bound formでwidgetを変更する

view.pyでお決まりの呪文に追加

if request.method == u'POST':
    form = FooForm(request.POST, instance=Foo)
    form.fields['fieldName'].widget=PasswordInput()
    if form.is_valid():
    .........
else:
    form = FooForm(instance=Foo)
    form.fields['fieldName'].widget=PasswordInput()