# File: Programs/ChapterLists/listCompare.py
""" Mutable sequences
L[i] = x 	item i of s is replaced by x   
L.copy() 	creates a shallow copy of s (same as L[:]) (5) 
L.pop([i]) ----retrieves the item at i and also removes it from s (2) 
L.remove(x) ---remove the first item from s where L[i] == x (3) 
s + t --- the concatenation of s and t (6)(7) 
s * n or n * s --- n shallow copies of s concatenated (2)(7) 
>>> r = range(0, 20, 2) # range(startInt,endInt,step)
>>> list(range(10)) -> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> L=[['a','b'],[1,2]] and >>> L[0][1] -> 'b'
>>> Ls = [[]] * 3 -> >>> Ls is [[], [], []]
>>> L = [[] for i in range(2)] #makes [[],[]]
>>> L[0].append(3)
>>> L[1].append(5)
>>> L -> [[3], [5], [7]]
"A shallow copy constructs a new compound object and then (to the extent possible) 
inserts references into it to the objects found in the original.
"A deep copy constructs a new compound object and then, recursively, 
inserts copies into it of the objects found in the original."
"""
L = [1, 2, 3]
M = L #whatever happens to L happens to M
N = L.copy() # N is a new list  has same initial value as L
L.pop() # modify just L but M gets also modifyed!! L = [1,2]
print("original list L= ", L, "M = ", M, "N with copy keeps original!")
x = 5
L.append(x) # L1 = [1,2,5] modifies L !
# N is the same