Alter python descriptor

Question

I've this python descriptor:

# Date Descriptor
class DateAttribute():
    def __init__(self, value=None):
        self.value = value
    def __get__(self, instance, value):
        return self.value
    def __set__(self, instance, value):
        if type(value) is not datetime.date: 
            raise TypeError('A date value is expected')
        self.value = value

and a class D that use this descriptor:

class D:
    thisdate = DateAttribute()

I use this class as:

x = D()
x.thisdate = datetime.date(2012, 9, 12)

I wish to extend the descriptor to give me formatted results in some ways. Es.

x.thisdate.format1
>>> '2012 9 12'
x.thisdate.format2
>>> '2012___9___12'
x.thisdate.format3
>>> '2012####9####12'
.....

I could do this ?

Thanks

Answer 1

Add the formatX properties to your class and format accordingly:

class DateAttribute:
    ...

    @property
    def format1 (self): return self.value.strftime (SOMEFORMAT)

    @property
    def format2 (self): return self.value.strftime (SOMEOTHERFORMAT)

For the strftime format strings, see the datetime documentation.

Works like this:

thisdate = DateAttribute (datetime.date (2012, 9, 12) )
print (thisdate.format1)

EDIT:

#! /usr/bin/python3

import datetime

class DateAttribute:
    def __init__(self, value=None):
        print ('initing')
        self.value = value

    def __get__(self, instance, value):
        print ('getting')
        if not self.value: return self.value
        return FormattedDate (self.value.year, self.value.month, self.value.day)

    def __set__(self, instance, value):
        print ('setting')
        if not isinstance (value, datetime.date): raise TypeError('A date value is expected')
        self.value = value


class FormattedDate (datetime.date):
    @property
    def format1 (self): return self.strftime ('%Y==%m==%d')

class D:
    thisdate = DateAttribute ()

d = D ()
print (d.thisdate)
d.thisdate = datetime.date (2013, 1, 1)
print (d.thisdate)
print (d.thisdate.format1)

Produces this output:

initing
getting
None
setting
getting
2013-01-01
getting
2013==01==01