Codingame ASCII Art Puzzle

ascii_art.py

l = int(raw_input())
h = int(raw_input())
t = raw_input()

result = []
characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ?"
for i in xrange(h):
    row = raw_input()
    threshold = len(row)/len(characters)
    chr_width = threshold 
    for c in t:
        c = c.upper()
        if c in characters:
            chr_index = characters.index(c)
        else:
            chr_index = len(characters) - 1
            
        chr_start = chr_index * chr_width
        chr_end =  (chr_index + 1) * chr_width
        result.append(row[chr_start:chr_end])
    result.append("\n")

print "".join(result)