使用 Join 为啥会莫名奇妙的输出空格？

正在做 pythonchallenge,Q2,我自己用的是字典的方法

words ="g fmnc wms bgblr rpylqjyrc gr zw fylb. rfyrq ufyr amknsrcpq ypc dmp. bmgle gr gl zw fylb gq glcddgagclr ylb rfyr'q ufw rfgq rcvr gq qm jmle. sqgle qrpgle.kyicrpylq() gq pcamkkclbcb. lmu ynnjw ml rfc spj. "

secret = {"a":"c","b":"d","c":"e","d":"f","e":"g","f":"h ","g":"i","h ":"j","i":"k","j":"l","k":"m","l":"n","m":"o","n":"p","o":"q","p":"r","q":"s","r":"t","s":"u","t":"v","u":"w","v":"x","w":"y","x":"z","y":"a","z":"b"}

answer=[]
i=0
while i < len(words):
    j = words[i]
    if j in secret.keys():
        answer.append(secret[j])
    else:
        answer.append(j)
    i = i +1
print(answer)
print("".join(answer))

测试发现 最后的 answer 这个 list 是没有问题的， 内容是

['i', ' ', 'h ', 'o', 'p', 'e', ' ', 'y', 'o', 'u', ' ', 'd', 'i', 'd', 'n', 't', ' ', 't', 'r', 'a', 'n', 's', 'l', 'a', 't', 'e', ' ', 'i', 't', ' ', 'b', 'y', ' ', 'h ', 'a', 'n', 'd', '.', ' ', 't', 'h ', 'a', 't', 's', ' ', 'w', 'h ', 'a', 't', ' ', 'c', 'o', 'm', 'p', 'u', 't', 'e', 'r', 's', ' ', 'a', 'r', 'e', ' ', 'f', 'o', 'r', '.', ' ', 'd', 'o', 'i', 'n', 'g', ' ', 'i', 't', ' ', 'i', 'n', ' ', 'b', 'y', ' ', 'h ', 'a', 'n', 'd', ' ', 'i', 's', ' ', 'i', 'n', 'e', 'f', 'f', 'i', 'c', 'i', 'e', 'n', 't', ' ', 'a', 'n', 'd', ' ', 't', 'h ', 'a', 't', "'", 's', ' ', 'w', 'h ', 'y', ' ', 't', 'h ', 'i', 's', ' ', 't', 'e', 'x', 't', ' ', 'i', 's', ' ', 's', 'o', ' ', 'l', 'o', 'n', 'g', '.', ' ', 'u', 's', 'i', 'n', 'g', ' ', 's', 't', 'r', 'i', 'n', 'g', '.', 'm', 'a', 'k', 'e', 't', 'r', 'a', 'n', 's', '(', ')', ' ', 'i', 's', ' ', 'r', 'e', 'c', 'o', 'm', 'm', 'e', 'n', 'd', 'e', 'd', '.', ' ', 'n', 'o', 'w', ' ', 'a', 'p', 'p', 'l', 'y', ' ', 'o', 'n', ' ', 't', 'h ', 'e', ' ', 'u', 'r', 'l', '.', ' ']

但是最后使用 join 将 list 转变成 str 时，结果就变成了

i h ope you didnt translate it by h and. th ats wh at computers are for. doing it in by h and is inefficient and th at's wh y th is text is so long. using string.maketrans() is recommended. now apply on th e url. 

注意其中莫名奇妙的多了几个空格，正常应该是

i hope you didnt translate it by hand. thats what computers are for. doing it in by hand is inefficient and that's why this text is so long. using string.maketrans() is recommended. now apply on the url. 

请教下大家这莫名奇妙的空格是怎么被输出的？