rot90 O(1) space

rot90_o1.py

import numpy as np

arr = np.arange(1, 26).reshape((5, 5))
arr2 = np.arange(1, 26).reshape((5, 5))

def rot90(arr):

    for circle in range(len(arr) // 2):

        for item in range(0, len(arr) - 1 - 2 * circle):

            sidey = len(arr) - 1 - circle

            arr[circle][circle + item],     \
            arr[circle + item][sidey],      \
            arr[sidey][sidey - item],       \
            arr[sidey - item][circle] =     \
            arr[sidey - item][circle],      \
            arr[circle][circle + item],     \
            arr[circle + item][sidey],      \
            arr[sidey][sidey - item]

    return arr

assert (np.rot90(arr, -1) == rot90(arr2)).all()