python之格式化字符串速记整理

it2022-05-06  3

 

一、格式化字符串的方式:

1、字符串表达式:

语法格式:‘%s’ % var 或 ‘%s %d’ % (var1, var2)

说明:%s、%d等为格式类型说明符

例子:

>>> 'this is a %s' % ('pear') 'this is a pear' >>> 'there are %d %s and %d %s' % (2, 'pear', 5, 'apple')'there are 2 pear and 5 apple'#使用字典格式 >>> 'there are %(count)d %(fruit)s' % {'count':5, 'fruit':'apples'} 'there are 5 apples'

 

2、字符串format方法:

语法格式:str.format()

说明:使用字符串的format方法

例子:

#使用相对位置参数>>> astring = 'there are {} {} and {} {}' >>> astring.format(2, 'pears', 5, 'apples') 'there are 2 pears and 5 apples'#使用绝对位置参数 >>> astring = 'there are {0} {1} and {0} {2}' >>> astring.format(2, 'pears', 'apples') 'there are 2 pears and 2 apples'#使用关键字参数 >>> astring = 'there are {count} {fruit1} and {count} {fruit2}'>>> astring.format(count=2, fruit1='pears', fruit2='apples')'there are 2 pears and 2 apples'

 

3、format内建函数:

语法格式:format(value[, format_spec])

说明:第1个参数为字符串、数字等,第2个参数为格式说明符,省略格式说明符,就相当于str(value)

例子:

#缺省类型为s(字符串),可以省略不写>>> format('^表示居中,10表示宽度,不够的位用#填充','#^10') '^表示居中,10表示宽度,不够的位用#填充' >>> format(123,'b') '1111011' >>> format(123,'#b') '0b1111011' >>>

 

4、已格式化的字符串直接量(也就是一个带格式的字符串,简称f-strings):

语法格式:f'{expression[:format-spicifier]}'

说明:类似于r'string'、b'byte sequence'的风格,f也可以是大写的F,表达式expression可以是直接量、变量,对象属性,函数调用、模块方法执行等,还可以结合!s或!r对表示执行str或repr函数。格式化说明符可以省略。

例子:

>>> f'{10:b}' '1010' >>> f'{10:x}' 'a' >>> f'{12:x}' 'c' >>> f'{12:X}' 'C' >>> f'{12:#X}' '0XC' >>> f'{12:02X}' '0C' >>> f'{12:2X}' ' C' >>> F'this is a hex number {12:#2X} and an octet number {29:#o}' 'this is a hex number 0XC and an octet number 0o35' >>> import random >>> F'this is a hex number {random.randint(100,500):#2X} and an octet number {29:#o}' 'this is a hex number 0X8A and an octet number 0o35' >>> import math >>> print(f'The value of pi is approximately {math.pi:.3f}.') The value of pi is approximately 3.142. #表示式为变量,效果类似于shell字符串中变量替换,同时还可以在替换后进行格式化>>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678} >>> for name, phone in table.items(): ... print(f'{name:10} ==> {phone:10d}') ... Sjoerd ==> 4127 Jack ==> 4098 Dcab ==> 7678 >>> animals = 'eels' >>> print(f'My hovercraft is full of {animals}.') My hovercraft is full of eels. >>> print(f'My hovercraft is full of {animals!r}.') My hovercraft is full of 'eels'.

 

5、字符串手动格式化

语法格式:str.rjust([width][, padding-char])、str.rjust([width][, padding-char])、center([width][, padding-char])、str.zfill()

说明:字符串的左、右、中对齐方法,第1个参数为宽度,第2个为字符串宽度小于指定宽度后填充的字符,缺省为空格。str.zfill()用于数字串填充0

例子:

>>> '12'.zfill(5) '00012' >>> '-3.14'.zfill(7) '-003.14' >>> '3.14159265359'.zfill(5) '3.14159265359' >>> 'this is a left indent string'.ljust(40) 'this is a left indent string ' >>> 'this is a left indent string'.ljust(40,'-') 'this is a left indent string------------' >>>

 

二、通用标准格式化说明符及特殊格式说明符如下:

format_spec ::= [[fill]align][sign][#][0][width][grouping_option][.precision][type] fill ::= <any character> align ::= "<" | ">" | "=" | "^" sign ::= "+" | "-" | " " width ::= digit+ grouping_option ::= "_" | ","precision ::= digit+ type ::= "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X"

 

 旧的字符串表达式格式:

>>> '%#x' % 255, '%x' % 255, '%X' % 255 ('0xff', 'ff', 'FF') >>> format(255, '#x'), format(255, 'x'), format(255, 'X') ('0xff', 'ff', 'FF') >>> f'{255:#x}', f'{255:x}', f'{255:X}' ('0xff', 'ff', 'FF')

 

表示一个百分号%使用特殊类型符%:

>>> points = 19 >>> total = 22 >>> 'Correct answers: {:.2%}'.format(points/total) 'Correct answers: 86.36%'

 

 

使用时间专用格式:

>>> import datetime >>> d = datetime.datetime(2010, 7, 4, 12, 15, 58) >>> '{:%Y-%m-%d %H:%M:%S}'.format(d) '2010-07-04 12:15:58'

 

嵌套参数和更复杂例子:

>>> for align, text in zip('<^>', ['left', 'center', 'right']): ... '{0:{fill}{align}16}'.format(text, fill=align, align=align) ... 'left<<<<<<<<<<<<' '^^^^^center^^^^^' '>>>>>>>>>>>right' >>> >>> octets = [192, 168, 0, 1] >>> '{:02X}{:02X}{:02X}{:02X}'.format(*octets) 'C0A80001' >>> int(_, 16) 3232235521 >>> >>> width = 5 >>> for num in range(5,12): ... for base in 'dXob': ... print('{0:{width}{base}}'.format(num, base=base, width=width), end=' ') ... print() ... 5 5 5 101 6 6 6 110 7 7 7 111 8 8 10 1000 9 9 11 1001 10 A 12 1010 11 B 13 1011

 

更详细的格式化说明可以参见python3.7.1参考手册的章节:7.1. Fancier Output Formatting

 

转载于:https://www.cnblogs.com/dingbj/p/format.html


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