocks,
		blockSize:    blockSize,
	}

	// Encoder when needed.
	var enc reedsolomon.Encoder
	var once sync.Once
	e.encoder = func() reedsolomon.Encoder {
		once.Do(func() {
			e, err := reedsolomon.New(dataBlocks, parityBlocks, reedsolomon.WithAutoGoroutines(int(e.ShardSize())))
			if err != nil {
				// Error conditions should be checked above.

But here's the key point.

The security and dependency injection stuff is written once.

And you can make it as complex as you want. And still, have it written only once, in a single place. With all the flexibility.

But you can have thousands of endpoints (*path operations*) using the same security system.

### Creating the `Settings` only once with `lru_cache` { #creating-the-settings-only-once-with-lru-cache }

Reading a file from disk is normally a costly (slow) operation, so you probably want to do it only once and then reuse the same settings object, instead of reading it for each request.

But every time we do:

```Python
Settings()

# ==============================================================================

load("@python//:defs.bzl", "compile_pip_requirements")
load("@python_version_repo//:py_version.bzl", "REQUIREMENTS")

# TODO(ybaturina): Remove once TF is migrated to CUDA 12.9.
genrule(
    name = "nvidia_constraints",
    srcs = ["nvidia-requirements.txt"],
    outs = ["nvidia-constraints.txt"],
    cmd = """sed -E "s/>=/==/" $(location nvidia-requirements.txt) > $@;""",

This provider might be charging you per request, and calling it might take some extra time than if you had a fixed mock user for tests.

You probably want to test the external provider once, but not necessarily call it for every test that runs.

In this case, you can override the dependency that calls that provider, and use a custom dependency that returns a mock user, only for your tests.

You can define logic (code) that should be executed before the application **starts up**. This means that this code will be executed **once**, **before** the application **starts receiving requests**.

The same way, you can define logic (code) that should be executed when the application is **shutting down**. In this case, this code will be executed **once**, **after** having handled possibly **many requests**.

	if len(args.Resources) > maxDeleteList {
		return false, fmt.Errorf("internal error: localLocker.Lock called with more than %d resources", maxDeleteList)
	}

	// If we have too many waiting, reject this at once.
	if l.waitMutex.Load() > lockMutexWaitLimit {
		l.locksOverloaded.Add(1)
		return false, nil
	}
	// Wait for mutex
	defer l.getMutex()()
	if ctx.Err() != nil {
		return false, ctx.Err()
	}

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

## Query Parameters with a Pydantic Model { #query-parameters-with-a-pydantic-model }

/// tip

You normally have to do this only **once**, when you create the virtual environment.

///

## Deactivate the Virtual Environment { #deactivate-the-virtual-environment }

Once you are done working on your project you can **deactivate** the virtual environment.

<div class="termy">

```console
$ deactivate
```