Python Caesar

#-*-coding:utf-8-*-
import os
def encryption():
    str_raw = input("请输入明文：")
    k = int(input("请输入位移值："))
    str_change = str_raw.lower()
    str_list = list(str_change)
    str_list_encry = str_list
    i = 0
    while i < len(str_list):
        if ord(str_list[i]) < 123-k:
            str_list_encry[i] = chr(ord(str_list[i]) + k)
        else:
            str_list_encry[i] = chr(ord(str_list[i]) + k - 26)
        i = i+1
    print ("加密结果为："+"".join(str_list_encry))

def decryption():
    str_raw = input("请输入密文：")
    k = int(input("请输入位移值：(-1代表穷举)"))
    if k==-1:
        print("解密结果为：")
        for k in range(1,27):
            str_change = str_raw.lower()
            str_list = list(str_change)
            str_list_decry = str_list
            i = 0
            while i < len(str_list):
                if ord(str_list[i]) >= 97+k:
                    str_list_decry[i] = chr(ord(str_list[i]) - k)
                else:
                    str_list_decry[i] = chr(ord(str_list[i]) + 26 - k)
                i = i+1
            print ("".join(str_list_decry))
    else:
        print("解密结果为：")
        str_change = str_raw.lower()
        str_list = list(str_change)
        str_list_decry = str_list
        i = 0
        while i < len(str_list):
            if ord(str_list[i]) >= 97+k:
                str_list_decry[i] = chr(ord(str_list[i]) - k)
            else:
                str_list_decry[i] = chr(ord(str_list[i]) + 26 - k)
            i = i+1
        print ("".join(str_list_decry))

def caesar():
    print (u"1. 加密")
    print (u"2. 解密")
    choice = input("请选择：")
    if choice == "1":
        encryption()
    elif choice == "2":
        decryption()
    else:
        print (u"您的输入有误！")

if __name__ == '__main__':
    try:
        while True:
            caesar()
    except EOFError:
        exit()