But we want to be able to parameterize that fixed content.

## A "callable" instance { #a-callable-instance }

In Python there's a way to make an instance of a class a "callable".

Not the class itself (which is already a callable), but an instance of that class.

To do that, we declare a method `__call__`:

{* ../../docs_src/dependencies/tutorial011_an_py39.py hl[12] *}

    // HcHttpClient.AUTHENTICATIONS_PROPERTY,
    // basicAuthList.toArray(new Authentication[basicAuthList.size()]));
    //
    // List<Callable<ResponseData>> list =
    // new ArrayList<Callable<ResponseData>>();
    // for (int i = 0; i < 100; i++) {
    // list.add(new Callable<ResponseData>() {
    // public ResponseData call() throws Exception {
    // String[] urls =
    // new String[] {
    // "http://.../",

So, a Python class is also a **callable**.

Then, in **FastAPI**, you could use a Python class as a dependency.

What FastAPI actually checks is that it is a "callable" (function, class or anything else) and the parameters defined.

        }
    }

    /**
     * Execute a callable through the circuit breaker
     *
     * @param <T> return type
     * @param callable the callable to execute
     * @return the result
     * @throws Exception if execution fails or circuit is open
     */
    public <T> T call(Callable<T> callable) throws Exception {
        return call(callable, null);
    }

    /**

///

The `oauth2_scheme` variable is an instance of `OAuth2PasswordBearer`, but it is also a "callable".

It could be called as:

```Python
oauth2_scheme(some, parameters)
```

So, it can be used with `Depends`.

### Use it { #use-it }

import org.apache.maven.api.annotations.Nullable;

/**
 * An XML reader request.
 *
 * @since 4.0.0
 */
@Experimental
@Immutable
public interface XmlReaderRequest {

    @Nullable
    Path getPath();

    @Nullable
    Path getRootDirectory();

    @Nullable
    URL getURL();

    @Nullable
    InputStream getInputStream();

    @Nullable
    Reader getReader();

    @Nullable

        } catch (Exception e) {
          future.completeExceptionally(e);
        }
      }

      @Override
      public void onEvent(@NotNull EventSource eventSource, @Nullable String id, @Nullable String type, @NotNull String data) {
        try {
          assertEquals("hello", data);
          future.complete(null);
        } catch (Exception e) {
          future.completeExceptionally(e);
        }

    TypeVariableInvocationHandler(TypeVariableImpl<?> typeVariableImpl) {
      this.typeVariableImpl = typeVariableImpl;
    }

    @Override
    public @Nullable Object invoke(Object proxy, Method method, @Nullable Object @Nullable [] args)
        throws Throwable {
      String methodName = method.getName();
      Method typeVariableMethod = typeVariableMethods.get(methodName);

   * @since 25.1
   */
  // TODO(diamondm) consider using Arrays.toString() for array parameters
  public static String lenientFormat(
      @Nullable String template, @Nullable Object @Nullable ... args) {
    template = String.valueOf(template); // null -> "null"

    if (args == null) {
      args = new Object[] {"(Object[])null"};
    }

* Fix support for callable class dependencies with `yield`. PR [#1365](https://github.com/tiangolo/fastapi/pull/1365) by [@mrosales](https://github.com/mrosales).