python基础之字符串篇
字符串是 Python 中最常用的数据类型。我们可以使用单引号或者双引号来创建字符串。
例如：
str_example = "demo" str_example = 'demo'
字符串常用的方法
1. find() 方法 语法： str.find(substr) 例子： str_example = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you , you can't do it.If you want something, go get it. " #查找dream在str_example第一次出现的位置 position = str_example.find('dream') # 10 #可以指定位置查询 position = str_example.find('you',10) # 17 position = str_example.find('you',20,100) # 92 #可以指定位置查询,如果查询不到，则返回-1
position = str_example.find('you',20,50) # -1
2. rfind() 方法 和find() 方法用法一样，只不过是从右向左查找
语法： str.rfind(substr)
例子：
#查找dream在mystr从右向左指定区域内第一次出现的位置
mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. "
flag = mystr.rfind('you',20,120) #115
3. index() 方法 ,在字符串中查找子字符串出现的位置 语法 str.index(substr)
例子： #查找第一次出现的位置,如果没有则会跑出ValueError异常 mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.index('you') # 115 mystr.index('she') # ValueError: substring not found 所以避免异常发生 try: mystr.index('she') except Exception as e: print(-1)
4. rindex()方法 和index()方法用法一致，只不过是在右侧向左侧查找 语法： str.rindex(substr) 例子： mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.rindex('you') #115 mystr.rindex('she') # ValueError: substring not found #查找从右到左第一次出现的位置,如果没有则会跑出ValueError异常 try: mystr.rindex('she') except Exception as e: print(-1
5. count() 方法 查询子字符串出现的次数 语法：str.count(substr) 例子：
#查找在mystr中you出现的次数 mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.count('you') # 4
6. len() 方法 计算字符串的长度 语法：len(str) 例子： #计算 mystr 的长度 mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " len(mystr)# 146
7. replace()方法，字符串替换 语法 str.replace('new_str','old_str') 例子： # 将mystr中的 you 替换成 你 mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.replace('you','你')# You got a dream, 你 gotta protect it. People can't do something themselves,they wanna tell 你 你 can't do it.If 你 want something, go get it.
# 指定修改个数
mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. "
mystr.replace('you','你',2) # You got a dream, 你 gotta protect it. People can't do something themselves,they wanna tell 你 you can't do it.If you want something, go get it
8. split()方法 字符串分割方法 语法： str.split(substr) 例子： #以空格 分隔字符串 获取一个list列表 mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.split(' ') # ['You', 'got', 'a', 'dream,', 'you', 'gotta', 'protect', 'it.', 'People', "can't", 'do', 'something', 'themselves,they', 'wanna', 'tell', 'you', 'you', "can't", 'do', 'it.If', 'you', 'want', 'something,', 'go', 'get', 'it.', '']
9. capitalize() 方法 首字母大写 语法： str.capitalize() 例子： mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.capitalize() #You got a dream, you gotta protect it. people can't do something themselves,they wanna tell you you can't do it.if you want something, go get it.
10. titile() 方法，字符串标题化，也就是说字符串每个单词的首字母大写，其余为小写 语法： str.title() 例子： mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.tyitle() # You Got A Dream, You Gotta Protect It. People Can'T Do Something Themselves,They Wanna Tell You You Can'T Do It.If You Want Something, Go Get It.
11. istitle()方法 判断 字符串每个单词的首字母是否大写,其余为小写，返回boolean值 语法: str.istitle() 例子： mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.istitle() #Flase mystr1 = 'Hello World' mystr1.istitle() # True
12. startswith() 判断字符串是否以某子字符串开头，返回boolean值 语法： str.startswith(substr) 例子： mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.startswith('Y') # True mystr.startswith('x') #Flase
13. endswith() 判断字符串是否以某子字符串结尾，返回boolean值 语法：str.endswith(substr) 例子： mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.endswith(' ') # True mystr.endswith('.') # Flas
14. lower() 方法 字符串所有字符转化成小写字母 语法： str.lower() 例子： mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.lower() # you got a dream, you gotta protect it. people can't do something themselves,they wanna tell you you can't do it.if you want something, go get it.
15. upper() 方法 字符串所有字符转换成大写字母 语法：str.upper() 例子： mystr = "You got a dream, you gotta protect it. People can't do something themselves,they wanna tell you you can't do it.If you want something, go get it. " mystr.upper() # YOU GOT A DREAM, YOU GOTTA PROTECT IT. PEOPLE CAN'T DO SOMETHING THEMSELVES,THEY WANNA TELL YOU YOU CAN'T DO IT.IF YOU WANT SOMETHING, GO GET IT.
16. ljust() 方法 返回一个原字符串左对齐,并使用空格填充至指定长度的新字符串。如果指定的长度小于原字符串的长度则返回原字符串。 语法： str.ljust(width,fillchar) 例子： mystr = "You got a dream" mystr.ljust(50,'*') # You got a dream***********************************
17. rjust()方法 返回一个字符串右对齐，并使用空格或指定字符填充新的字符串，如果指定的长度小于原字符串，则返回原字符串 语法： str.rjust(width,fiilchar) 例子： mystr = 'You got a dream' mystr.rjust(50,'*') # ***********************************You got a dream
18. center() 方法 返回一个原字符串居中,并使用空格填充至长度 width 的新字符串。默认填充字符为空格。 语法： str.center(width,fillchar) 例子： mystr = "You got a dream" mystr.center(50,'*') # *****************You got a dream******************
19. lstrip()方法 去除左边的空格、换行符或者指定字符 语法： str.lstrip() 例子： mystr = ' You got a dream' mystr.lstrip() #You got a dream mystr.lstrip(' Y') #ou got a dream
20. rstrip()方法 去除右边的空格、换行符或者指定字符 语法： str.rstrip() 例子： mystr = ' You got a dream ' mystr.rstrip() # You got a dream mystr.lstrip(' m') # You got a drea
21. strip()方法 去除两侧的空格、换行符或者指定字符 语法： str.strip() 例子： mystr = ' You got a dream ' mystr.strip() #You got a dream
22. partition() 方法 用来根据指定的分隔符将字符串进行分割,返回一个元组 语法：str.partition(substr) 例子： mystr = 'You got a dream' mystr.partition('a') # (' You got ', 'a', ' dream')
23. rpartition()方法 从右向左找指定字符分割成元祖 语法： str.rpartition(substr) 例子： mystr = 'You got a dream' mystr.rpartition('a') # (' You got a dre', 'a', 'm')
24. splitlines()方法 按照行('\r', '\r\n', \n')分隔，返回一个包含各行作为元素的列表，如果参数 flag为 False，不包含换行符，如果为 True，则保留换行符。 语法：str.splitlines(flag) 例子： mystr = 'You got a\n dream' mystr.splitlines() # [' You got a', ' dream'] mystr.splitlines(True) # [' You got a\n', ' dream']
25. isalnum()方法 判断字符串是否只由数字和字母组成,返回boolean值 语法：str.isalnum() 例子： mystr = 'Yougot3dreams' mystr.isalnum() # True mystr1 = 'You got 3 dreams !' mystr1.isalnum() # False
26. isdigit() 方法 判断字符串是否只有数字 返回boolean值 语法： str.isdigit() 例子： mystr = '0123456789' mystr.isdigit() # True mystr1 = '0123456789!' mystr1.isdigit() # Flase
27. isalpha() 方法 判断字符串是否只有字母组成，返回boolean值 语法：str.isalpha() 例子： mystr = 'Yougotadream' mystr.isalpha() #True mystr1 = 'You got a dream' mystr1.isalpha() # Flase
28. isspace()方法 判断字符串是否只由空格组成，返回boolean值 语法： str.isspace() 例子： mystr = ' ' mystr.isspace() #True mystr1 = 'You got a dream' mystr1.isspace() # False
29. join() 方法 用于将序列中的元素以指定的字符连接生成一个新的字符串。 语法： str.join(str) 例子： mystr1 = ' ' mystr2 = 'hello' mystr1.join(mystr2) # h e l l o
