Hi, all,

A couple of questions regarding mutabilty:

First, I noticed a comment at the beginning of quadratic_forms/binary_qf.py 
from Stein:  "make immutable".  Can anyone (William?) elaborate on what that 
means?  They don't currently (e.g., sage-4.6.1-a3) seem to be very immutable:
sage: q1=BinaryQF((-2,0,1))
sage: q1._a=3
sage: q1
 3*x^2 + y^2

Second, on this note, is there anywhere written a discussion of what 
immutability means in Python?  A quick check of the doc (for Python 2.[67]) 
doesn't seem to lead anywhere.  For example, can one declare a "class" 
immutable and have it stick, or is there extra work involved to ride herd on 
all "instance variables" that one would want to be unchangeable directly?

Hope that question is clear.  Thanks for any comments.

Justin


--
Justin C. Walker, Curmudgeon at Large
Institute for the Absorption of Federal Funds
--
Democracy is two wolves and a lamb
   voting on what to have for lunch.
Liberty is a well-armed lamb contesting
   the vote.



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