1. Introduction

In this tutorial, we're going to learn how to customize form error messages in Django. This is useful when you want to display more user-friendly messages, or when you want to display messages in a different language than the default English.

By the end of this tutorial, you'll be able to define custom error messages for your form fields, handle multiple error messages, and display them to the user in a way that suits your application.

This tutorial assumes you have a basic understanding of Python and Django. If you're new to Django, you might want to check out the official Django tutorial first.

2. Step-by-Step Guide

In Django, forms are used to collect and validate user input. When a form is invalid (e.g., a required field is empty), Django generates error messages that can be displayed to the user.

You can customize these error messages by setting the error_messages attribute on a form field. This attribute should be a dictionary where each key is the type of error and the value is the custom message.

3. Code Examples

Let's take a look at some examples. We'll start with a simple form with one field, and then see how we can customize its error messages.

from django import forms

class ContactForm(forms.Form):
    email = forms.EmailField()

    def clean_email(self):
        email = self.cleaned_data.get('email')
        if "gmail" not in email:
            raise forms.ValidationError("Please use a Gmail account.")
        return email

In this example, we define a form with an email field. We then override the clean_email method to add our custom validation: if the email doesn't contain "gmail", we raise a ValidationError with our custom error message.

If you try to submit this form with an invalid email, you'll see your custom error message.

4. Summary

In this tutorial, we learned how to customize form error messages in Django. We saw how to define custom error messages, display them to the user, and handle multiple error messages.

To continue learning about Django forms, you might want to check out the official documentation, which covers more advanced topics like formsets and model forms.

5. Practice Exercises

1. Create a form with a password field. Add a custom error message if the password is less than 8 characters long.
2. Create a form with a date field. Add a custom error message if the date is in the past.
3. Create a form with an integer field. Add two custom error messages: one if the number is less than 0, and another if the number is greater than 100.

Here are some tips for these exercises:
- Remember to use the ValidationError class to raise an error with your custom message.
- Use the clean_<fieldname> method to add your custom validation logic.
- Don't forget to return the cleaned data at the end of your clean_<fieldname> method.