3.3 KiB
Form Data
When you need to receive form fields instead of JSON, you can use Form.
/// info
To use forms, first install python-multipart.
Make sure you create a virtual environment{.internal-link target=_blank}, activate it, and then install it, for example:
$ pip install python-multipart
///
Import Form
Import Form from fastapi:
//// tab | Python 3.9+
{!> ../../docs_src/request_forms/tutorial001_an_py39.py!}
////
//// tab | Python 3.8+
{!> ../../docs_src/request_forms/tutorial001_an.py!}
////
//// tab | Python 3.8+ non-Annotated
/// tip
Prefer to use the Annotated version if possible.
///
{!> ../../docs_src/request_forms/tutorial001.py!}
////
Define Form parameters
Create form parameters the same way you would for Body or Query:
//// tab | Python 3.9+
{!> ../../docs_src/request_forms/tutorial001_an_py39.py!}
////
//// tab | Python 3.8+
{!> ../../docs_src/request_forms/tutorial001_an.py!}
////
//// tab | Python 3.8+ non-Annotated
/// tip
Prefer to use the Annotated version if possible.
///
{!> ../../docs_src/request_forms/tutorial001.py!}
////
For example, in one of the ways the OAuth2 specification can be used (called "password flow") it is required to send a username and password as form fields.
The spec requires the fields to be exactly named username and password, and to be sent as form fields, not JSON.
With Form you can declare the same configurations as with Body (and Query, Path, Cookie), including validation, examples, an alias (e.g. user-name instead of username), etc.
/// info
Form is a class that inherits directly from Body.
///
/// tip
To declare form bodies, you need to use Form explicitly, because without it the parameters would be interpreted as query parameters or body (JSON) parameters.
///
About "Form Fields"
The way HTML forms (<form></form>) sends the data to the server normally uses a "special" encoding for that data, it's different from JSON.
FastAPI will make sure to read that data from the right place instead of JSON.
/// note | "Technical Details"
Data from forms is normally encoded using the "media type" application/x-www-form-urlencoded.
But when the form includes files, it is encoded as multipart/form-data. You'll read about handling files in the next chapter.
If you want to read more about these encodings and form fields, head to the MDN web docs for POST.
///
/// warning
You can declare multiple Form parameters in a path operation, but you can't also declare Body fields that you expect to receive as JSON, as the request will have the body encoded using application/x-www-form-urlencoded instead of application/json.
This is not a limitation of FastAPI, it's part of the HTTP protocol.
///
Recap
Use Form to declare form data input parameters.