On Wed, Apr 24, 2013 at 6:58 PM, Oscar Benjamin <oscar.j.benja...@gmail.com> wrote: > And here's another example: >>>> c = ([],) >>>> c > ([],) >>>> c[0] = c[0] + [1] > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: 'tuple' object does not support item assignment >>>> c > ([],) >>>> c[0] += [1] > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: 'tuple' object does not support item assignment >>>> c > ([1],)
The interpreter always uses a STORE operation after an in-place operation because it doesn't know if the target object was mutated in-place -- not with how it's currently implemented in ceval.c (in principle it could). This leads to half-completed operations that raise a TypeError like this when it tries to store the mutated object back to an immutable container. This can happen with any object that doesn't support assigning to subscripts or attributes, not just a tuple. _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
