descriptors.py

# Simple (?) example of descriptor use in Python.

class FullName():
    def __get__(self, i, o):
        return '%s %s' % (i.first_name, i.last_name)


class LastName():
    def __get__(self, i, o):
        if i.married and i.gender == Person.female and i.spouse is not None:
            return i.spouse.text_last_name

        return i.text_last_name


class Person():
    male = 1
    female = 2
    last_name = LastName()

    def __init__(self, first_name, last_name, gender, married, spouse):
        self.first_name = first_name
        self.text_last_name = last_name
        self.gender = gender
        self.married = married
        self.spouse = spouse
        if spouse is not None:
            spouse.spouse = self
            
    def marry(spouse):
        # Let's assume same-sex marriage is cool.
        # and people don't change surnames in a same-sex marriage.
        self.married = True
        self.spouse = spouse
        
        # FIXME: This won't work in countries that support polygamy.
        self.spouse.spouse = self
        
    def divorce():
        self.married = False
        
        # FIXME: This won't work in countries that support polygamy.
        self.spouse.spouse = None
        self.spouse = None

# In [163]: jd = Person("John", "Doe", Person.male, True, None)
#
# In [164]: jf = Person("Jane", "Fonda", Person.female, True, jd)
#
# In [165]: jf.name
# Out[165]: 'Jane Doe'
#
# In [166]: jf.divorce()
#
# In [167]: jf.name
# Out[167]: 'Jane Fonda'
#
# In [168]: jf.marry(jd)
#
# In [169]: jf.name
# Out[169]: 'Jane Doe'