Main.py

# coding: utf-8

import numpy.random as rd

def gen_typo(S):
    if len(S) <= 4:
        return S
    else:
        idx = [0]
        idx.extend(rd.choice(range(1, len(S)-1), len(S)-2, replace=False))
        idx.append(len(S)-1)
        result = []
        for i in range(len(S)):
            result.append(S[idx[i]])
        return ''.join(result)

s = "I couldn't believe that I could actually understand what I was reading : the phenomenal power of the human mind ."
s = s.split()
print(' '.join([gen_typo(i) for i in s]))