Custom Username Validation in Registration Form

This code defines a custom form validation function `validate_username` that checks if the username is alphanumeric and raises a validation error if it is not. It also defines a form class `RegistrationForm` that includes a username field using the `validate_username` function for validation.

Technology Stack : wtforms

Code Type : Custom form validation function

Code Difficulty : Intermediate

                
                    
from wtforms import Form, StringField, validators

def validate_username(form, field):
    if not field.data.isalnum():
        raise validators.ValidationError('Username must be alphanumeric.')

class RegistrationForm(Form):
    username = StringField('Username', [validate_username])

# JSON representation