索引或大小为负数，或大于允许值。(Index or size was negative, or greater than the allowed value.)

 是的，你可以在你的视图函数中动态地做到这一点。 
 
 文档中有一个例子，您可以按照以下方式进行修改： 
 
from flask import render_template, request
from flask_wtf import Form
from wtforms import BooleanField

json_data = [{'Description':'Red', 'id':'f1'}, 
             {'Description':'Green', 'id':'f2'}, 
             {'Description':'Blue', 'id':'f3'}]


@app.route('/taggs', methods = ['GET', 'POST'])
def taggs():
    class CustomForm(Form):
        pass

    for item in json_data:
        setattr(CustomForm, item["id"], 
                BooleanField(item["description"], id=item["id"]))

    form = CustomForm(request.form)

    return render_template('taggs.html', form=form)

Yes, you can do this dynamically in your view function.
 
The docs have an example of this, which you can adapt along the lines of:
 
from flask import render_template, request
from flask_wtf import Form
from wtforms import BooleanField

json_data = [{'Description':'Red', 'id':'f1'}, 
             {'Description':'Green', 'id':'f2'}, 
             {'Description':'Blue', 'id':'f3'}]


@app.route('/taggs', methods = ['GET', 'POST'])
def taggs():
    class CustomForm(Form):
        pass

    for item in json_data:
        setattr(CustomForm, item["id"], 
                BooleanField(item["description"], id=item["id"]))

    form = CustomForm(request.form)

    return render_template('taggs.html', form=form)