Arrays

# Manipulate list
A = list(range(10))
print(f'len() of A: {len(A)}')
A.append(5)
print(f'append() to A: {A}')
A.remove(5)
print(f'remove() first occurence from A: {A}')
A.insert(1, 999)
print(f'insert() first occurence from A: {A}')
print(f'min() of A: {min(A)}')
print(f'max() of A: {max(A)}')
del A[1]
print(f'del element with index i of A: {A}')
del A[:4]
print(f'del a range of elements of A: {A}')

# Assignment copy
colors = ['red', 'blue', 'green']
b = colors
b.append('white')
print(f'Copied/modified list: {b}')
print(f'Original list ALSO modified: {colors}')

# Shallow copy
a = [[1, 2], [2, 4]]
b = a[:] ## shallow copy
b.append([3, 6])
print(f'Copied/modified list: {b}')
print(f'Original list NOT modified: {a}')

# Shallow copy compound object => referenced to the original elements
a = [[1, 2], [2, 4]]
b = a[:] #shallow copy
b[0].append(3)
print(f'Copied/modified list: {b}')
print(f'Original list ALSO modified: {a}')
# List b has its own pointer, but its elements do not

# Deep copy, need copy module
import copy
a = [[1, 2], [2, 4]]
b = copy.deepcopy(a) ## deep copy
b[0].append(3) 
print(f'Copied/modified list: {b}')
print(f'Original list NOT modified: {a}')

# index where the element needs to be inserted in a sorted list 
import bisect
A = list(range(10))
print(A)
bisect.bisect(A, 6) # similar to bisect.bisect_right()

# if element exist, return index of the left of it
print(A)
bisect.bisect_left(A, 6) # similar to bisect.bisect_right()

# insert the element and not just the index
A = list(range(10))
print(A)
bisect.insort(A, 7) # same as bisect.insort_right()
print(A)

# reverse in-place
A = list(range(10))
A.reverse()
print(A)

# return an iterator
A = list(range(10))
for i in reversed(A): print(i, end=',')

# sort in-place
A = [4,3,2,1,0]
A.sort()
print(A)

# returns a copy
A = [4,3,2,1,0]
sorted(A)

# note the range is [0,5)
A = list(range(10))
A[0:5]

# from the back
A[-3:-1]

# skip n=2
A[0:5:2] 

# reverse with [::-1]
A[::-1] 

# rotate a list
A[5:] + A[:5]

[x**2 for x in range(6) if x%2==0]

# multiple levels
A = [1,2,3]
B = ['a', 'b']
[(x,y) for x in A for y in B]

# convert 2D to 1D
M = [['a', 'b', 'c'],['d', 'e']]
[x for row in M for x in row]

# 2 level looping
M = [[1,2,3], [4,5,6]]
[[x**2 for x in row] for row in M]

# remove the leading zeros
res = [0,0,1,2,3,4]
res[next((i for i,x in enumerate(res) if x!=0)):]

# what if they are all zeros
res = [0,0,0,0,0]
res[next((i for i,x in enumerate(res) if x!=0), len(res)):]

# Loop until something is found
mylist=[1,2,3]
for i in mylist:
    if i == 5:
        break
    print(i)
else:
    raise ValueError("List argument missing terminal flag.")

car = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}

x = car.get("price", 15000)

print(x)

# short circuits after second element
print (any([False, True, False, False]))  

# short circuits at the first element
print (all([False, True, True, False]))

def has_duplicates(block):
    return len(block) != len(set(block))
a=[1,2,3,1]
print(has_duplicates(a))

import timeit
block=[1,0,3,1,0]
time1=timeit.timeit(str(list(filter(lambda x: x != 0, block))), number=100000000)
print(time1)
time2=timeit.timeit(str([x for x in block if x != 0]), number=100000000)
print(time2)

# Example with 9x9 matrix and sub-block of 3x3
import math
M = [[0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 1, 2, 0, 0], [0, 0, 0, 0, 6, 0, 4, 0, 0], [0, 0, 0, 2, 0, 0, 0, 0, 5], [7, 0, 0, 0, 0, 0, 0, 0, 0], [0, 8, 3, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 3, 3, 0], [0, 0, 4, 0, 0, 0, 0, 0, 0]]
m = len(M)
n = int(math.sqrt(m))

# Original matrix
print('Original matrix:')
for i in range(m):
    for j in range(m):
        print(M[i][j], end=', ')
    print('')
print('---')
print('Sub-blocks of the matrix:')
for i in range(n):
    for j in range(n):
        for a in range(i*n, (i+1)*n):
            for b in range(j*n, (j+1)*n):
                print(M[a][b], end=',')
            print('')
        print('---')