Python Getter/Setter Question

Nexusfactor · 06-02-2015, 09:18 AM

I was doing some reading here, and the author is discussing getter/setters in python. He compares the concept with Java.

Near the end he does this:

Code:

class Contact(object):

    def __init__(self, first_name=None, last_name=None, 
                 display_name=None, email=None):
        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):
        if '@' not in value:
            raise Exception("This doesn't look like an email address.")
        self._email = value

    def get_email(self):
        return self._email

    email = property(get_email, set_email)

Implements getter/setters, with a exception in the setter property. So far I get it.

Then he proceeds to say, what NOT to do, and demonstrates this:

Code:

class Contact(object):

    def __init__(self, first_name=None, last_name=None, 
                 display_name=None, email=None):
        self.set_first_name(first_name)
        self.set_last_name(last_name)
        self.set_display_name(display_name)
        self.set_email(email)

    def set_first_name(self, value):
        self._first_name = value

    def get_first_name(self):
        return self._first_name

    def set_last_name(self, value):
        self._last_name = value

    def get_last_name(self):
        return self._last_name

    def set_display_name(self, value):
        self._display_name = value

    def get_display_name(self):
        return self._display_name

    def set_email(self, value):
        self._email = value

    def get_email(self):
        return self._email

    def print_info(self):
        print self.display_name, "<" + self.email + ">"

However, besides the exception, isn't that what you did in your previous code above? I'm I missing something? The author implements the email getter/setter methods, and then proceeds to say in the code at the bottom, don't do it that way.

What should be done? How would a python programmer handle creating the contact class with getter/setter properties?

Myk267 · 06-02-2015, 10:37 AM

Did you read the article? Look under "The Brush and The Canvas" for more details about why you shouldn't use that second style in your post. Even if you don't read the article, the second one is much longer and verbose and offers nothing more than the first.

Nexusfactor · 06-02-2015, 11:17 AM

I did read the article, but I couldn't fully understand it. Thanks for the explanation anyways

Much appreciated.

If I write my classes the way the author specifies is proper practice:

Code:

class Contact(object):

    def __init__(self, first_name=None, last_name=None, 
                 display_name=None, email=None):
        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):
        if '@' not in value:
            raise Exception("This doesn't look like an email address.")
        self._email = value

    def get_email(self):
        return self._email

    email = property(get_email, set_email)

First, how then would the exception be raised if I create my object using the constructor? He no longer calls the set property from the constructor, which he says NOT to do.

Secondly, Why didn't he use property decorators? Wouldn't that be a better option?

Forgive me, I new to Python, and I'm just trying to wrap my head around certain concepts.

dugan · 06-02-2015, 11:37 AM

The only explanation I could imagine is that the property decorator might not have been available back then. You are correct that today, it would be written like this:

Code:

class Contact(object):

    def __init__(self, first_name=None, last_name=None, 
                 display_name=None, email=None):
        self.first_name = first_name
        self.last_name = last_name
        self.display_name = display_name

         # This calls the setter property.
        self.email = email

    def print_info(self):
        print self.display_name, "<" + self.email + ">"            

    @property
    def email(self):
        return self._email

    @email.setter
    def email(self, value):
        if '@' not in value:
            raise Exception("This doesn't look like an email address.")
        self._email = value