Then you could call that Python program:

<div class="termy">

```console
// Here we don't set the env var yet
$ python main.py

// As we didn't set the env var, we get the default value

Hello World from Python

// But if we create an environment variable first
$ export MY_NAME="Wade Wilson"

// And then call the program again
$ python main.py

        return True
    dunder_call = getattr(call, "__call__", None)  # noqa: B004
    return inspect.isasyncgenfunction(dunder_call)


def is_gen_callable(call: Callable[..., Any]) -> bool:
    if inspect.isgeneratorfunction(call):
        return True
    dunder_call = getattr(call, "__call__", None)  # noqa: B004
    return inspect.isgeneratorfunction(dunder_call)


async def solve_generator(

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
something(some_argument, some_keyword_argument="foo")
```

    All of them share the same parameters for additional validation and metadata you have seen.

!!! note "Technical Details"
    When you import `Query`, `Path` and others from `fastapi`, they are actually functions.

    That when called, return instances of classes of the same name.

```

Das war's.

Das sind die „Typhinweise“:

```Python hl_lines="1"
{!../../../docs_src/python_types/tutorial002.py!}
```

Das ist nicht das gleiche wie das Deklarieren von Defaultwerten, wie es hier der Fall ist:

```Python
    first_name="john", last_name="doe"
```

Das ist eine andere Sache.

Wir verwenden Doppelpunkte (`:`), nicht Gleichheitszeichen (`=`).

With that, we can just call `crud.get_user` directly from inside of the *path operation function* and use that session.

!!! tip
    Notice that the values you return are SQLAlchemy models, or lists of SQLAlchemy models.

An example could be that you have an external authentication provider that you need to call.

You send it a token and it returns an authenticated user.

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.

            if security_definitions:
                security_schemes.update(security_definitions)
            all_route_params = get_flat_params(route.dependant)
            operation_parameters = get_openapi_operation_parameters(
                all_route_params=all_route_params,
                schema_generator=schema_generator,
                model_name_map=model_name_map,

---

## Install FastAPI

The first step is to install FastAPI.

For the tutorial, you might want to install it with all the optional dependencies and features:

<div class="termy">

```console
$ pip install "fastapi[all]"

---> 100%
```

</div>

Sie möchten den externen Anbieter wahrscheinlich einmal testen, ihn aber nicht unbedingt bei jedem weiteren ausgeführten Test aufrufen.

In diesem Fall können Sie die Abhängigkeit, die diesen Anbieter aufruft, überschreiben und eine benutzerdefinierte Abhängigkeit verwenden, die einen Scheinbenutzer zurückgibt, nur für Ihre Tests.