subtype custom 'float'. How to?

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Join Date: Jul 2008

Posts: 2

Reputation: mayapower is an unknown quantity at this point

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mayapower

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subtype custom 'float'. How to?

Jul 17th, 2008

Hi,

I am trying to create a cutom 'Float' type using built in 'float' type. Here is the code:

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
class Attribute(object):
    """
    Common attributes and methods for custom types
    """
 
    def __init__(self, name=None, type=None, range=None):
 
        self.__name = name
        self.__type = type
        self.__range = range
 
    #Read only attributes
    name = property(lambda self: self.__name)
    type = property(lambda self: self.__type)
    range = property(lambda self: self.__range)
 
 
class Float(float, Attribute):
    '''Custom Float type'''
    __slots__ = ('__name', '__type', '__range')
    def __init__(self, value=0.0, name=None, type=None, range=(0.0, 1.0)):
        try:
            super(Float, self).__init__(name=name, type=type, range=range)
            float.__init__(self, value)
        except:
            print 'Error : %s %s' % sys.exc_info()[:2]
 
a = Float(2.0, name='myFloat')
class Attribute(object):
    """
    Common attributes and methods for custom types
    """
       
    def __init__(self, name=None, type=None, range=None):
        
        self.__name = name
        self.__type = type
        self.__range = range
            
    #Read only attributes
    name = property(lambda self: self.__name)
    type = property(lambda self: self.__type)
    range = property(lambda self: self.__range)
    

class Float(float, Attribute):
    '''Custom Float type'''
    __slots__ = ('__name', '__type', '__range')
    def __init__(self, value=0.0, name=None, type=None, range=(0.0, 1.0)):
        try:
            super(Float, self).__init__(name=name, type=type, range=range)
            float.__init__(self, value)
        except:
            print 'Error : %s %s' % sys.exc_info()[:2]

a = Float(2.0, name='myFloat')

The problem is, I am not able to pass arguments when creating an instance. How do I solve this?

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Join Date: Jul 2006

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jrcagle

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Re: subtype custom 'float'. How to?

Jul 17th, 2008

I would probably take a completely different approach:

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 Python Syntax (Toggle Plain Text) 
class MyFloat(float):
 
    def __new__(self, name, value):
        return float.__new__(self, value)
 
    def __init__(self, name, value):
        self._name = name
 
    name = property(lambda self: self._name)
 
x=MyFloat("name", 1.5)
print x
print x._name
print x.name
class MyFloat(float):

    def __new__(self, name, value):
        return float.__new__(self, value)

    def __init__(self, name, value):
        self._name = name

    name = property(lambda self: self._name)
    
x=MyFloat("name", 1.5)
print x
print x._name
print x.name

The call to __new__ is necessary when subclassing immutable types like float -- the call order is __new__, followed by __init__ on initialization, and all of the arguments are passed to both.

Jeff