If you pass a "callable" as a dependency in **FastAPI**, it will analyze the parameters for that "callable", and process them in the same way as the parameters for a *path operation function*. Including sub-dependencies.

That also applies to callables with no parameters at all. The same as it would be for *path operation functions* with no parameters.

# Header-Parameter { #header-parameters }

Sie können Header-Parameter genauso definieren, wie Sie `Query`-, `Path`- und `Cookie`-Parameter definieren.

## `Header` importieren { #import-header }

Importieren Sie zuerst `Header`:

{* ../../docs_src/header_params/tutorial001_an_py310.py hl[3] *}

## `Header`-Parameter deklarieren { #declare-header-parameters }

    // for error page

    /**
     * Query string parameter for error page fallback.
     * Contains the original search query if redirection fails.
     */
    public String q;

    /**
     * Number of results parameter for error page fallback.
     * Specifies how many results to display if redirection fails.
     */
    public String num;

    /**
     * Sort parameter for error page fallback.

    /**
     * Add the created action message for the key 'constraints.Size.message' with parameters.
     * <pre>
     * message: The size of {item} must be between {min} and {max}.
     * </pre>
     * @param property The property name for the message. (NotNull)
     * @param min The parameter min for message. (NotNull)
     * @param max The parameter max for message. (NotNull)
     * @return this. (NotNull)
     */

# Header Parameter Models { #header-parameter-models }

If you have a group of related **header parameters**, you can create a **Pydantic model** to declare them.

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`. 🤓

///

# Paramètres de chemin { #path-parameters }

Vous pouvez déclarer des « paramètres » ou « variables » de chemin avec la même syntaxe utilisée par les chaînes de format Python :

{* ../../docs_src/path_params/tutorial001_py310.py hl[6:7] *}

La valeur du paramètre de chemin `item_id` sera transmise à votre fonction dans l'argument `item_id`.

///

/// tip

To declare File bodies, you need to use `File`, because otherwise the parameters would be interpreted as query parameters or body (JSON) parameters.

///

The files will be uploaded as "form data".

If you declare the type of your *path operation function* parameter as `bytes`, **FastAPI** will read the file for you and you will receive the contents as `bytes`.

        </parameter>
        <parameter>
          <name>repositories</name>
          <type>java.util.List</type>
          <required>true</required>
          <editable>false</editable>
        </parameter>
        <parameter>
          <name>resourceBundles</name>
          <type>java.util.List</type>
          <required>true</required>
          <editable>true</editable>
        </parameter>
        <parameter>

    }
    Method method = (Method) member;
    if (!method.getName().contentEquals("equals")) {
      return false;
    }
    Class<?>[] parameters = method.getParameterTypes();
    if (parameters.length != 1) {
      return false;
    }
    if (!parameters[0].equals(Object.class)) {
      return false;
    }
    return true;
  }

# Paramètres de cookie { #cookie-parameters }

Vous pouvez définir des paramètres de cookie de la même manière que vous définissez les paramètres `Query` et `Path`.

## Importer `Cookie` { #import-cookie }

Commencez par importer `Cookie` :

{* ../../docs_src/cookie_params/tutorial001_an_py310.py hl[3] *}

## Déclarer des paramètres `Cookie` { #declare-cookie-parameters }