Python：字符串处理函数

split() / join() 拆分和组合

#split() 通过指定分隔符对字符串进行切片（拆分）,默认空格符
lan = "python ruby c c++ swift"
lan.split()
#['python', 'ruby', 'c', 'c++', 'swift']

#传入符号','
todos = "download python, install, download ide, learn"
todos.split(', ')
#['download python', 'install', 'download ide', 'learn']

#把它们组合成字符串
','.join(['download python', 'install', 'download ide', 'learn'])
#'download python,install,download ide,learn'

replace() 替换

#replace() 第三个参数为代替几个
s = 'I like C. I like C++. I like Python'
s.replace('like', 'hate')
#'I hate C. I hate C++. I hate Python'

s.replace('like', 'hate', 1)
#'I hate C. I like C++. I like Python'

布局center() : 前后留空 ljust()：后面留空 rjust()：前面留空

align = 'Learn how to align'
align.center(30)
#'      Learn how to align      '

align.ljust(30)
#'Learn how to align            '

align.rjust(30)
#'            Learn how to align'

ralign = align.rjust(30)
ralign.strip()
#'Learn how to align'

 eval()： 将字符串处理为可以运算的类型

# eval()

str1 = '1+2'
print(str1)  #输出1+2

print(eval(str1))  #输出3

format() ：格式化字符串  （New style in Python 3.6）

format(输出项，[,格式化字符串])

格式化输出 1）利用字符串格式化运算符%。 格式化字符串%（输出项1，输出项2....）

%% 百分号

%s 字符串

%c 字符

%d 带符号整数 （10进制）

%o 带符号整数 （8进制）

%x或者%X 带符号整数（16进制）

%e或者%E 浮点数字（科学计数法）

%f或者%F 浮点数字（带小数点）

%g或者%G 根据大小来选择

%e %f %*.*f %（项1，项2，输出项） 例如 %*.*f%(6,2,3.145) 等同 %6.2f%3.145

#格式化字符串的函数 str.format()，它增强了字符串格式化的功能。基本语法是通过 {} 和 : 来代替以前的 %
print('%s %s' % ('one', 'two'))
print('{} {}'.format('one', 'two'))
print('%d %d' % (1, 2))
print('{} {}'.format(1, 2))
#one two
#one two
#1 2
#1 2

print('{1} {0}'.format('one', 'two'))
#two one

a = 5
b = 10
print(f'Five plus ten is {a + b} and not {2 * (a + b)}.')
#Five plus ten is 15 and not 30.

'''
格式字符串还可以指定填充字符、对齐方式（其中<表示左对齐，>表示右对齐、^表示居中、==代表填充字符位于 符号和数字之间）、符号（其中+表示正号，-表示负号）
'''
>>>format(65,"c")
A
>>>print(format(3.145,"6.2f"))
   3.15
>>>print(format(3.145,"-6.2f"))
   3.15
>>>print(format(3.145,"+6.2f"))
 +3.15
>>>print(format(3.145,"<6.2f"))
3.15
>>>print(format(3.145,">6.2f"))
   3.15
>>>print(format(3.145,"><6.2f"))
3.15>>
>>>print(format(3.145,"<=6.2f"))
<<3.15
>>>print(format(3.145,"=6.2f"))
   3.15
>>>print(format(3.145,"^6.2f"))
  3.15
>><print(format(3.145,"0=+10"))
+00003.145

 其他

#以下函数都是返回新的值，不影响原来的字符串
kk = "Python description: Python is a programming language that lets you work quickly and integrate systems more effectively."

kk.startswith('Python')
#True

kk.endswith('effectively.')
#True

kk.find('language')
#44

#检测字符串是否由字母和数字组成
kk.isalnum()  
#False

kk.count("Python")
#2

#移除字符串头尾指定的字符（默认为空格或换行符）或字符序列
kk.strip('.')
#'Python description: Python is a programming language that lets you work quickly and integrate systems more effectively'

kk.upper()
#'PYTHON DESCRIPTION: PYTHON IS A PROGRAMMING LANGUAGE THAT LETS YOU WORK QUICKLY AND INTEGRATE SYSTEMS MORE EFFECTIVELY.'

kk.lower()
#'python description: python is a programming language that lets you work quickly and integrate systems more effectively.'

kk.title()     
#每个单词开头都大写
#'Python Description: Python Is A Programming Language That Lets You Work Quickly And Integrate Systems More Effectively.'

kk.capitalize()   
#首个单词开头大写，后面不大写
#Python description: python is a programming language that lets you work quickly and integrate systems more effectively.

kk.swapcase()
#每个字母大小写调换
#pYTHON DESCRIPTION: pYTHON IS A PROGRAMMING LANGUAGE THAT LETS YOU WORK QUICKLY AND INTEGRATE SYSTEMS MORE EFFECTIVELY.