[Tutor] Immutable objects

[Alan Gauld]

"Nitin Das" <nitin.162 at gmail.com> wrote 

> class mymut(object):
> 
>  def __setattr__(self,k,v):
>      if hasattr(self,k):
>          if self.__dict__.get(k) == None:
>              self.__dict__[k] = v

Do you need to look up the dict? 
Surely you could just use

if self.k is None
   self.k = v

which looks a lot simpler to me...

>          else:
>              raise TypeError("Cant Modify Attribute Value")

You could mention the class for example.
Compare it with the string and tuple messages:

>>> 'fred'[2] = 'g'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment

>>> (1,2,30)[1] = 5
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>>

So if your error said 
TypeError: mymut object does not support item assignment

that would be more consistent with the Python internal objects.

>      else:
>          raise TypeError("Immutable Object")

The Python immutables seem to raise an Attribute Error here 
rather than a Type error. And again mentioning the class name 
makes debugging easier:

>>> 'l'.x = 4
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'str' object has no attribute 'x'
>>>

HTH,

-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/