Create a new file called forms.py and insert the below code in there. Then your code should work.
from flask.ext.wtf import Form
from wtforms import TextField, TextAreaField, SubmitField, validators
class ContactForm(Form):
name = TextField("Name", [validators.Required()])
email = TextField("Email", [validators.Required(), validators.email()])
subject = TextField("Subject", [validators.Required()])
message = TextAreaField("Message", [validators.Required()])
submit = SubmitField("Send")