python receiving error using ord function "TypeError: ord() expected a character, but string of length 2 found"

I have modified some Python code found, which calculates the transition matrix for an observed sequence (transitions named here).

For some reason it works fine, but when I put a number above or equal to "10" I get this error:

"ord() expected a character, but string of length 2 found"

states_no = 10
transitions = [['10', '1', '1', '2', '3', '1']]
trans_matr = []

for k in range(len(transitions)):


    def rank(c):
        return ord(c) - ord('1')

    T = [rank(c) for c in transitions[k]]
    #print(transitions[k])
    #create matrix of zeros

    M = [[0]*states_no for _ in range(states_no)]

    for (i,j) in zip(T,T[1:]):
        M[i][j] += 1

    #now convert to probabilities:
    for row in M:
        n = sum(row)
        if n > 0:
            row[:] = [f/sum(row) for f in row]

    #print M:
    trans_matr.append(M)
    #for row in M:
        #print(row)
#print(trans_matr)

trans_matr_array=numpy.array(trans_matr)
print(trans_matr_array)

I guess it has something to do with the character recognition. Is there any way to put numbers up to 14 without getting this error?

As far as I can tell the code only uses ord() for calculating the difference between the input and 1. Does your input include non-numeric characters? If not, simply change the function "rank":

def rank(c)
    return int(c) - 1

I assume you only need integers, you can change it to float to accept any number.

If you need to also accept non-numeric characters:

def rank(c):
    if c.isnumeric():
        return int(c) - 1
    elif len(c) == 1:
        return ord(c) - ord('1')
    else:
        raise TypeError('non numeric inputs should have length 1')