覆盖python中的函数

Question

I have the following base class (code shortened):

class SignupForm(GroupForm):

    username = forms.CharField(
        label = _("Username"),
        max_length = 30,
        widget = forms.TextInput()
    )

    def __init__(self, *args, **kwargs):
        super(SignupForm, self).__init__(*args, **kwargs)
        if REQUIRED_EMAIL or EMAIL_VERIFICATION or EMAIL_AUTHENTICATION:
            self.fields["email"].label = ugettext("Email")
            self.fields["email"].required = True
        else:
            self.fields["email"].label = ugettext("Email (optional)")
            self.fields["email"].required = False


    def after_signup(self, user, **kwargs):
        """
        An extension point for subclasses.
        """
        pass

What I wanna do is override the after_signup() function and the username field like so:

class CompanySignupForm(SignupForm):
    #TODO: override fields for company signup form

    username = forms.CharField(
        label = _("Username TEST"),
        max_length = 30,
        widget = forms.TextInput()
    )

    def after_signup(self, user, **kwargs):
        """
        An extension point for subclasses.
        """
        print str('after_signup is has been overwritten')

My Problem: Only the username field shows the desired behavior. The after_signup() function get never called. Instead the after_signup() function of the base class SignupForm gets called. What am I doning wrong?

EDIT:

the imports: 
from django import forms 
from django.contrib.auth.models import User 
from django.utils.translation import ugettext_lazy as _, ugettext

instantiating CompanySignupForm:

url(r"^signup/$", CompanySignupForm.as_view(), name="acct_signup")

after_signup() is beeing called from a function in the base class:

def save(self, request=None): 
    # more code here
    # ...
    self.after_signup(new_user)

Answer 1

Use isinstance() to check an instance's type and .__class__ to make sure you are instantiating CompanySignupForm .

Also you might want to create an __init__ method on the CompanySignupForm to ensure it's not just instantiating the super class.

Note: Reading your edit more closely your not calling after_signup directly the base class function save is right? This will then call it's local method after_signup if it exists. I'd take that function out of the base class and force it to call the inherited functions

To check the version run:

signup = CompanySignupForm.as_view()
print signup.__class__

url(r"^signup/$", signup, name="acct_signup")