How to define a class within a function using exec()

Question

I have a lengthy, repetitive code full of classes where they each do almost the same thing, and I was trying to do something like this to shorten it:

def newClass(cName, para):
 string = '''class '''+cName+'''(str):
 def __new__(cls, num): 
 return(str.__new__(cls, func('''+para+''')))'''
 exec(string)

but the new class is neither a part of newClass or defined on its own, how can I make it so it creates the new class as if it were not defined in a function? If that's impossible, how can I make it so that I can do something like:

newClass('Fun', 'p')
newClass.Fun('inp')

---

Edit: I am making a base conversion program, and wanted to be able to do things that python does not do like bin(a) + bin(b). Here is a simplified version of one of my classes:

class Bin(str):
 '''Binary (base 2) number'''
 def __new__(cls, num): 
 return(str.__new__(cls, baseconv(num, 2, '01')))
 def __int__(self): 
 return(intconv(self, 2, '01'))
 def __add__(a, b): 
 return(Bin(a.__int__() + b.__int__()))
 def __sub__(a, b): 
 return(Bin(a.__int__() - b.__int__()))
 ...
class Ter(str):
 '''Ternary (base 3) number'''
 def __new__(cls, num): 
 return(str.__new__(cls, baseconv(num, 3, '012')))
 def __int__(self): 
 return(intconv(self, 3, '012'))
 def __add__(a, b): 
 return(Ter(a.__int__() + b.__int__()))
 def __sub__(a, b): 
 return(Ter(a.__int__() - b.__int__()))
 ...

Where baseconv and intconv are two functions I've defined previously.

• user1114: Consider whether constructing a class using the type function may work instead in your case. Using exec/eval is strongly discouraged, and is rarely a suitable design. (Generating classes in general is slightly frowned-upon, but if it's neccessary then using type may be reasonable.)
• mgilson: @JaredGoguen -- eval won't work here. It only works on expressions and class definition is definitely not an expression.
• mgilson: @diligar -- Can you show us a simplified example of some "repetitive code full of classes" that you would like to refactor? That may help us to give better suggestions (e.g. using type as suggested by Jeremy).
• user2357112: Why do you have so many classes that do almost the same thing? It sounds like you might be overusing inheritance.
• diligar: @JaredGoguen I tried that, but I figured exec would be a better idea after looking at this question