# Query Parameters and String Validations { #query-parameters-and-string-validations }

**FastAPI** allows you to declare additional information and validation for your parameters.

Let's take this application as example:

{* ../../docs_src/query_params_str_validations/tutorial001_py310.py hl[7] *}

 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    # o isAvailableDatabaseNativeJDBC: (NotRequired - Default false)
    #   [true]
    #     Use classes of database native JDBC on generated classes to get best performances of DB access.
    #     Your project needs to refer to database native JDBC.
    #
    #; isAvailableDatabaseNativeJDBC = false
    # - - - - - - - - - -/

    # /- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

The same example from above, returning an `HTMLResponse`, could look like:

{* ../../docs_src/custom_response/tutorial003_py39.py hl[2,7,19] *}

/// warning

```Python
from myapp import app
```

#### Pour davantage de détails

Imaginons que votre fichier s'appelle `myapp.py`.

Si vous l'exécutez avec :

<div class="termy">

```console
$ python myapp.py
```

</div>

alors la variable interne `__name__` de votre fichier, créée automatiquement par Python, aura pour valeur la chaîne de caractères `"__main__"`.

Ainsi, la section :

var errEtcdUnreachable = errors.New("etcd is unreachable, please check your endpoints")

func etcdErrToErr(err error, etcdEndpoints []string) error {
	if err == nil {
		return nil
	}
	switch err {
	case context.DeadlineExceeded:
		return fmt.Errorf("%w %s", errEtcdUnreachable, etcdEndpoints)
	default:
		return fmt.Errorf("unexpected error %w from etcd, please check your endpoints %s", err, etcdEndpoints)
	}
}

/// tip

First try with `bump-pydantic`, if your tests pass and that works, then you're done in one command. ✨

///

If `bump-pydantic` doesn't work for your use case, you can use the support for both Pydantic v1 and v2 models in the same app to do the migration to Pydantic v2 gradually.

You could fist upgrade Pydantic to use the latest version 2, and change the imports to use `pydantic.v1` for all your models.

        »»»

    Source (English):

        «««
        ### Run Your Program { #run-your-program }
        »»»

    Translate with (German):

        «««
        ### Ihr Programm ausführen { #run-your-program }
        »»»

    Do NOT translate with (German):

        «««
        ### Führen Sie Ihr Programm aus { #run-your-program }
        »»»

Most of these ideas would be more or less **independent**, and in most cases you should only need to study them if they apply directly to **your project**.

If something seems interesting and useful to your project, go ahead and check it, but otherwise, you might probably just skip them.

/// tip

Et les sections suivantes supposent que vous l'avez lu et que vous en connaissez les idées principales.

## Cours TestDriven.io