});

        ShareEnumIterator it = new ShareEnumIterator(parent, entries.iterator(), filter);

        // Returns only accepted resources
        assertTrue(it.hasNext());
        assertEquals("keep1/", it.next().getName());
        assertTrue(it.hasNext());
        assertEquals("keep2/", it.next().getName());
        assertFalse(it.hasNext());

        // Verify filter called once per entry

It used custom types in its declarations instead of standard Python types, but it was still a huge step forward.

It also was one of the first frameworks to generate a custom schema declaring the whole API in JSON.

It was not based on a standard like OpenAPI and JSON Schema. So it wouldn't be straightforward to integrate it with other tools, like Swagger UI. But again, it was a very innovative idea.

        // Act
        TestIterator it = TestIterator.create(tree, parent, wildcard, null, attrs, initial, pages);

        // Assert
        assertSame(tree, it.getTreeHandle(), "tree handle should be same instance returned by acquire");
        assertEquals(attrs, it.getSearchAttributes());
        assertEquals(wildcard, it.getWildcard());
        assertSame(parent, it.getParent());
        verify(tree, times(1)).acquire();

                            os to (testProject to performanceTestDuration)
                        }
                }
            }
        return pairs
            .groupBy({ it.first }, { it.second })
            .mapValues { entry -> entry.value.groupBy({ it.first }, { it.second }) }
    }

    private fun readPerformanceTestConfigurations(performanceTestsCiJson: File): List<PerformanceTestConfiguration> {

Let's use the tools provided by **FastAPI** to handle security.

## How it looks { #how-it-looks }

Let's first just use the code and see how it works, and then we'll come back to understand what's happening.

## Create `main.py` { #create-main-py }

Copy the example in a file `main.py`:

{* ../../docs_src/security/tutorial001_an_py39.py *}

## Run it { #run-it }

/// info

* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.
* Then it passes the **request** to be processed by the rest of the application (by some *path operation*).

It might be useful, for example, to return custom headers or cookies.

## Return a `Response` { #return-a-response }

In fact, you can return any `Response` or any sub-class of it.

/// tip

`JSONResponse` itself is a sub-class of `Response`.

///

And when you return a `Response`, **FastAPI** will pass it directly.

```JSON
{
    "name": "Foo",
    "price": 45.2
}
```

## Declare it as a parameter { #declare-it-as-a-parameter }

To add it to your *path operation*, declare it the same way you declared path and query parameters:

{* ../../docs_src/body/tutorial001_py310.py hl[16] *}

...and declare its type as the model you created, `Item`.

/// tip

...Although if the whole application is just **crashing immediately** it probably doesn't make sense to keep restarting it forever. But in those cases, you will probably notice it during development, or at least right after deployment.

So let's focus on the main cases, where it could crash entirely in some particular cases **in the future**, and it still makes sense to restart it.

///

But that's not the only way to declare dependencies (although it would probably be the more common).

The key factor is that a dependency should be a "callable".

A "**callable**" in Python is anything that Python can "call" like a function.

So, if you have an object `something` (that might _not_ be a function) and you can "call" it (execute it) like:

```Python
something()
```

or

```Python