I am sure there is a reason for this design in Python but why is it so difficult to clone a list? Copying a variable is easy

foo = 1
bar = foo
bar = 2
print bar # returns 2
print foo # returns 1

But trying to do the same thing, which is what makes sense in my mind coming from other languages, does not work. You have to add the list splice otherwise it doesn't work.

Then I spent a day trying to figure out how to copy a 2d list and that was even more frustrating. I had the following code and none of these worked to properly copy a list without modifying the original.

foo = [[1,2], [3,4], [5,6]]
bar = foo # doesnt work
bar = foo[:] # doesnt work
bar = list(foo) # doesnt work
bar = list(foo[:]) # doesnt work
bar = []
bar += foo # doesnt work
bar = []
bar.append(foo) # doesnt work
for i, x in enumerate(foo):
    bar[i] = x[:]
# didnt work

I am sure I tried a few more methods and none of them worked. It was finally this method that was the only way I could find to copy a 2d list, modify the new one without affecting the original list

bar = [x[:] for x in foo]

So why is copying a list in python just so hard?

I have the following matrix:

matrix =     [
        [ 9, 0, 0, 0, 8, 0, 3, 0, 0 ],         
        [ 2, 0, 0, 2, 5, 0, 7, 0, 0 ],         
        [ 0, 2, 0, 3, 0, 0, 0, 0, 4 ],
     ] 

Say that I want to make "new_matrix" have a 3x3 block matrix which is copied from "matrix". In this case, I want new_matrix to have:

new_matrix =     [         
        [8 ,0 ,3 ],         
        [5, 0, 7 ],         
        [0, 0, 0 ],     
    ] 

Essentially, what I want is to tell my program to copy the values from the row index [0:0+2] and from the columns [4:4+2]. I tried using a for-loop to go through the requested indexes and adding those values into new_matrix:

new_matrix = [             
        [0, 0, 0 ],             
        [0, 0, 0 ],             
        [0, 0, 0 ],         
    ]  
for i in range(len(matrix[0:0+2])):         
    for j in range(len(matrix[i][4:4+2])):             
        new_matrix = matrix[i][j] 

This doesn't seem to work. What am I doing wrong?