How to create a registration form in django that will recognise when password and confirm password don't match

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Python

forms

Django

I am trying to build a registration form for a user on a webpage using python and the Django framework. The form works fine and registers a user if all the fields are valid and Django has built in error messages if fields are left blank etc which work fine. However, I am trying to add my own error for if the 'password' and 'confirm password' fields don't match. If they don't match I get an error stating: 'The view main.views.register didn't return an HttpResponse object. It returned None instead.' My question is how would I successfully return the registration page with the error displayed to the user?

Here is my views.py code:

def register(request):
    if request.method == "GET":
        register_form = RegisterForm()
        return render(request, "main/register.html", {
            'form': register_form
        })
    else:
        register_form = RegisterForm(request.POST)
        if register_form.is_valid():
            register_form.save()
            return render(request, "main/login.html")

and here is my forms.py code:

class RegisterForm(forms.ModelForm):
    password = forms.CharField(widget=forms.PasswordInput())
    confirm_password = forms.CharField(widget=forms.PasswordInput())
    class Meta:
        model = User
        fields = ['first_name', 'last_name', 'username', 'email', 'password']
    def clean(self):
        cleaned_data = super(RegisterForm, self).clean()
        password = cleaned_data.get("password")
        confirm_password = cleaned_data.get("confirm_password")

        if password != confirm_password:
        
            self.add_error("confirm_password", "Password does not match")

What I have tried:

I have tried rendering the register webpage after submission, but I can't work out how to render it with my added errors