Python Tips: Getting Data from a Flask Request

To retrieve data received in a Flask request, you can use the following attributes available on the request object:

from flask import request

• request.args: This attribute contains the key/value pairs from the URL query string. You can access them using request.args['key'].
• request.form: This attribute contains the key/value pairs from the body of an HTML post form or a JavaScript request that isn’t JSON encoded. You can access them using request.form['key'].
• request.files: If your request includes files in the body, Flask keeps them separate from the form data. HTML forms must use enctype=multipart/form-data for file uploads. You can access the files using request.files['key'].
• request.values: This attribute combines the args and form attributes, giving preference to args if there are overlapping keys. You can access the values using request.values['key'].
• request.json: If the request contains JSON data and has the application/json content type, you can access the parsed JSON data using request.json. Alternatively, you can use request.get_json(force=True) to ignore the content type.

All of these attributes are instances of MultiDict from the Werkzeug library, except for json. To access values from the MultiDict, you can use the following methods:

• request.form['name']: Use indexing if you know the key exists.
• request.form.get('name'): Use the get method if the key might not exist.
• request.form.getlist('name'): Use the getlist method if the key is sent multiple times and you want a list of values. The get method only returns the first value.

In most common cases, request.data will be empty as it is used as a fallback when Flask encounters a mime-type it doesn’t handle.

For more details, you can refer to the Flask documentation on the request object.