How can I validate forms in Flask using Flask-WTF?

How can I validate forms in Flask using Flask-WTF?

You can validate forms in Flask using the Flask-WTF extension, which integrates WTForms with Flask. It provides easy form handling and validation.

What are some common validation methods I can use?

Common validation methods include required fields, length checks, email format validation, and custom validators.

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

Sure! Here's a simple 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.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()

What if I want to add custom validation?

You can create a custom validator by defining a function and using it in your form field. For example:

def custom_length_check(form, field):
    if len(field.data) < 5:
        raise ValidationError('Field must be at least 5 characters long.')

class MyForm(FlaskForm):
    username = StringField('Username', validators=[DataRequired(), custom_length_check])