from flask_wtf import Form
from wtforms import StringField, PasswordField
from wtforms.validators import DataRequired


class LoginForm(Form):

    username = StringField('Username', validators=[DataRequired()])
    password = PasswordField('Password', validators=[DataRequired()])

from flask import request
form = LoginForm(request.form)

class StringField(Field):
    """
    This field is the base for most of the more complicated fields, and
    represents an ``<input type="text">``.
    """
    widget = widgets.TextInput()

    def process_formdata(self, valuelist):
        if valuelist:
            self.data = valuelist[0]
        else:
            self.data = ''

    def _value(self):
        return text_type(self.data) if self.data is not None else ''

self.data = valuelist[0]