python教程-（三）使用字符串

一、设置字符串的格式：精简版

方法1

>>> format = "Hello %s, welcome to %s"
>>> values = ("tom", "shanghai")
>>> format % values
'Hello tom, Welcome to shanghai'

方法2

>>> from string import Template
>>> tmpl = Template("Hello $who, Welcome to $where")
>>> tmpl.substitute(who="tom", where="shanghai")
'Hello tom, Welcome to shanghai'

方法3

#无名称无索引
>>> "{},{} and {}".format("first", "second","third")
'first, second and third'
#有索引
>>> "{1},{0} and {2}".format("second","first","third")
'first, second and third'
#有名字
>>> from math import pi
>>> "{name} is approximately {value:.2f}".format(name="π",value=pi)
'π is approximately 3.14'

二、设置字符串的格式：完整版

1.替换字段名

>>>"{foo}, {}, {}, {bar}".format(5,4,foo=6,bar=9)
'6, 5, 4, 9'

>>>"{foo}, {1}, {0}, {bar}".format(5,4,foo=6,bar=9)
'6, 4, 5, 9'

>>> familyname = ["liu", "zhang"]
>>> "Mr {name[0]}".format(name=familyname)
'Mr liu'

2.基本转换

s、r和a分别使用str、repr和ascii进行转换

>>> print("{pi!s} {pi!r} {pi!a}".format(pi="π"))
π 'π' '\u03c0'

可指定转换为的类型

#转为8进制

>>> "the number is {num:o}".format(num=60)
'the number is 74'

#转为百分数
>>> "the number is {num:%}".format(num=60)
'the number is 6000.000000%'

#转为小数，用f
>>> "the number is {num:.2f}".format(num=60)
'the number is 60.00'

#转为十六进制，用x
>>> "the number is {num:x}".format(num=60)
'the number is 3c'

#转为二进制 用b
>>> "the number is {num:b}".format(num=60)
'the number is 111100'

3.宽度、精度和千位分割符

#设置宽度
>>> "{num:10}".format(num=3)
'         3'
>>> "{str:10}".format(str="abc")
'abc       '

#设置精度
>>> from math import pi
>>> "Pi day is {pi:.2f}".format(pi=pi)
'Pi day is 3.14'

#设置宽度和精度
>>> from math import pi
>>> "Pi day is {pi:10.2f}".format(pi=pi)
'Pi day is       3.14'

#设置千分位分割符用逗号
>>> "the price of TV is {:,}".format(3689)
'the price of TV is 3,689'

4.符号、对齐和用0填充

#用0填充，宽度保持10位，2位小数
>>> from math import pi
>>> "{:010.2f}".format(pi)
'0000003.14'

#左对齐用<
>>> print('{:<10.2f}'.format(pi))
3.14
#居中用^
>>> print('{:^10.2f}'.format(pi))
   3.14
#右对齐用>
>>> print('{:>10.2f}'.format(pi))
      3.14

#制定填充字符π
>>> print('{:π^10.2f}'.format(pi))
πππ3.14πππ

#等号=制定填充字符位于符号和数字中间
>>> print('{:=10.2f}'.format(-pi))
-     3.14
>>> print('{:10.2f}'.format(-pi))
     -3.14

三、字符串方法

#center，字符串两边添加填充字符
>>> "wolaile".center(10)
' wolaile  '
#center，字符串两边添加填充字符，指定字符#
>>> "wolaile".center(10, "#")
'#wolaile##'
>>> 

#find方法，在给定的字符串中查找子串，找到返回index
>>> "wolaile".find("ai")
3
#find方法，找不到返回-1
>>> "wolaile".find("aia")
-1

#find方法指定起点和终点，第二个参数起点，第三个参数终点
>>> "wolaile shanghai nihao".find("ha",9)
9
>>> "wolaile shanghai nihao".find("ha",10)
13
>>> "wolaile shanghai nihao".find("ha",10,11)
-1

#join用于合并序列的元素，跟split相反
>>> seq=['1','2','3','4','5']
>>> sep='+'
>>> sep.join(seq)
'1+2+3+4+5'

>>> dirs = '','usr','bin','env'
>>> dirs
('', 'usr', 'bin', 'env')
>>> '/'.join(dirs)
'/usr/bin/env'

#lower用于返回字符串的小写
>>> "WOLAILE".lower()
'wolaile'

#title 用于首字符大写（单词分割可能会有问题）
>>> "that's all folks".title()
"That'S All Folks"

#capwords也是用于首字符大写
>>> import string
>>> string.capwords("this's a cat")
"This's A Cat"

#replace 替换
>>> "this is a cat".replace("cat", "dog")
'this is a dog'

#split  用于分割，与join相反
>>> '/usr/bin/env'.split("/")
['', 'usr', 'bin', 'env']

#strip 删除字符串的开头和结尾的空白，中间的忽略
>>> "         biu   biu          ".strip()
'biu   biu'
#strip还可以删除字符串中首尾指定的字符
>>> "###haha  # biu $ biu$$$".strip("#$")
'haha  # biu $ biu'

#translate 作用类似replace，效率比replace高，使用前需创建转换表
>>> table = str.maketrans("cs","kz")
>>> table
{99: 107, 115: 122}
>>> "this is an incredible test".translate(table)
'thiz iz an inkredible tezt'