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Python3 数据类型-字符串

时间:2019-07-09 23:55:50      阅读:168      评论:0      收藏:0      [点我收藏+]

字符串是 Python 中最常用的数据类型,是一个个字符组成的有序的序列,是字符的集合。

一 字符串定义

创建字符串很简单,可以使用引号(‘或"或""")来创建字符串,只要为变量分配一个值即可。

实例(Pytho3.0+):

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s1 = ‘string‘
s2 = "string2"
s3 = ‘‘‘this‘s a "String"‘‘‘
s4 = ‘hello \n magedu.com‘
print(s4)
#hello
# magedu.com
 
s5 = r‘hello \n magedu.com‘
print(s5)
#hello \n magedu.com
#字符串前面加r,表示的意思是禁止字符转义
 
s6 = ‘c:\windows\nt‘
print(s6)
#c:\windows
#t
 
s7 = R"c:\windows\nt"
# 字符串前面加r,表示的意思是禁止字符转义
print(s7)
#c:\windows\nt
 
s8 = ‘c:\windows\\nt‘
print(s7)
#c:\windows\nt
# \ 转义字符,去除特殊字符的含义
 
sql = """select * from user where name=‘tom‘"""

二 字符串元素访问

索引访问 

实例(Python3.0+):

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sql = "select * from user where name=‘tom‘"
print(sql[4])
# 字符串‘c‘
 
sql[4] = ‘o‘
# TypeError: ‘str‘ object does not support item assignment
# 错误的,因为字符串是不可变类型

序列访问

实例(Python3.0+):

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str1 = "python"
for c in str1:
    print(c)
    print(type(c)) # 什么类型,当然还是字符串类型(str)
 
"""
p
<class ‘str‘>
y
<class ‘str‘>
t
<class ‘str‘>
h
<class ‘str‘>
o
<class ‘str‘>
n
<class ‘str‘>
"""

迭代访问

实例(Python3.0+):

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str1 = "python"
str1 = list(str1)
print(str1)
# [‘p‘, ‘y‘, ‘t‘, ‘h‘, ‘o‘, ‘n‘]

三 字符串修改 

str.replace(old.new[,count]) -> str

  1. 字符串中找到配皮替换为新字符串,返回新字符串
  2. count表示替换几次,不指定就是全部替换 

实例(Python3.0+):

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str1 = ‘www.baidu.com‘
print(str1.replace(‘www‘, ‘sss‘))
# ‘sss.baidu.com‘
print(str1.replace(‘w‘, ‘s‘, 2))
# ‘ssw.baidu.com‘ 

str.strip([chars]) -> str

  1. 从字符串两端去除指定的字符集chars中的所有字符
  2. 如果chars没有指定,去除两端的空白字符及换行符

实例(Python3.0+):

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s = "\r \n\t hello python \n \t"
print(s.strip())
#"hello python"
s = "i am very very very sorry"
print(s.strip(‘iy‘))
#" am very very very sorr"

str.lstrip([chars]) -> str

  1. 从左开始去除指定的字符集chars中的所有字符
  2. 如果chars没有指定,去除左边的空白字符及换行符

实例(Python3.0+):

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s = "i am very very very sorry"
print(s.lstrip(‘iy‘))
#" am very very very sorry"

str.rstrip([chars]) -> str

  1. 从右开始去除指定的字符集chars中的所有字符
  2. 如果chars没有指定,去除右边的空白字符及换行符

实例(Python3.0+):

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s = "i am very very very sorry"
print(s.rstrip(‘iy‘))
#"i am very very very sorr"

四 字符串查找

str.find(sub,[,start[,end]]) -> int 

  1. 在指定的区间(start,end),从左到右,查找子串sub,找到返回索引,没找到返回-1

实例(Python3.0+):

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s = "i am very very very sorry"
print(s.find(‘very‘))  # 5
print(s.find(‘very‘, 5))   # 从索引5开始查找  # 5
print(s.find(‘very‘, 6, 13))  # 从索引6到13间查找 # -1

str.rfind(sub,[,start[,end]]) -> int 

  1. 在指定的区间(start,end),从右到左,查找子串sub,找到返回索引,没找到返回-1

实例(Python3.0+):

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s = "i am very very very sorry"
print(s.rfind(‘very‘, 10))
print(s.rfind(‘very‘, 10, 15))
print(s.rfind(‘very‘, -10, -1))  # 15
print(s.rfind(‘very‘, -1, -10) ) # -1

str.index(sub[,start[,end]]) -> int  

  1. 在指定的区间(start,end),从左到右,查找子串sub,找到返回索引,没找到抛出异常ValueError
  2. 一般情况下查找字符串不适用index,返回异常不容易处理,会导致程序崩溃

实例(Python3.0+):

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s = "i am very very very sorry"
 
print(s.index(‘very‘)) # 5 索引从0开始
print(s.index(‘very‘,5) )
print(s.index(‘very‘,6,13))

str.rindex(sub[,start[,end]]) -> int

  1. 在指定的区间(start,end),从右到左,查找子串sub,找到返回索引,没找到抛出异常ValueError
  2. 一般情况下查找字符串不适用index,返回异常不容易处理,会导致程序崩溃

实例(Python3.0+):

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s = "i am very very very sorry"
 
print(s.rindex(‘very‘, 10))
print(s.rindex(‘very‘, 10, 15))
print(s.rindex(‘very‘, -10, -1))  # 15
print(s.rindex(‘very‘, -1, -10))  # -1

str.count(sub[,start[,end]]) -> int

  1. 在指定的区间(start,end),从左到右,统计子串sub出现的次数

实例(Python3.0+):

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s = ‘I am very very very sorry‘
 
print(s.count(‘very‘)) # 3
print(s.count(‘very‘,5))  # 3
print(s.count(‘very‘,5,14))  # 2

五 字符串判断

str.endswith(suffix[,start[,end]]) -> bool

  1. 在指定区间(start,end),字符串是否是suffix结尾

str.startswith(suffix[,start[,end]]) -> bool

  1. 在指定区间(start,end),字符串是否是suffix开头

实例(Python3.0+):

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s = "i am very very very sorry"
 
"""
首先打印出每个字符的索引:
方法1:
num = 0
for i in s:
    print(num,"-",i,end="")
    num +=1
# 0 - i 1 -   2 - a 3 - m 4 -   5 - v 6 - e 7 - r 8 - y 9 -   10 - v 11 - e 12 - r 13 - y 14 -   15 - v 16 - e 17 - r 18 - y 19 -   20 - s 21 - o 22 - r 23 - r 24 - y
 
方法2:
for i,j in enumerate(s):
    print(i,"-",j,end=" ")
# 0 - i 1 -   2 - a 3 - m 4 -   5 - v 6 - e 7 - r 8 - y 9 -   10 - v 11 - e 12 - r 13 - y 14 -   15 - v 16 - e 17 - r 18 - y 19 -   20 - s 21 - o 22 - r 23 - r 24 - y
"""
print(s.startswith(‘very‘))
# False
print(s.startswith(‘very‘, 5))
# True
print(s.startswith(‘very‘, 5, 9))
# True
print(s.endswith(‘very‘, 5, -1))
# False
print(s.endswith(‘very‘, 5, 100))
# True

is系列

技术分享图片

六 字符串切割

str.split(sep=None,maxsplit=-1) -> list of 

  • 从左到右
  • seq指定分割字符串,缺省的情况下空白字符串(一个或多个空白字符)作为分隔符
  • maxsplit指定分割的次数,-1表示遍历整个字符串(默认是-1) 

实例(Python3.0+):

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s1 = "i‘m \ta super student"
 
print(s1.split())
# ["i‘m", ‘a‘, ‘super‘, ‘student‘]
# \t 在默认的情况下被当成分隔符(\t表示Tab键)
 
print(s1.split(‘ ‘))
# ["i‘m", ‘\ta‘, ‘super‘, ‘student‘]
 
print(s1.split(‘ ‘, maxsplit=2))
# ["i‘m", ‘\ta‘, ‘super student‘]
 
print(s1.split(‘\t‘, maxsplit=2))
# ["i‘m ", ‘a super student‘]  

str.rsplit(sep=None,maxsplit=-1) -> list of strings

  • 从右往左切割
  • sep指定分割字符串,缺省的情况下空白字符串作为分隔符
  • maxsplit指定分割次数,-1表示遍历整个字符串(默认是-1)

实例(Python3.0+):

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s1 = "i‘m \ta super student"
 
print(s1.rsplit())
# ["i‘m", ‘a‘, ‘super‘, ‘student‘]
# \t 在默认的情况下被当成分隔符
 
print(s1.rsplit(‘super‘))
# ["i‘m \ta ", ‘uper ‘, ‘tudent‘]
 
print(s1.rsplit(‘ ‘))
# ["i‘m", ‘\ta‘, ‘super‘, ‘student‘]
 
print(s1.rsplit(‘ ‘, maxsplit=2)) #或 print(s1.rsplit(‘ ‘, 2))
# ["i‘m", ‘\ta‘, ‘super student‘] maxsplit可以省却,直接写值
 
print(s1.rsplit(‘\t‘, maxsplit=2))
# ["i‘m ", ‘a super student‘]

str.splitlins([keepnds]) -> list of strings

  • 按照行来切割字符串
  • keepends指的是是否保留行分割符,默认不保留分隔符
  • 行分割符包括\n \r\n \r等

实例(Python3.0+):

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str1 = ‘ab c\n\nde fg\rkl\r\n‘
 
print(str1.splitlines())
#[‘ab c‘, ‘‘, ‘de fg‘, ‘kl‘]
print(str1.splitlines(True))
#[‘ab c\n‘, ‘\n‘, ‘de fg\r‘, ‘kl\r\n‘]
 
s1 = """i‘m a super student.
you‘re a super teacher."""
 
print(s1)
#i‘m a super student.
#you‘re a super teacher.
 
print(s1.splitlines())
#["i‘m a super student.", "you‘re a super teacher."]
 
print(s1.splitlines(True))
#["i‘m a super student.\n", "you‘re a super teacher."]

str.partition(sep) -> (head,sep,tail)

  • 从左至右,遇到分隔符就把字符串分割成两部分,返回头、分隔符、尾三部分的三元组;如果没有找到分隔符,就返回头、2个空元素的三元组
  • sep 分隔字符串,必须指定

实例(Python3.0+):

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s1 = "i‘m a super student"
 
print(s1.partition(‘s‘))
# ("i‘m a","s","uper student")
 
print(s1.partition(‘ ‘))
#("i‘m", ‘ ‘, ‘a super student‘)
 
print(s1.partition(‘abc‘))
# ("i‘m a super student",‘‘,‘‘)

str.rpartition(sep) -> (head,sep,tail)

  • 从右到左,遇到分隔符就把字符串分割成两部分,返回头、分隔符、尾三部分的三元组;如果没有找到分隔符,就返回头、2个空元素的三元组
  • sep 分隔字符串,必须指定

实例(Python3.0+):

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str1 = "I am supper student"
 
print(str1.rpartition(" "))
# (‘I am supper‘, ‘ ‘, ‘student‘)

七 字符串大小写

str.upper()

  • 把字符串中的字符转换成大写

实例(Python3.0+):

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str1 = "i am a supper student"
print(str1.upper())
# I AM A SUPPER STUDENT

str.lower()

  • 把字符串中的字符转换成小写
  • 只能转换26个英文字母,特殊字符无法转换

实例(Python3.0+):

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str1 = "I AM A SUPPER STUDENT"
print(str1.lower())
# i am a supper student

str.casefold()

  • 把字符串中的字符转换成小写
  • 比之lower,可以转换特殊字符

实例(Python3.0+):

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S1 = "Runoob EXAMPLE....WOW!!!"  # 英文
S2 = "ß"  # 德语
 
print(S1.lower())
# runoob example....wow!!!
print(S1.casefold())
# runoob example....wow!!!
print(S2.lower())
# ß
print(S2.casefold())  # 德语的"ß"正确的小写是"ss"
# ss

str.swapcase()

  • 把字符串中的大写转换成小写,小写字符转换成大写

实例(Python3.0+):

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str1 = "I Am A Supper Student"
print(str1.swapcase())
#i aM a sUPPER sTUDENT

八 字符串排版

str.title() -> str

  1. 标题的每个单词首字母大写

str.capitalize() -> str

  1. 首个字母大写

实例(Python3.0+):

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str1 = "i am supper student"
 
print(str1.title())
#I Am Supper Student
print(str1.capitalize())
#I am supper student

center(width[,fillchar]) -> str

  1. width 打印宽度
  2. fillchar 填充的字符

实例(Python3.0+):

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s1 = ‘abc‘
print(s1.center(50,‘#‘))
#‘#######################abc########################‘

zfill(width) -> str

  1. width 打印宽度,居右,左边用0填充

实例(Python3.0+):

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s1 = ‘abc‘
print(s1.zfill(50))
‘00000000000000000000000000000000000000000000000abc‘

ljust(width[,fillchar]) -> str

  1. width 打印宽度,左对齐,右边默认空格填充
  2. fillchar 填充字符

实例(Python3.0+):

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s1 = "abc"
print(s1.ljust(20))
#"abc                 "
print(s1.ljust(20,"*"))
#abc*****************

rjust(width[,fillchar]) -> str

  1. width 打印宽度,右对齐,左边默认空格填充
  2. fillchar 填充字符

实例(Python3.0+):

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s1 = ‘abc‘
print(s1.rjust(20))
#"                 abc"
print(s1.rjust(50,"$"))
#‘$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$abc‘

Python3 数据类型-字符串

原文:https://www.cnblogs.com/Jintaonet/p/11161105.html

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