Immutability and Python

[Mark Lawrence]

On 29/10/2012 15:20, andrea crotti wrote:
> I have a philosofical doubt about immutability, that arised while doing
> the SCALA functional programming course.
>
> Now suppose I have a simple NumWrapper class, that very stupidly does:
>
> class NumWrapper(object):
>      def __init__(self, number):
>          self.number = number
>
> and we want to change its state incrementing the number, normally I
> would do this
>
>      def increment(self):
>          self.number += 1
>
>
> But the immutability purists would instead suggest to do this:
>
>      def increment(self):
>          return NumWrapper(self.number + 1)
>
>
> Now on one hand I would love to use only immutable data in my code, but
> on the other hand I wonder if it makes so much sense in Python.
>
> My impression is that things get more clumsy in the immutable form, for
> example in the mutable form I would do simply this:
>
> number = NumWrapper(1)
> number.increment()
>
> while with immutability I have to do this instead:
> new_number = number.increment()
>
> But more importantly normally classes are way more complicated than my
> stupid example, so recreating a new object with the modified state might
> be quite complex.
>
> Any comments about this? What do you prefer and why?
>

I prefer practicality beats purity.

-- 
Cheers.

Mark Lawrence.