Main.py

# coding: utf-8

import random

def gen_typo(S):
    return ' '.join(
        s 
        # 長さ4以下の単語はそのまま返す
        if len(s) <= 4 
        # 長さ5以上の単語は1文字目と2文字目を残してシャッフル
        else s[0] + ''.join(random.sample(s[1:-1], k=len(s)-2)) + s[-1] 
        for s in S.split()
        )

S = "I couldn't believe that I could actually understand what I was reading : the phenomenal power of the human mind ."
print(gen_typo(S))