Explanation of how nested list comprehension works?

Question

I have no problem for understanding this:

a = [1,2,3,4]
b = [x for x in a]

I thought that was all, but then I found this snippet:

Answer 1

Here is how I best remember it: (pseudocode, but has this type of pattern)

[(x,y,z) (loop 1) (loop 2) (loop 3)]

where the right most loop (loop 3) is the inner most loop.

[(x,y,z)    for x in range(3)    for y in range(3)    for z in range(3)]

has the structure as:

for x in range(3):
    for y in range(3):
        for z in range(3):
            print((x,y,z))

Edit I wanted to add another pattern:

[(result) (loop 1) (loop 2) (loop 3) (condition)]

Ex:

[(x,y,z)    for x in range(3)    for y in range(3)    for z in range(3)    if x == y == z]

Has this type of structure:

for x in range(3):
    for y in range(3):
        for z in range(3):
            if x == y == z:
                print((x,y,z))