Py Flask-WTF.py

# basic login form

    # main.py
    
        from flask import Flask, render_template
        from flask_wtf import FlaskForm
        from wtforms import StringField, PasswordField, SubmitField
    
    
        class LoginForm(FlaskForm):
            email = StringField(label='Email')
            password = PasswordField(label='Password')
            submit = SubmitField(label="Log in")
        
        app = Flask(__name__)
        app.secret_key = "test-secret"
        
        @app.route("/")
        def home():
            return render_template('index.html')
        
        @app.route("/login")
        def login():
            login_form = LoginForm()
            return render_template('login.html', form=login_form)
        
        if __name__ == '__main__':
            app.run(debug=True)
        
        
    # login.html
        ...
                <form method="POST" action="{{ url_for('login') }}">
                    {{ form.csrf_token }}
                    {{ form.email.label }} {{ form.email(size=30) }}
                    {{ form.password.label }} {{ form.password(size=30) }}
                    {{ form.submit }}
                </form>
        ...
        
        
        
        
        
# login form with input validation (email format and password length)

    # main.py
        from flask import Flask, render_template
        from flask_wtf import FlaskForm
        from wtforms import StringField, PasswordField, SubmitField
        from wtforms.validators import DataRequired, Email, Length
        
        
        
        class LoginForm(FlaskForm):
            email = StringField(label='Email', validators=[DataRequired(), Email()])
            password = PasswordField(label='Password', validators=[DataRequired(), Length(8)])
            submit = SubmitField(label="Log in")
        
        app = Flask(__name__)
        app.secret_key = "test-secret"
        
        @app.route("/")
        def home():
            return render_template('index.html')
        
        @app.route("/login", methods=["GET", "POST"])
        def login():
            login_form = LoginForm()
            if login_form.validate_on_submit():
                email_reference = "admin@email.com"
                pw_reference = "12345678"
                if (login_form.email.data == email_reference and login_form.password.data == pw_reference):
                    return render_template('success.html')
                else:
                    return render_template('denied.html')
            return render_template('login.html', form=login_form)
        
        if __name__ == '__main__':
            app.run(debug=True)    
    #login..html
        ...
            <form method="POST" action="{{ url_for('login') }}" novalidate>
                {{ form.csrf_token }}
                <p>
                    {{ form.email.label }} <br> {{ form.email(size=30) }}
                    {% for err in form.email.errors %}
                    <span style="color:red">{{ err }}</span>
                    {% endfor %}
                </p>
                <p>
                    {{ form.password.label }} <br> {{ form.password(size=30) }}
                    {% for err in form.password.errors %}
                    <span style="color:red">{{ err }}</span>
                    {% endfor %}
                </p>
                {{ form.submit }}
            </form>
        ...
        
        
        
        
# if combined with Bootstrap, it is possible to simplify the code in the HTML file
# https://pythonhosted.org/Flask-Bootstrap/basic-usage.html

    {% extends 'bootstrap/base.html' %}
    {% import "bootstrap/wtf.html" as wtf %}
    ...
        {{ wtf.quick_form(form) }} # 'novalidate=True' as second parameter, to turn off the default validation check done by some browsers
    ...
    
    
    
    
# Form with dropdown list selection
    
    # main.py
        from wtforms import  SelectField
        
        ...
        
        class CafeForm(FlaskForm):
            coffee_rating = SelectField("Coffee Rating", choices=["☕️", "☕☕", "☕☕☕", "☕☕☕☕", "☕☕☕☕☕"], validators=[DataRequired()])