I had a quick read of https://docs.djangoproject.com/en/1.4/ref/forms/widgets/
which rabbited on about widgets – apparently they are
Django’s representation of a HTML input element. The widget handles the rendering of the HTML
and then each form field is tied to a widget – have a read of:
https://docs.djangoproject.com/en/1.4/ref/forms/fields/#built-in-fields
for the ChoiceField, the defaultWidget is “Select” (as noted in the above link). Ok, knowing the right widget, to add the class i just needed:
widget=forms.Select(attrs={'class':'regDropDown'})
so that my final line ended up reading:
gender = ChoiceField(label="", choices=SEX, widget=forms.Select(attrs={'class':'regDropDown'}))
Huzzah!