def validate(self, extra_validators=None):
    """
    Validates the form by calling `validate` on each field.

    :param extra_validators:
        If provided, is a dict mapping field names to a sequence of
        callables which will be passed as extra validators to the field's
        `validate` method.

    Returns `True` if no errors occur.
    """
    self._errors = None
    success = True
    for name, field in iteritems(self._fields):
        if extra_validators is not None and name in extra_validators:
            extra = extra_validators[name]
        else:
            extra = tuple()
        if not field.validate(self, extra):
            success = False
    return success

from wtforms import StringField, BooleanField, PasswordField, validators, ValidationError, HiddenField
from flask_wtf import Form

class LoginForm(RedirectForm):
email = StringField('Email', [
    validators.DataRequired(),
    validators.Email('Invalid Email Address')
])

password = PasswordField('Password', [
    validators.DataRequired()
])

def validate(self):
    if not Form.validate(self):
        return False

    user = User.query.filter_by(email=self.email.data.lower()).first()
    if user and user.check_password(self.password.data):
        self.user = user
        return True
    else:
        self.email.errors.append("Invalid e-mail or password")

    return False

def get_user(self):
    return self.user