Unit4字符串以及正则表达式

常用方法1

<code>s1 = "HelloWorld"

new_s1 = s1.lower()

print(s1, new_s1)

s2 = new_s1.upper()

print(new_s1,s2)

#字符串的分割

e_mail = "zhl@qq.com"

lst = e_mail.split("@")

print("邮箱名：", lst[0],"邮箱服务器域名：",lst[1])

#统计出行次数

print(s1.count("l"))

#检索操作

print(s1.find("o"))#首次出现位置

print(s1.find("p"))#-1没有找到

print(s1.index("o"))

#print(s1.index("p"))#ValueError: substring not found

#判断前缀和后缀

print(s1.startswith("h"))

print(s1.startswith("H"))

print("demo.py".endswith(".py"))#True

print("text.txt".endswith(".txt"))#Ture

常用方法2

<code>s = "helloworld"

#替换

'''

def replace(self,

__old: str,

__new: str,

__count: SupportsIndex = ...) -> str

'''

new_s = s.replace("o","你好",1)#最后一个参数是替换次数，默认是全部替换

print(s,new_s)

'''

字符串在指定的宽度范围内居中

def center(self,

__width: SupportsIndex,

__fillchar: str = ...) -> str

'''

print(s.center(20))

print(s.center(20, "-"))

'''

去掉字符串左右的空格

def strip(self, __chars: str | None = ...) -> str

'''

s = " hello world "

print(s.strip())

print(s.lstrip())

print(s.rstrip())

#去掉指定的字符 与顺序无关

s3 = "dl_Helloworld"

print(s3.strip("ld"))

print(s3.lstrip("ld"))

print(s3.rstrip("ld"))

格式化

<code>name = "马冬梅"

age = 18

score = 98.4

print("name：%s,age:%d,score:%.1f"%(name,age,score))

#f-string

print(f"name:{name},age:{age},score{score}")

#format()

print("name:{0},age{1},score{2}".format(name,age,score))

详细格式

<code>s = "helloworld"

print("{0:*<20}".format(s))

print("{0:*>20}".format(s))

print("{0:*^20}".format(s))

#居中对齐

print(s.center(20,"*"))

#千位分隔符（只适用于整数和读点书

print("{0:,}".format(123456789))

print("{0:,}".format(123456789.312313))

print("{0:.2f}".format(123456789.312313))

print("{0:.5}".format(s))

#整数类型

a = 425

print(

"2进制：{0:b},8进制：{0:o},10进制：{0:d},16进制：{0:X},".format(a)

)

#科学计数法

pi = 3.1415926

print("{0:.2f},{0:.2E},{0:.2e},{0:.2%}".format(pi))

字符串的编码和解码

<code>

s = "伟大的人民"

#编码 str -> bytes

#默认UTF-8

scode = s.encode(errors="replace")code>

print(scode)

'''

def encode(self,

encoding: str = ...,

errors: str = ...) -> bytes

'''

scode_gbk= s.encode("gbk",errors="replace") #gbk中中文占两个字节code>

print(scode_gbk)

#编码中的出错问题

s2 = "✌ye耶"

#errors = strickt(default) or replace or ignore or xmlcharrefreplace

scode_error = s2.encode("gbk",errors='replace')code>

print(scode_error)

# 解码过程 bytes -》 str

print(bytes.decode(scode_gbk, "gbk"))

print(bytes.decode(scode, "utf-8"))

print(s2)

数据的验证

#阿拉伯数据判定

print("12345".isdigit())#True

print("一二三".isdigit())#False

print("0x123".isdigit())#False

print("Ⅰ".isdigit())#False

print("一1".isdigit())#False

print("="*20)

#所有字符都是数字

'''

def isnumeric(self) -> bool

Return True if the string is a numeric string, False otherwise.

A string is numeric if all characters in the string are numeric and there is at

least one character in the string.

'''

print("123".isnumeric())#True

print("一二三".isnumeric())#True

print("0b100".isnumeric())#Fakse

print("ⅠⅡⅢ".isnumeric())#True

print("壹贰叁".isnumeric())#True

print("="*20)

#所有字母都是字母（包含中文字符）

'''

def isalpha(self) -> bool

Return True if the string is an alphabetic string, False otherwise.

'''

print("hello你好".isalpha())#True

print("hello你好123".isalpha())#False

print("hello你好一二三".isalpha())#True

print("hello你好0b100".isalpha())#False

print("hello你好ⅠⅡⅢ".isalpha())#False

print("hello你好壹贰叁".isalpha())#True\

print("="*20)

#判断字符的大小写 判断是读取全部字母

print("hello你好".islower())

print("hellO你好".islower())

print("Hello你好".islower())

print("hello=".islower())

print("Hello=".isupper())

print("="*20)code>

# isspace

print(" ".isspace())

print("hello ".isspace())

print(" hello ".isspace())

字符串拼接

s1 = "hello"

s2 = "world"

#(1)

print(s1 + s2)

#join()

print("-".join([s1,s2]))

#直接拼接

print("hello""world")

#format

print("%s%s" % (s1,s2))

print(f"{s1}{s2}")

print("{0}{1}".format(s1,s2))

去重

s = "hello world"

new_s = ""

for item in s:

if item not in new_s:

new_s += item

print(new_s)

#使用索引

new_s2 = ""

for i in range(len(s)):

if s[i] not in new_s2:

new_s2 += s[i]

print(new_s2)

print(new_s2 == new_s)

print(id(new_s2))

print(id(new_s))

#通过集合

new_s3 = set(s)

print(new_s3)

lst = list(new_s3)

print(lst)

lst.sort(key=s.index)

print(lst)

print("".join(lst))

正则表达式

<code>import re #导入

pattern = '\d\.\d+' #限定符+ \d 0-9数字出现一次或多次

s = "I study Python3 every day"

match = re.match(pattern, s, re.I)

print(match) #None

s2 = "3.11Python I study every day"

match1 = re.match(pattern, s2)

print(match1)#<re.Match object; span=(0, 4), match='3.11'>code>

print("匹配值的起始位置：",match1.start())

print("匹配值的结束位置：",match1.end())

print("匹配值的区间的位置：",match1.span())

print("待匹配值的字符串：",match1.string)

print("匹配的数据：",match1.group())

'''

匹配值的起始位置： 0

匹配值的结束位置： 4

匹配值的区间的位置： (0, 4)

待匹配值的字符串： 3.11Python I study every day

匹配的数据： 3.11`

'''

#search

pattern = "\d\.\d+"

s = "I study python3.11 every day python2.7 i used"

match = re.search(pattern, s)

print(match)

s1 = "2.71I study python3.11 every day python i used"

match1 = re.search(pattern, s1)

print(match1)

#findall

lst = re.findall(pattern,s)

lst1 = re.findall(pattern,s1)

print(lst)

print(lst1)

#sub and split

import re

#sub()

pattern = "黑客|破解|反爬"

s = "我需要学习python，想当黑客，破解一些VIP视频，python可以实现无底线反爬吗"

'''

def sub(pattern, repl, string, count=0, flags=0):

"""Return the string obtained by replacing the leftmost

non-overlapping occurrences of the pattern in string by the

replacement repl. repl can be either a string or a callable;

if a string, backslash escapes in it are processed. If it is

a callable, it's passed the Match object and must return

a replacement string to be used."""

return _compile(pattern, flags).sub(repl, string, count)

'''

new_s = re.sub(pattern, "XXX", s)

print(new_s)

#split

s1 = "https://cn.bing.com/search?q=zhl&cvid=016dc0451cab427eaa8d8f04787fae17"

pattern1 = "[?|&]"

lst = re.split(pattern1,s1)

print(lst)

练习

Exer1

'''

判断车牌归属地

使用列表存储N个车牌号码，通过遍历列表以及字符串的切片操作判断车牌的归属地

'''

lst = ["湘A0001","京A0001","沪A0001","粤A0001"]

for item in lst:

area = item[0:1]

print(item, "归属地为：",area)

Exer2

'''

统计字符串中出现指定字符的次数

内容为 ”HelloPython，HelloJava，HelloC++“

用户从键盘录入要查询的字符，不区分大小写

要求统计出要查找的字符串出现的次数

'''

s1 = "HelloPython，HelloJava，HelloC++"

word = input("输入要统计的字符：")

print(f"{word}在{s1}一共出现了{s1.upper().count(word.upper())}")

Exer3

'''

格式化输出商品的名称和价格

使用列表存储一些商品数据，使用循环遍历输出商品的信息，要求对商品的编号进行格式化为6位

单价保存2位小鼠，并在前面添加人名币符号输出

'''

lst = [

["01","PC","MS",5000],

["02","car","BYD",50000],

["03","mp","NS",5],

["04","TV","TCL",500],

]

print("编号\t\t\t名称\t\t\t品牌\t\t\t单价")

for item in lst:

for i in item:

print(i,end="\t\t\t")code>

print()

#格式化操作

for item in lst:

item[0] = "0000" + item[0]

item[3] = "￥{0:.2f}".format(item[3])

print("编号\t\t\t\t名称\t\t\t\t品牌\t\t\t\t单价")

for item in lst:

for i in item:

print(i,end="\t\t\t")code>

print()

Exer4

'''

提取文本中所有图片的链接地址

'''

import random

import string

# 定义基础URL

base_url = "https://example.com/image"

# 定义可能的查询参数

params = {

"resolution": ["1080p", "720p", "4k"],

"format": ["jpg", "png", "gif"],

"quality": ["high", "medium", "low"],

"random": lambda: ''.join(random.choices(string.ascii_letters + string.digits, k=6))

}

# 生成随机查询参数

def generate_query_params():

query_params = []

for key, values in params.items():

if callable(values):

value = values()

else:

value = random.choice(values)

query_params.append(f"{key}={value}")

return "&".join(query_params)

# 生成完整的图片URL

def generate_complex_image_url():

query_string = generate_query_params()

return f"{base_url}?{query_string}"

# 生成并打印10个复杂的图片URL

for _ in range(10):

print(generate_complex_image_url())

import re

# 编译正则表达式模式

pattern = re.compile(r"\d+")

# 使用编译后的正则表达式对象进行匹配

text = "There are 123 apples and 456 oranges."

match = pattern.search(text)

if match:

print("Found:", match.group())

test_s = '"https://example.com/image?resolution=1080p&format=jpg&quality=high&random=abcdef","https://example.com/image?resolution=4k&format=jpg&quality=medium&random=saxkir","asd",sad,"asd",d"""""https://example.com/image?resolution=4k&format=jpg&quality=medium&random=driv3X",https://example.com/image?resolution=1080p&format=png&quality=low&random=xG7jqi'

# 使用捕获组

regex_pattern_with_groups = r'(https://example\.com/image\?resolution=(1080p|720p|4k)&format=(jpg|png|gif)&quality=(high|medium|low)&random=([a-zA-Z0-9]{6}))'

# 不使用捕获组

regex_pattern_without_groups = r'https://example\.com/image\?resolution=[0-9a-z]+&format=[0-9a-z]+&quality=[0-9a-z]+&random=[0-9a-zA-Z]{6}'

# 使用findall查找所有匹配的URL

lst_with_groups = re.findall(regex_pattern_with_groups, test_s)

lst_without_groups = re.findall(regex_pattern_without_groups, test_s)

# 打印所有匹配的URL

print("With groups:")

for item in lst_with_groups:

print(item) # item是一个元组

print("\nWithout groups:")

for item in lst_without_groups:

print(item) # item是整个匹配的字符串