Custom form validation

I have a pretty simple form:

from django import forms

class InitialSignupForm(forms.Form):
    email = forms.EmailField()
    password = forms.CharField(max_length=255, widget = forms.PasswordInput)
    password_repeat = forms.CharField(max_length=255, widget = forms.PasswordInput)

    def clean_message(self):
        email = self.clean_data.get('email', '')
        password = self.clean_data.get('password', '')
        password_repeat = self.clean_data.get('password_repeat', '')

        try:
            User.objects.get(email_address = email)
            raise forms.ValidationError("Email taken.")
        except User.DoesNotExist:
            pass

        if password != password_repeat:
            raise forms.ValidationError("The passwords don't match.")

Is this how custom form validation is done? I need to evaluate on email that no users currently exist with that email address. I also need to evaluate that password and password_repeat match. How can I go about doing this?

To validate a single field on it's own you can use a clean_FIELDNAME() method in your form, so for email:

def clean_email(self):
    email = self.cleaned_data['email']
    if User.objects.filter(email=email).exists():
        raise ValidationError("Email already exists")
    return email

then for co-dependant fields that rely on each other, you can overwrite the forms clean() method which is run after all the fields (like email above) have been validated individually:

def clean(self):
    form_data = self.cleaned_data
    if form_data['password'] != form_data['password_repeat']:
        self._errors["password"] = ["Password do not match"] # Will raise a error message
        del form_data['password']
    return form_data

I'm not sure where you got clean_message() from, but that looks like it is a validation method made for a message field which doesn't seem to exist in your form.

Have a read through this for more details:

https://docs.djangoproject.com/en/dev/ref/forms/validation/