Re: [Tutor] Clash of the Titans and Mundane Matters

[John Fouhy]

Michael Powe wrote:
Here's an example:  in Java, I wrote an
application to track my travelling expenses (I'm a consultant; this
tracking of expenses is the itch I am constantly scratching.  ;-)
I've also written this application in a perl/CGI web application as
well.)  It's easy to see the outline of this task:  create an abstract
class for expense and then extend it for the particular types of
expenses -- travel, food, transportation, lodging and so forth.  In
python, I guess I'd create a class and then "subclass" it.  But
... what are reading/writing to files and printing?  
I'm not sure exactly what output you're after ... But what about 
something like this?

class Expense(object):
    def __init__(self, amount):
        self.amount = amount
class Travel(Expense):
    def __str__(self):
        return 'Travel: $%.2f' % float(self.amount)
class Food(Expense):
    def __str__(self):
        return 'Food: $%.2f' % float(self.amount)
class Accommodation(Expense):
    def __str__(self):
        return 'Accommodation: $%.2f' % float(self.amount)
myExpenses = [Travel(2300), Accommodation(200), Food(12.50),
              Food(19.95), Food(2.35), Travel(500)]
for e in myExpenses:
    print e
out = file('myExpenses.txt', 'w')
for e in myExpenses:
    out.write(str(e) + '\n')
out.close()
---------------------------------------------------------------------
This produces output:
Travel: $2300.00
Accommodation: $200.00
Food: $12.50
Food: $19.95
Food: $2.35
Travel: $500.00
and the same in the file 'myExpenses.txt'.
The str() function automatically calls .__str__() on its argument (if 
you don't define __str__, it will call a boring default one).  And the 
print command automatically calls str() on its arguments.

--
John.
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