How to use the flasgger.fields.Str function in flasgger

and will extract the schema from `in: body` definition
    and the data will default to `request.json`

    or you can specify:
    @swag_from('file.yml',
               validation=True,
               definition='User',
               data=lambda: request.json,  # any callable
               )
    """
    data = request.json
    return jsonify(data)


class User(Schema):
    username = fields.Str(required=True, default="Sirius Black")
    # wrong default "180" to force validation error
    age = fields.Int(required=True, min=18, default="180")
    tags = fields.List(fields.Str(), default=["wizard", "hogwarts", "dead"])


class UserPostView(SwaggerView):
    tags = ['users']
    parameters = User
    responses = {
        200: {
            'description': 'A single user item',
            'schema': User
        }
    }
    validation = True

"""
Example using Marshmallow Schema and fields as definitions
"""
# coding: utf-8
from flask import Flask, jsonify

from flasgger import Schema, Swagger, SwaggerView, fields


class Color(Schema):
    name = fields.Str()


class Palette(Schema):
    pallete_name = fields.Str()
    colors = fields.Nested(Color, many=True)


class PaletteView(SwaggerView):
    parameters = [
        {
            "name": "palette",
            "in": "path",
            "type": "string",
            "enum": ["all", "rgb", "cmyk"],
            "required": True,
            "default": "all"
        }
    ]
    # definitions = {'Palette': Palette, 'Color': Color}
    responses = {