Message: 6
Date: Mon, 12 Jun 2006 05:59:16 -0400
From: Kent Johnson [EMAIL PROTECTED]
Subject: Re: [Tutor] assignment statements in python
Actually sorting doesn't require copying the values in the list, it just
requires moving values to different locations of the list.
*
Yes. I wish to know how I can , for examplem,
given
B = [1,2,4,5],
move B[3] to a position of newly created B[4],
move B[2] to position of B[3]
Assign value 3 to position B[2].
That is, I wish to insert the value 3, into it's sorted place within the
already sorted list B.
A list element is somewhat like a name - it is a reference to a value,
not a container for a value.
If you say
a=[1,2,3]
B=a
then a and B refer to the same list. Likewise, if you say
x=[ [1,2,3], [4,5,6] ]
x[1] = x[0]
then x[1] and x[0] refer to the same list.
***
x = [ [1,2,3],[4,5,6]]
x
[[1, 2, 3], [4, 5, 6]]
x[1] = x[0]
x
[[1, 2, 3], [1, 2, 3]]
Needed to make sure I understood what would happen.
Does the value [4,5,6] get erased at this point?
If you want x[1] (or B) to
refer to a new list, you have to copy the old list:
x[1] = x[0][:]
list[:] is the slice of the list that goes from the beginning to the end
- a copy.
*
I missed the significance of the [:] slice until you explained it.
So, now I could write my code as
# to insert 3 between 2 and 4 in
B = [1,2,4,5]
B.append(B[3:3])
# I expected B[4] to have the value 5 at this point.
# It is empty. Why?
# So, I compensate by making the next line
B[4] = B[3:3]
# B[4] is still an empty list. Why?
# I try
B[4] = B[3]
# That seemed to work.
B[3] = B[2]
# Now I try
B[2] = 3
That worked.
However, I don't see the difference between this code,
and what I had before that did not work.
Kermit[EMAIL PROTECTED]
Kent
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