Why can not initialize the class?

[Steven D'Aprano]

Luofeiyu, you are getting stuck on basic questions. Before working with
advanced features like properties, you should learn the simply features.


luofeiyu wrote:

> >>> class Contact(object):
> ...     def __init__(self, first_name=None, last_name=None,
> ...                  display_name=None, email="haha at haha"):
> ...         self.first_name = first_name
> ...         self.last_name = last_name
> ...         self.display_name = display_name
> ...         self.email = email
> ...     def print_info(self):
> ...         print(self.display_name, "<" + self.email + ">"  )
> ...     def set_email(self, value):
> ...         print(value)
> ...         self._email = value
> ...     def get_email(self):
> ...         return self._email
> ...     email = property(get_email, set_email)
> ...
>  >>>
>  >>> contact = Contact()
> haha at haha
> 
> why the value in `def set_email(self, value): `  is  haha at haha?
> how haha at haha  is called to  value in `def set_email(self, value): `?
> would you mind telling me the process?

Instead of this complicated example, start with this simple example:

class Contact(object):
    def __init__(self, email="haha at haha"):
        self.email = email

contact = Contact()
print(contact.email)


Do you understand how contact.email gets set to "haha at haha"?


Now let's make it a bit more complicated:

class Contact(object):
    def __init__(self, email="haha at haha"):
        self.set_email(email)
    def set_email(self, value):
        self.email = value

contact = Contact()
print(contact.email)


Do you still understand how contact.email gets set to "haha at haha"?


One final version:

class Contact(object):
    def __init__(self, email="haha at haha"):
        self.email = email
    def _get_email(self):
        return self._the_secret_private_email
    def _set_email(self, value):
        self.self._the_secret_private_email = value
    email = property(_get_email, _set_email)

contact = Contact()
print(contact.email)


Now do you understand how contact.email gets set to "haha at haha"?



-- 
Steven