Rotate a block of text from a file

gistfile1.txt

# rotate text in a file, such as banner text
# surprised this isn't a library function, for silly text operations

import sys
import re

def create_matrix(height):
    matr = list()
    for i in range(0, height):
        matr.append(list())
    return matr

with open(sys.argv[1], 'r') as reader:
    MATRIX = None
    for line in reader:
        line = re.sub('\n', ' ', line)
        if not MATRIX:
            HEIGHT = len(line)
            MATRIX = create_matrix(len(line))
            rev_ind = list(reversed(range(0, HEIGHT)))
        for idx, car in enumerate(line):
            MATRIX[rev_ind[idx]].append(car)
        if len(line) < HEIGHT:
            for idx in range(len(line), HEIGHT):
                MATRIX[rev_ind[idx]].append(' ')

    for x in MATRIX:
        print ("".join(x))