tpc at cryptic.com wrote:
> hey guys, I've been experimenting with Python's datetime module, and I
> created a function that, given a person's birthdate, calculates how
> old that person is. Now I want to create a class called
> age_calculator that does much the same thing. My class inherits from
> the date class, but I have to type 'from datetime import date' before
> I can initialize the class definition. Is there some way to avoid
> this ?
No.
In order to use class inheritance syntax,
class some_class(some_object):
some_object must be defined.
Otherwise you'll get a variable not defined error.
You could make your own class called 'date' and inherit from that,
but what would be the point of that?
>
> Also, once I type the import statement and initialize my class
> definition, I can create an instance of age_calculator. The instance
> of age_calculator stores the given birthdate, and gives me a infinite
> loop traceback when I call self.today(). If I don't inherit from
> date, I would need to put the import statement somewhere inside a
> method, and I don't recall ever seeing that done.
What makes you think you'd have to import within a method?
Import datetime.date into the global namespace.
That's perfectly alright.
Especially since your class depends on it being available.
> Part of me feels like that's not as elegant as defining an
> age_calculator class that inherits from datetime.date, but I'm not
> sure how to do this. For what it's worth, here's my pseudocode (that
> inherits from date module) and working code (that does not inherit
> from date module):
The way you'd go about doing this is to make an extra function that is
unique to your inherited class (for example, calculate_age).
>
> from datetime import date
>
> class age_calculator(date):
> def __init__(self, year, month, day):
> time_delta = self.today() - self
> number_of_years = time_delta.days / 365
> return number_of_years
This init method is overriding the init of the inherited date class.
The reason today() doesn't work is probably because of this.
>
> class age_calculator:
> def __init__(self, year, month, day):
> self.year = year
> self.month = month
> self.day = day
>
> def calculate_age(self):
> from datetime import date
> birth_date = date( self.year, self.month, self.day)
> date_today = date.today()
> time_delta = date_today - birth_date
> number_of_years = time_delta.days / 365
> return number_of_years
>
Just move the import outside of the class.
from datetime import date
class age_calculator:
def __init__(self, year, month, day):
self.year = year
self.month = month
self.day = day
def calculate_age(self):
birth_date = date( self.year, self.month, self.day)
date_today = date.today()
time_delta = date_today - birth_date
number_of_years = time_delta.days / 365
return number_of_years
I don't think you really want to inherit from date.
HTH,
-Luke