Python学习日记(一) String函数使用
s = "abcaDa a" s2 = "123a abc ABCSAa s " s3 = " as b123" s4 = ' &abc123 c ## '
1.str.capitalize()
将原字符串内的首字母转成大写,其他部分小写,再返回新字符串
print("s.capitalize() = {function}".format(function = s.capitalize()))
Output：
s.capitalize() = Abcada a
2.str.upper()
将原字符串的字母转为大写
print("s.upper() = {function}".format(function = s.upper()))
Output:
s.upper() = ABCADA A
3.str.lower()
将原字符串的字母转为小写
print("s.lower() = {function}".format(function = s.lower()))
Output:
s.lower() = abcada a
4.str.swapcase()
将原字符串内的大写小写反转
print("s.swapcase() = {function}".format(function = s.swapcase()))
Output:
s.swapcase() = ABCAdA A
5.str.title()
原字符串内如果有特殊字符(包括数字)连接字母,则将特殊字符后的首个英文字母转化为大写形态,并返回新字符串
print("s2.title() = {function}".format(function = s2.title()))
Output:
s2.title() = 123A Abc Abcsaa S
6.str.center()
str.center(宽度,填充字符) 将字符串以居中的格式返回,若宽度值比len(s)小则返回原字符串,填充以从左到右为规则,填充字符的默认值为空格,值可以自己更改
print("s2.center() = {function}".format(function = s2.center(19,'&'))) print("s2.center() = {function}".format(function = s2.center(20,'&')))
Output:
#s2 = 123a abc ABCSAa s s2.center() = &123a abc ABCSAa s s2.center() = &123a abc ABCSAa s &
7.str.expandtabs()
str.expandtabs(tabsize = 8) 将原字符串中 以前的字符补满8位(默认),tabsize的值从0-7即8位,在0-7中任意取值则默认tabsize = 8,此后
往上+1，就相当于增加一个空格
print("s3.expandtabs ={function}".format(function = s3.expandtabs())) print("s3.expandtabs ={function}".format(function = s3.expandtabs(0))) print("s3.expandtabs ={function}".format(function = s3.expandtabs(5))) print("s3.expandtabs ={function}".format(function = s3.expandtabs(8))) print("s3.expandtabs ={function}".format(function = s3.expandtabs(9)))
Output:
#s3 = " as b123" s3.expandtabs = as b123 s3.expandtabs =as b123 s3.expandtabs = as b123 s3.expandtabs = as b123 s3.expandtabs = as b123
8.String_len = len(str)
公共方法,计算字符串的长度
print("s2_length = {0}".format(len(s2)))
Output:
s2_length = 18
9.str.startswith()
str.startswith(substr,strbeg,strend) 判断原字符串是否以子字符串开头 可以用切片的形式进行判断(以顾头不顾尾为原则),这里的strend要比strbeg大否则传回false 函数结果返回一个布尔值
print("s.startswith() = {function}".format(function = s.startswith('ab'))) print("s.startswith() = {function}".format(function = s.startswith('D',2))) print("s.startswith() = {function}".format(function = s.startswith('c',2,5))) print("s.startswith() = {function}".format(function = s.startswith('c',2,100)))
Output:
#s = abcaDa a s.startswith() = True s.startswith() = False s.startswith() = True s.startswith() = True
10.str.endswith()
str.endswith(substr,strbeg,strend) 判断字符串是否以子字符串结尾 结果返回布尔值,这里的strend要比strbeg小否则传回false 和startswith()一样要从左到右为原则
print("s.endswith() = {function}".format(function = s.endswith('Da a'))) print("s.endswith() = {function}".format(function = s.endswith('a',-1))) print("s.endswith() = {function}".format(function = s.endswith('Da a',-4))) print("s.endswith() = {function}".format(function = s.endswith('c',-8,-5))) print("s.endswith() = {function}".format(function = s.endswith('c',-7,-5))) print("s.endswith() = {function}".format(function = s.endswith('c',-7,-4))) print("s.endswith() = {function}".format(function = s.endswith('Da a',-1,6)))
Output:
#s = abcaDa a s.endswith() = True s.endswith() = True s.endswith() = True s.endswith() = True s.endswith() = True s.endswith() = False s.endswith() = False
11.str.find()
str.find(substr,strbeg,strend) 寻找字符串中是否存在该子字符串并返回其索引,找不到则返回-1 若同时出现相同的字符串则返回最先找到
的子字符串索引,切片(遵循顾头不顾尾原则)
print("s.find() = {function}".format(function = s.find('a'))) print("s.find() = {function}".format(function = s.find('ab'))) print("s.find() = {function}".format(function = s.find('f'))) print("s.find() = {function}".format(function = s.find('b',-8,-5))) print("s.find() = {function}".format(function = s.find('b',0)))
Output:
s.find() = 0 s.find() = 0 s.find() = -1 s.find() = 1 s.find() = 1
12.str.index()
str.index(substr,strbeg,strend) 与find()的功能大致相同，但子字符串不存在于字符串中就会报错,结果返回索引
print("s.index() = {function}".format(function = s.index('a'))) print("s.index() = {function}".format(function = s.index('ab'))) print("s.index() = {function}".format(function = s.index('D',-8,5))) print("s.index() = {function}".format(function = s.index('b',0)))
Output:
#s = abcaDa a s.index() = 0 s.index() = 0 s.index() = 4 s.index() = 1
13.str.strip()
str.strip([chars]) 去掉字符串中首和尾的字符 默认删除的是空格 chars可以自行更改
print("s3.strip() = {function}".format(function = s3.strip()))
Output:
#s3 = as b123 s3.strip() = as b123
14.str.rstrip()
str.rstrip([chars]) 去掉字符串右边的字符 默认删除的是空格 返回值为删除后的新字符串
print("s4.rstrip() = {function}".format(function = s4.rstrip())) print("s4.rstrip() = {function}".format(function = s4.rstrip('# c')))
Output:
#s4 = ' &abc123 c ## ' s4.rstrip() = &abc123 c ## s4.rstrip() = &abc123
15.str.lstrip()
str.lstrip([chars]) 去掉字符串左边的字符 默认删除的是空格 返回值为删除后的新字符串
print("s4.lstrip() = {function}".format(function = s4.lstrip())) print("s4.lstrip() = {function}".format(function = s4.lstrip(' &')))
Output:
#s4 = ' &abc123 c ## ' s4.lstrip() = &abc123 c ## s4.lstrip() = abc123 c ##
16.str.count()
str.count(substr,start,end) start为第一个字符，这里默认为0 end未结束搜索的位置,默认为len(s) 主要功能统计字符串中某个字符出现
的个数并返回个数
print("s.count() = {function}".format(function = s.count('a'))) print("s.count() = {function}".format(function = s.count('Fa'))) print("s.count() = {function}".format(function = s.count('a',-7)))
Output:
#s = "abcaDa a" s.count() = 4 s.count() = 0 s.count() = 3
17.str.split()
str.split(substr = " ",num = s.count(str)) 主要作用分割字符串 这里的substr默认以空格分割,num为总共切割的次数,若num有数值怎分割num+1个字符串 分割后将字符串转化为list形式 substr会在分割后消失
print("s2.split() = {function}".format(function = s2.split())) print("s2.split() = {function}".format(function = s2.split(' ',0))) print("s2.split() = {function}".format(function = s2.split('a',1))) print("s2.split() = {function}".format(function = s2.split('a',-1)))
Output:
#s2 = "123a abc ABCSAa s " s2.split() = ['123a', 'abc', 'ABCSAa', 's'] s2.split() = ['123a abc ABCSAa s '] s2.split() = ['123', ' abc ABCSAa s '] s2.split() = ['123', ' ', 'bc ABCSA', ' s ']
18.str.format()
三种用法：
print("s = {}|s2 = {}|s3 = {}".format(s,s2,s3)) print("s = {0}|s2 = {1}|s3 = {2}|s = {0}|s3 = {2}".format(s,s2,s3)) print("s = {s}{sep}s2 = {s2}{sep}s3 = {s3}".format(s = s,s2 = s2,s3 = s3,sep = '|'))
Output:
s = abcaDa a|s2 = 123a abc ABCSAa s |s3 = as b123 s = abcaDa a|s2 = 123a abc ABCSAa s |s3 = as b123|s = abcaDa a|s3 = as b123 s = abcaDa a|s2 = 123a abc ABCSAa s |s3 = as b123
当占位符不按顺序写会报错 tuple index out of range
19.str.replace()
s.replace(old,new,max) old为将被替换的字符串,new为替换old的字符串,max为替换次数将字符串进行替换,若old未存在原字符串内则返回原
字符串
print("s.replace() = {function}".format(function = s.replace('ac','A'))) print("s.replace() = {function}".format(function = s.replace('a','A'))) print("s.replace() = {function}".format(function = s.replace('a','A',2)))
Output:
#s = "abcaDa a" s.replace() = abcaDa a s.replace() = AbcADA A s.replace() = AbcADa a
20.is函数
str.isalnum() #判断是否由数字或字母组成
str.isalpha() #判断是否含有字母
str.isdecimal() #判断是否含有十进制数字
str.isdigit() #判断是否含有数字
str.islower() #判断是否含有小写字母
str.isupper() #判断是否含有大写字母
str.isnumeric() #判断是否只包含数字字符
str.isspace() #判断是否只含有空格
str.istitle() #判断是否经过title()函数处理过后的标题
21.join()
str.join(sequence) sequence为要连接的元素序列,函数作用是将指定字符串与原字符串中每一个字符一一连接
s = 'alex' print('&&'.join(s)) #a&&l&&e&&x l = ['a','l','e','x'] print('+'.join(l)) #a+l+e+x t = ('a','b') print('*'.join(t)) #a*b
PS:String索引对应