[Tutor] Nested list anomaly

[dman]

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On Tue, Apr 30, 2002 at 10:07:32AM +1000, Hugh Stewart wrote:

| Test 1:
| >>> c1 =3D [[0]*2]*3
| >>> c1
| [[0, 0], [0, 0], [0, 0]]

This looks good, but what you have is a 3-element list where all
elements are identical references to the same 2-element list.  Since
lists are mutable, if you change the list, the change is seen by all
the references to it.

| Test 2:
| >>> c2 =3D [[0,0]]*3

Same situation.

| Test 3:
| >>> c3 =3D [[0,0],[0,0],[0,0]]

Here's what you wanted -- a 3-element list where each element is a
_separate_ list.


A shorter way of writing that (for longer lists) is :
    c =3D []
    for i in range(3) :
        c.append( [0]*2 )

    or

    c =3D [ [0]*2  for i in range(3) ]


-D

--=20

Come to me, all you who are weary and burdened, and I will give you
rest.  Take my yoke upon you and learn from me, for I am gentle and
humble in heart, and you will find rest for your souls.  For my yoke
is easy and my burden is light.
        Matthew 11:28-30
=20
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