[Tutor] attribute overwrite

[Prasad, Ramit]

>class DateTime(datetime.datetime):
>  def __init__(self, year, month, day, *args):
>    super().__init__()
>    if self.year >= 1000:
>      self.year = self.year % 1000

I have no idea how you could use the sample you have given (or why) but, this was actually a fun exercise that forced me to learn more about immutable types (which makes sense because a date should never really be modifiable if you think about it). Instead of overriding the __init__ you need to override the __new__ method. Try the following

>>> class DateTime(datetime.datetime):
...     def __new__(self, year, month, day, *args):
...         if year >= 1000:
...             year = year % 1000
...         return super( DateTime, self ).__new__(self, year, month, day, *args )
...     
>>> DateTime( 2011, 1, 1 )
DateTime(11, 1, 1, 0, 0)

Ramit


Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology
712 Main Street | Houston, TX 77002
work phone: 713 - 216 - 5423

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From: tutor-bounces+ramit.prasad=jpmorgan.com at python.org [mailto:tutor-bounces+ramit.prasad=jpmorgan.com at python.org] On Behalf Of rail shafigulin
Sent: Friday, December 09, 2011 4:15 PM
To: tutor at python.org
Subject: Re: [Tutor] attribute overwrite


On Fri, Dec 9, 2011 at 4:43 PM, rail shafigulin <rail.shafigulin at gmail.com> wrote:
i need to overwrite and attribute from the inherited class. i also need to run the constructor of the super class. here is the code

import datetime

class DateTime(datetime.datetime):
  def __init__(self, year, month, day, *args):
    super().__init__(year, month, day, *args)
    if self.year >= 1000:
      self.year = self.year % 1000

i'm getting the following error:
AttributeError: attribute 'year' of datetime.datetime objects are not writable.

some of you might suggest to change

self.year = self.year % 1000
to
self.yr = self.year % 1000

but i'd need to keep the name the same.

any help is appreciated.
my apologies, but there is a minor mistake in the code:

import datetime

class DateTime(datetime.datetime):
  def __init__(self, year, month, day, *args):
    super().__init__()
    if self.year >= 1000:
      self.year = self.year % 1000

def main():
  mytme = DateTime.now()

if __name__ == '__main__'
  main()
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