functions, list, default parameters

Terry Reedy tjreedy at udel.edu
Tue Nov 2 18:16:27 CET 2010


On 11/2/2010 3:12 AM, Lawrence D'Oliveiro wrote:

>> "Immutable objects" are just those without an obvious API for modifying
>> them.

After initial creation ;-)/

> They are ones with NO legal language constructs for modifying them.

Suppose I write an nasty C extension that mutates tuples. What then 
would be illegal about

import tuple_mutator
t = (1,2)
tuple_mutator.inc(t)
t
# (2,3)

 > Hint: if
> a selector of some part of such an object were to occur on the LHS of an
> assignment, and that would raise an error, then the object is immutable.

I am not sure what you are saying here, and how it applies to

 >>> lt = [(0,)]
 >>> lt[0][0] = 1
Traceback (most recent call last):
   File "<pyshell#1>", line 1, in <module>
     lt[0][0] = 1
TypeError: 'tuple' object does not support item assignment
 >>> tl = ([0],)
 >>> tl[0][0] = 1
 >>> tl
([1],)


-- 
Terry Jan Reedy




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