[Python] some operations on list

When using a list in Python, we can see the indicator of the items as follows:
x = [0, 1, 2, 3, 4, 5, 6, 7, 8]
x[0],   x[1],   x[2],   x[3],   x[4],   x[5],   x[6],   x[7],   x[8]
x[-0],  x[-8], x[-7],  x[-6],  x[-5], x[-4],  x[-3],  x[-2], x[-1]   <= reverse direction
x[-9]
some usages of list in Python are shown below:

	>>> x = [0,1,2,3,4,5,6,7,8]
	>>> x[1:5]
	[1, 2, 3, 4] #print items from x[1] to x[4] (excluding x[5])
	>>> x[1:]
	[1, 2, 3, 4, 5, 6, 7, 8] #print the items start from x[1] to the end
	>>> x[:5]
	[0, 1, 2, 3, 4] #print the first 5 items
	>>> x[1::3]
	[1, 4, 7] #print items..x[1 + 0*3], x[1 + 1*3], x[1 + 2*3] ....
	>>> x[-1]
	8 #print the last item in x
	>>> x[:-1]
	[0, 1, 2, 3, 4, 5, 6, 7] #print items start from the head, x[0], to the one before x[-1] (excluding x[-1])
	#note that if you want to copy a list x to a new list y, using y = x doesn't perform the copy task, it is a reference
	#example of reference operation
	>>> x = [1, 2, 3, 4, 5]
	>>> y = x
	>>> y[1] = 7
	>>> x
	[1, 7, 3, 4, 5]
	#example of copy operation
	>>> y = x[:]
	>>> y[0] = 7
	>>> x
	[1, 7, 3, 4, 5] #not affected by the operation on y

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