习题:替换 abc 中的b 为1

s = "abc"

#1利用列表

s = list(s)

s[1]="1"
print("".join(s))

#2直接拼接

s = s[0] + "1" +s[2]

print(s)

#3 replace替换
s=s.replace("b","1")
print(s)

#4利用b分割再拼接

print("1".join(s.split("b")))

#5 正则sub替换
import re
print(re.sub(r"b","1",s))

#6删除再插入

s = list(s)

s.pop(1)
s.insert(1,"1")

print("".join(s))

习题1:删除一句英文中的所有英文标点。

s = "abd`1><>?"
import string

for v in s:
    if v in string.punctuation:
        s = s.replace(v,"")
print(s)

习题2、将"gloryroad"按照如下规则进行加密:字母对应的asscii码值进行加密,并且在码值前面加上码值长度,如g对应的码值为ord("g")=103,则字母g加密结果为3103 3是ascii的长度。
“gloryroad”正确输出加密结果为:"31033108311131143121311431112973100"

#encoding=utf-8
def encode_str(s):
    result = []
    for v in s:
        item = str(len(str(ord(v)))) + str(ord(v))
        result.append(item)
    return "".join(result)

s = "gloryroad"
print("%s 加密后: %s" %(s,encode_str(s)))

2、将上题中的加密字符串进行解密
方法1:
从头遍历每个字符串,当长度为3、2分别取到后面的ascii码,加入列表,最后把列表拼接成字符串

#encoding=utf-8
def decode_str(s):
    result = []
    index = 0
    length = len(s)
    while index < length:
        if s[index] == "3":
            #索引位置加上1后才是下一个要的长度值
            item = s[index + 1: index + 3 + 1]
            result.append(chr(int(item)))
            index += 4
        else:
            item = s[index + 1: index + 2 + 1]
            result.append(chr(int(item)))
            index += 3
    return "".join(result)

s = "31033108311131143121311431112973100"
print("%s 解密后: %s" %(s,decode_str(s)))

方法2:把上述方法合并成步骤

#encoding=utf-8
def decode_str(s):
    result = []
    index = 0
    length = len(s)
    while index < length:

        item = s[index + 1:index + int(s[index]) + 1]
        result.append(chr(int(item)))
        index += (int(s[index]) + 1)
    return "".join(result)

s = "31033108311131143121311431112973100"
print("%s 解密后: %s" %(s,decode_str(s)))

方法3:递归


#encoding=utf-8

def decode_str(s,result = []):
    if len(s) == 0:
        pass
    else:

        length = int(s[0])
        item = chr(int(s[1:length+ 1]))
        result.append(item)
        print(result)
        decode_str(s[length + 1:])

    return "".join(result)
s = "31033108311131143121311431112973100"
print("%s 解密后: %s" %(s,decode_str(s)))