monetary applications (et al)

[Michael Stenner]

On Wed, Sep 18, 2002 at 05:35:32PM -0400, terry wrote:
> I do admit to being OO inhibited, so maybe you could take it from this 
> short piece code and execution results, and, provide a brief 
> description of what you would put into this money class that would 
> eliminate this error message, while maintaining the code simplicity.

While you're at it, please write me 4-liner that predicts the stock
market's behavior.  :)

Take a look at this:
http://python.org/doc/2.2.1/ref/numeric-types.html

for how to emulate numeric types.

					-Michael

> -------------------------------------------------
> class money:
> 	def __init__(self,name):
> 		self.name = name
> 
> unitprice = money(100)
> qty = 2
> amount = qty * unitprice
> 
> terry at terry:~> python money.py
> Traceback (most recent call last):
>   File "money.py", line 7, in ?
>     amount = qty * unitprice
> TypeError: unsupported operand type(s) for *: 'int' and 'instance'
> -------------------------------------------------
> 
> Support for mixed number types in expressions involving this money 
> class must come from somewhere - where?  And, it must be capable of 
> determing and setting amount to be of class money to be consistent with 
> the rest of Python's complexity hierarchy for the handling of numbers.
> 
> The rest of the problem is that the above is a trivial calculation.  
> What happens to your recommendation when faced with an additional 
> number type?
> 
> taxrate = 0.06
> amount = qty * unitprice + (qty*unitprice)*taxrate
> 
> As I see it, if Python had an intrinsic number type of 'money', the 
> logic for determing the results of the above calculation would be 
> easily determined and consistent with expectations, as in VB.
> 
> Thanks for your time,
> 
> terry
> 
> -- 
> http://mail.python.org/mailman/listinfo/python-list

-- 
  Michael Stenner                       Office Phone: 919-660-2513
  Duke University, Dept. of Physics       mstenner at phy.duke.edu
  Box 90305, Durham N.C. 27708-0305