@app.route('/log', methods=['GET', 'POST'])
def log():
    if current_user.is_authenticated:
        return redirect(url_for('view'))
    form=Form(request.form)
    error=None
    if request.method == 'POST' and form.validate():
        femail = request.form['email']
        password=request.form['password']
        user = User.query.filter_by(email=femail).first()
        if user is None or not user.check_password(password):
            error = 'Invalid username or password.'
            flash(error)
            return redirect(url_for('log'))
        login_user(user)
        return redirect(url_for('view'))
    return render_template('login.html', error=error, form=form)

class User(db.Model,UserMixin):
    __tablename__="user"
    id = db.Column(db.Integer, primary_key=True)
    email = db.Column(db.String(255), unique=True)
    password = db.Column(db.String(255))
    confirmed_at = db.Column(db.DateTime())
    roles = db.relationship(
        'Role',
        secondary=roles_users,
        backref=db.backref('user', lazy='dynamic')
    )
    posts = db.relationship('Post', backref='author', lazy='dynamic')


    def set_password(self, password):
        self.password_hash = generate_password_hash(password)

    def check_password(self, password):
        return check_password_hash(self.password_hash, password)

    def is_authenticated(self):
        return True

<form  action="" method="post" role="form">
{{ form.csrf }}
    <div class="login">
    <div class="login-screen">
        <div class="app-title">
            <h1>Login</h1>
        </div>
        <div class="login-form">

            <div class="control-group">
            <input type="text" class="login-field" value="" placeholder="email" name="email">
            <label class="login-field-icon fui-user" for="login-name"></label>
            </div>

            <div class="control-group">
            <input type="password" class="login-field" value="" placeholder="password" name="password">
            <label class="login-field-icon fui-lock" for="login-pass"></label>
            </div>

            <input type="submit" value="Log in" class="btn btn-primary btn-large btn-block" >

            {% if error %}
        <p><strong>Error:</strong> {{ error }}
        {% endif %}
            <br>
        </div>
    </div>
</div>