How can I implement form validation in Flask using WTForms?

How can I implement form validation in Flask using WTForms?

You can use Flask-WTF, which integrates WTForms with Flask. First, install Flask-WTF using pip.

What are some common validation methods I can use?

Common validation methods include DataRequired, Email, Length, and Regexp. You can apply them to your form fields.

Can you show me a simple example of a form with validation?

Sure! Here's a basic example:

from flask import Flask, render_template, redirect, url_for
from flask_wtf import FlaskForm
from wtforms import StringField, SubmitField
from wtforms.validators import DataRequired, Email

app = Flask(__name__)
app.config['SECRET_KEY'] = 'your_secret_key'

class MyForm(FlaskForm):
    email = StringField('Email', validators=[DataRequired(), Email()])
    submit = SubmitField('Submit')

@app.route('/', methods=['GET', 'POST'])
def index():
    form = MyForm()
    if form.validate_on_submit():
        return redirect(url_for('success'))
    return render_template('index.html', form=form)

@app.route('/success')
def success():
    return 'Form submitted successfully!'

if __name__ == '__main__':
    app.run(debug=True)

What if the form validation fails?

If validation fails, Flask-WTF will automatically populate the form with error messages, which you can display in your template.