Nested Lists, Copying & List Programs

marks = [[78, 85, 90],      # student 1: Eng, Maths, CS
         [66, 72, 81],      # student 2
         [90, 95, 99]]      # student 3
print(marks[1])             # whole row of student 2
print(marks[1][2])          # student 2, CS
print(marks[2][0], len(marks), len(marks[0]))

marks = [[78, 85, 90], [66, 72, 81], [90, 95, 99]]
for row in marks:
    for m in row:
        print(m, end='\t')
    print('| total =', sum(row))

a = [1, 2, 3]
alias = a                 # same list, two names
copy1 = a[:]              # slicing makes a copy
copy2 = list(a)           # list() makes a copy
copy3 = a.copy()          # copy() method
a.append(4)
print('a     :', a)
print('alias :', alias)
print('copies:', copy1, copy2, copy3)
print(alias is a, copy1 is a)

def increase(prices, percent):
    for i in range(len(prices)):
        prices[i] = round(prices[i] * (1 + percent / 100), 2)

def new_list(prices):
    prices = [0, 0]           # re-assigns the LOCAL name only
    return prices

p = [100, 250, 80]
increase(p, 10)
print(p)
print(new_list(p), p)

nums = [34, 7, 89, 21, 56, 7]
key = int(input('Search for: '))
found = False
for i in range(len(nums)):
    if nums[i] == key:
        print(key, 'found at index', i)
        found = True
        break
if not found:
    print(key, 'not found')

data = [4, 2, 4, 9, 2, 4, 7]
seen = []
for x in data:
    if x not in seen:
        seen.append(x)
        print(x, 'occurs', data.count(x), 'time(s)')
print('Without duplicates:', seen)

nums = [45, 89, 23, 89, 67, 12]
first = second = float('-inf')
for x in nums:
    if x > first:
        second = first
        first = x
    elif first > x > second:
        second = x
print('Largest:', first, '| Second largest:', second)

L = [1, 2, 3, 4, 5, 6]
half = len(L) // 2
print('Swap halves :', L[half:] + L[:half])
print('Rotate left :', L[1:] + L[:1])
print('Rotate right:', L[-1:] + L[:-1])
for i in range(0, len(L) - 1, 2):       # swap neighbours
    L[i], L[i + 1] = L[i + 1], L[i]
print('Swap pairs  :', L)

A = [[1, 2], [3, 4]]
B = [[5, 6], [7, 8]]
S = [[A[i][j] + B[i][j] for j in range(2)] for i in range(2)]
T = [[A[j][i] for j in range(2)] for i in range(2)]      # transpose
print('A + B =', S)
print('Transpose of A =', T)

items = []
while True:
    print('1-Add 2-Delete 3-Show 4-Exit')
    ch = input('Choice: ')
    if ch == '1':
        items.append(input('Item: '))
    elif ch == '2':
        it = input('Item to delete: ')
        if it in items:
            items.remove(it)
        else:
            print('Not in list')
    elif ch == '3':
        print('List:', items)
    elif ch == '4':
        break