forms.py

from django import forms
from django.contrib.auth.models import User 
class RegisterForm(forms.Form):
    username = forms.CharField(label='Username', max_length=100)
    email = forms.EmailField(label='Email')
    password = forms.CharField(widget=forms.PasswordInput)
    password2 = forms.CharField(widget=forms.PasswordInput, label='Confirm password')

    def clean_username(self):
        username = self.cleaned_data.get('username')
        if User.objects.filter(username=username).exists():
            raise forms.ValidationError('Username is already taken')
        return username

    def clean_email(self):
        email = self.cleaned_data.get('email')
        if User.objects.filter(email=email).exists():
            raise forms.ValidationError('Email is already taken')
        return email

    def clean(self):
        cleaned_data = super().clean()
        password = cleaned_data.get('password')
        password2 = cleaned_data.get('password2')
        if password != password2:
            raise forms.ValidationError('Passwords do not match')