Help, replacing the actual value from a data strucutre in a iterator

Andrew McGregor andrew at indranet.co.nz
Sat Jan 4 13:15:35 CET 2003


Hi,

--On Saturday, January 04, 2003 03:31:06 -0800 george hart 
<gehart24 at yahoo.com> wrote:

>> o is now bound to 0
>>
>> > o=100   # where i want this assignment to change a[0] to 100
>>
>> No way.  You are simply rebinding 'o' to a new value.  Just write
>> 'a[0] = 100'!
>
> Hi,
>
> I'm sorry, I think my example was not very good.  I can't just write
> 'a[0]' because the *real* data structure I am working with is very
> complex and nested.  It would be more like a[1][10][20][40] etc..
>
> I am a relatively new to python so I am probably trying solve the
> problem the way I would in C (it would be nice to have pointers right
> now :-).   The returned value from the .next() method appears to be
> pointing to the same memory address as the respective element in the
> data structure.  It seems logical that there should be an easy way to
> modify it.

It is pointing to the same address; but it's the address of the integer 
value 0, not the list slot containing that 0.

> Plus, there must be a way to do this?  What is the point of being able
> use a generator to iterate over a structure if you can't modify any of
> the values?

How about:

from __future__ import generators
from types import *

a=[0,1,2,[20,30,40],9,3]
def generator(l):
    for i in xrange(len(l)):
        if type(l[i]) is list:
            for q in generator(l[i]):
                yield q
        else:
            yield (lambda : l.__getitem__(i),
                   lambda x: l.__setitem__(i, x))

print a
gen = generator(a)
g, s = gen.next()
print g()
s(100)
print a
g, s = gen.next()
g, s = gen.next()
g, s = gen.next()
g, s = gen.next()
s(100)
print a

which prints:
[0, 1, 2, [20, 30, 40], 9, 3]
0
[100, 1, 2, [20, 30, 40], 9, 3]
[100, 1, 2, [20, 100, 40], 9, 3]




>
>
> Thanks,
>
> George
> --
> http://mail.python.org/mailman/listinfo/python-list
>
>







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