## OpenAPI { #openapi }

OpenAPI (previously known as Swagger) is the open specification for building APIs (now part of the Linux Foundation).

**FastAPI** is based on **OpenAPI**.

That's what makes it possible to have multiple automatic interactive documentation interfaces, code generation, etc.

OpenAPI has a way to define multiple security "schemes".

        assertTrue(h.isValid());

        // Tree id change makes it invalid
        when(tree.getTreeId()).thenReturn(11L);
        assertFalse(h.isValid());

        // Connected=false makes it invalid
        when(tree.getTreeId()).thenReturn(10L);
        when(tree.isConnected()).thenReturn(false);
        assertFalse(h.isValid());

        // Mark closed makes it invalid
        when(tree.isConnected()).thenReturn(true);

		{Name: "file.go", Data: []byte("hello"), Mode: 0644},
		{Name: "subfolder/another.go", Data: []byte("world"), Mode: 0644},
		// Notably missing here is the "subfolder" directory. This makes sure even
		// if we don't have a subfolder directory listed.
	}
	err := w.AddFS(writeTestsToFS(tests))
	if err != nil {
		t.Fatal(err)
	}
	if err := w.Close(); err != nil {
		t.Fatal(err)
	}

In the same way, you can use `finally` to make sure the exit steps are executed, no matter if there was an exception or not.

{* ../../docs_src/dependencies/tutorial007_py39.py hl[3,5] *}

## Sub-dependencies with `yield` { #sub-dependencies-with-yield }

You can have sub-dependencies and "trees" of sub-dependencies of any size and shape, and any or all of them can use `yield`.

  sufficient copyright rights in its Contribution, if any, to grant
  the copyright license set forth in this Agreement.

  e) Notwithstanding the terms of any Secondary License, no
  Contributor makes additional grants to any Recipient (other than
  those set forth in this Agreement) as a result of such Recipient's
  receipt of the Program under the terms of a Secondary License
  (if permitted under the terms of Section 3).

	return err
}

// NewTierConfigMgr - creates new tier configuration manager,
func NewTierConfigMgr() *TierConfigMgr {
	return &TierConfigMgr{
		drivercache: make(map[string]WarmBackend),
		Tiers:       make(map[string]madmin.TierConfig),
	}
}

func (config *TierConfigMgr) refreshTierConfig(ctx context.Context, objAPI ObjectLayer) {
	const tierCfgRefresh = 15 * time.Minute

    * Tell me how you use FastAPI (I love to hear that).
    * Hear when I make announcements or release new tools.
    * You can also <a href="https://x.com/fastapi" class="external-link" target="_blank">follow @fastapi on X (Twitter)</a> (a separate account).
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You will see examples of this in the next chapters, about relational and NoSQL databases, security, etc.

## **FastAPI** compatibility { #fastapi-compatibility }

The simplicity of the dependency injection system makes **FastAPI** compatible with:

* all the relational databases
* NoSQL databases
* external packages
* external APIs
* authentication and authorization systems
* API usage monitoring systems

> Modern versions of Python have support for **"asynchronous code"** using something called **"coroutines"**, with **`async` and `await`** syntax.

That should make more sense now. ✨

All that is what powers FastAPI (through Starlette) and what makes it have such an impressive performance.

## Very Technical Details { #very-technical-details }

/// warning

You can probably skip this.

/// note

Having a default value of any type, including `None`, makes the parameter optional (not required).

///

## Required parameters { #required-parameters }

When we don't need to declare more validations or metadata, we can make the `q` query parameter required just by not declaring a default value, like:

```Python
q: str
```

instead of: