modifying values of List or Dictionary when iterating on them

[aspineux]

Hello

I just want to update the data inside List or Dictionary without
adding or deleting object.

is this correct ?

l=[1, 2, 3]
for i, v in enumerate(l):
    l[i]=v+1

d=dict(a=1, b=2, c=3)
for k, v in d.iteritems():
    d[k]=d[k]+1

Both works, but :

are they correct ?
are they optimum for big structure ?

Thanks