Python学习日记(一) String函数使用

s = "abcaDa a"
s2 = "123a abc ABCSAa s "
s3 = "\tas \t\tb123"
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\t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 = "\tas \t\tb123"
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() = ['', ' abc ABCSAa s ']
s2.split() = ['', ' ', '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