Perl and Python

Welcome to Dream.In.Code
	Become an Expert! Join 300,455 Programmers for FREE! Get instant access to thousands of experts, tutorials, code snippets, and more! There are 1,595 people online right now. Registration is fast and FREE... Join Now! Chat LIVE With a Expert

Inheritance problem...

Inheritance problem..., Why is my custom class not functioning?

Options

code_m

21 Jun, 2009 - 01:58 PM

Post #1

D.I.C Head

Joined: 21 Apr, 2009
Posts: 118

Thanked: 8 times
My Contributions

( Python, 3.0 )

I have defined a class called Money_value in which I want to inherit the float class, but whenever I do something that is not defined by the new class, the variable becomes float ?

python


class Money_value(float):
    def __str__(self):
        """Return a "beautified" string, to look more like a standard 2-decimal money value
        """
        value_list = super().__str__().split(".")
        if len(value_list[1]) == 1:
            return "$" + value_list[0] + "." + value_list[1] + "0"
        else:
            cent_list = [x for x in value_list[1]]

            # round the second decimal if needed
            if len(cent_list) > 2 and int(cent_list[2]) >= 5:
                cent_list[1] = str(int(cent_list[1]) + 1)

            return "$" + value_list[0] + "." + "".join(cent_list[:2])

so lets say I want to do this:

python


>>> value = Money_value(83.45)
>>> value += 2.30
>>> type(value)
<class 'Money_value'>

I get this:

python


>>> value = Money_value(83.45)
>>> value += 2.30
>>> type(value)
<class 'float'>

I can even do:

python


>>> value = Money_value(83.45)
>>> value += Money_value(2.30)
>>> type(value)
<class 'float'>

I'm so confused as to why any variable continues to silently becomes float?

This Post Was Helpful!

Register for Free to Make These Ads Go Away!

crazyjugglerdrummer	RE: Inheritance Problem... 21 Jun, 2009 - 02:03 PM Post #2
YOUR AD HERE Joined: 7 Jan, 2009 Posts: 677 Thanked: 94 times Dream Kudos: 425 My Contributions	interesting, possibly they're gettting downcast to float since the += is an operator taking a float, unless you extended and implemented it yourself. I haven't heard much about people extending number classes, as normally you want a hasa relationship instead of isa, but do whatever you like . ;D
	This Post Was Helpful!

code_m	RE: Inheritance Problem... 22 Jun, 2009 - 06:29 PM Post #3
D.I.C Head Joined: 21 Apr, 2009 Posts: 118 Thanked: 8 times My Contributions	I suppose it would be easier to just use a simple function for the str conversion, but I was going for a fully object-oriented approach, and making such a change without inheritance would be outside of this realm. Oh well.
	This Post Was Helpful!