Rotate in place

rotate.py

def transpose_matrix(size, matrix):
    for y in range(size):
        for x in range(y):
            matrix[y][x], matrix[x][y] = matrix[x][y], matrix[y][x]
 
def flip_y_matrix(size, matrix):
    for y in range(size // 2):
        flip_y = size - y - 1
        for x in range(size):
            matrix[x][y], matrix[x][flip_y] = matrix[x][flip_y], matrix[x][y]

def rotate_matrix(size, matrix):
    transpose_matrix(size, matrix)
    flip_y_matrix(size, matrix)

def print_matrix(size, matrix):
    for y in range(size):
        for x in range(size):
            print(matrix[y][x], end="")
        print()

matrix = [list(row) for row in [
    "ABCD",
    "LMNE",
    "KP0F",
    "JIHG"
]]

rotate_matrix(4, matrix)
print_matrix(4, matrix)

rotate2.py

import itertools

def shift_refs(indices, get, set):
    prev_index = indices[-1]
    last_value = get(prev_index)
    iter = reversed(indices)
    next(iter)
    for index in iter:
        set(prev_index, get(index))
        prev_index = index
    set(indices[0], last_value)

def rotate_matrix(size, matrix):
    for y in range(size // 2):
        for x in range(y, size - y - 1):            
            def indices(x, y):
                while True:
                    yield x, y
                    y, x = x, size - 1 - y
                
            def get(coord):
                x, y = coord
                return matrix[y][x]
            def set(coord, v):
                x, y = coord
                matrix[y][x] = v
            shift_refs(list(itertools.islice(indices(x, y), 4)), get, set)

def print_matrix(size, matrix):
    for y in range(size):
        for x in range(size):
            print(matrix[y][x], end="")
        print()

matrix = [list(row) for row in [
    "ABCD",
    "LMNE",
    "KP0F",
    "JIHG"
]]

rotate_matrix(4, matrix)
print_matrix(4, matrix)