django check if user already exists code example

Example: check if username exists in database django

class FormClass:
	username = ...
	def clean(self):
		super(FormClass, self).clean()
    	username = self.cleaned_data['username']
    	if User.objects.exclude(pk=self.instance.pk).filter(username=username).exists():
        	raise forms.ValidationError(f'Username "{username}" is already in use.')
    	return username