011 字符串的内置方法 三

encode(encoding='utf-8', errors='strict')

• 释义
  • encoding: 指定编码格式，默认为 utf-8
  • errors
    • 设置不同错误的处理方案，默认为 strict，意为编码错误引起一个 UnicodeError
    • 其他的值：ignore, replace, xmlcharrefreplace, backslashreplace
    • 还可以通过 codecs.register_error() 注册值

>>> s = "YorkFish不是鱼"
>>> utf8 = s.encode()
>>> utf8
b'YorkFishxe4xb8x8dxe6x98xafxe9xb1xbc'
>>> utf8.decode()
'YorkFish不是鱼'
>>> 
>>> gbk = s.encode("gbk")
>>> gbk
b'YorkFishxb2xbbxcaxc7xd3xe3'
>>> gbk.decode("gbk")
'YorkFish不是鱼'
>>> 

expandtabs([tabsize=8])

• 释义：
  • 将字符串中的 转换为空格
  • 如果不指定参数，默认 1 个制表符转 8 个空格

>>> s = "a tab: "
>>> s
'a tab:	'
>>> s.expandtabs()
'a tab:  '
>>> s.expandtabs(16)
'a tab:          '
>>> 

顺便补上 print()

• print(value, ..., sep=' ', end=' ', file=sys.stdout, flush=False)
• 默认情况下，将值打印到流或 sys.stdout
• 关键字参数
  • file: 类似于文件的对象（流）；默认为当前的 sys.stdout
  • sep: 在值之间插入的字符串，默认为空格
  • end: 在最后一个值后追加的字符串，默认为换行符
  • flush: whether to forcibly flush the stream 是否强制刷新数据流

first = "York"
last = "Fish"

print(first + last)
print(first, last, sep='')
print(first, last)
print()
print("YorkFish", end='

')
print(first, end='-')
print(last)

>>>

YorkFish
YorkFish
York Fish

YorkFish

York-Fish

format_map()

• 释义：在给定的字典中找对应的值

例1 官网的例子

class Default(dict):
     def __missing__(self, key):
         return key


print('{name} was born in {country}'.format_map(Default(name='Guido')))

>>>

Guido was born in country

例2

>>> d = {"name": "YorkFish", "language": "Python"}
>>> "{name} is learning {language}.".format_map(d)
'YorkFish is learning Python.'
>>> 

replace(old, new[, count])

• 释义
  • 用 new 替换 old，有多少换多少
  • 如果指定 count，则替换不超过 count 次

>>> s = "All things in their being are good for something."
>>> s.replace('i', 'I')
'All thIngs In theIr beIng are good for somethIng.'
>>> s.replace('i', 'I', 3)
'All thIngs In theIr being are good for something.'
>>> 

split(sep=None, maxsplit=-1)

• 释义
  • 以 sep 分割字符串
  • 默认以空格为分割符，有个陷阱，见例2
  • 如果设置了 maxsplit，则仅分割 maxsplit 次

例1

>>> "Y.o.r.k.F.i.s.h".split('.')
['Y', 'o', 'r', 'k', 'F', 'i', 's', 'h']
>>> "Y.o.r.k.F.i.s.h.".split('.')
['Y', 'o', 'r', 'k', 'F', 'i', 's', 'h', '']
>>> "Y.o.r.k.F.i.s.h".split('.', maxsplit=4)
['Y', 'o', 'r', 'k', 'F.i.s.h']
>>> 

例2

>>> " yorkfisih".split()
['yorkfisih']
>>> 
>>> " yorkfisih".split(' ')
['', 'yorkfisih']
>>> 
>>> ''.split(' ')  # n 个空格会被分为 n+1 个部分
['']
>>> ' '.split(' ')
['', '']
>>> '  '.split(' ')
['', '', '']
>>> 

• rsplit(sep=None, maxsplit=-1) 用法类似，从右边开始分割

splitlines([keepends])

• 释义
  • 按照 分隔，返回一个包含各行作为元素的列表
  • 若 keepends 为 True，则保留换行符

例1

>>> s = "Cease to struggle 
and you cease to live.
(Thomas Carlyle)"
>>> s.splitlines()
['Cease to struggle ', 'and you cease to live.', '(Thomas Carlyle)']
>>> s.splitlines(True)
['Cease to struggle 
', 'and you cease to live.
', '(Thomas Carlyle)']
>>> 

例2 splitlines() 与 split()

>>> ''.splitlines()
[]
>>> ''.split('
')
['']
>>> "love at first sight.
".splitlines()
['love at first sight.']
>>> "love at first sight.
".split('
')
['love at first sight.', '']

startswith(prefix[, start[, end]])

• 释义
  • 检查字符串是否以指定前缀 prefix 开头
  • 返回 True or False

>>> s = "The best is yet to come."
>>> s.startswith("The")
True
>>> s.startswith("is", 9)
True
>>> s.startswith("best", 4, 8)  # [4, 8)
True
>>> s.startswith("best", 4, 7)
False
>>> 

• endswith(sub[, start[, end]]) 见第一弹

swapcase()

• 释义：翻转字符串中的大小写

>>> "YorkFish".swapcase()
'yORKfISH'
>>> 

title()

• 释义
  • 返回“标题化”的字符串
  • Python 只是单纯地使每个词的首字母大写，非首字母小写
  • 对标题而言，比如介词要保持原样，这个 title() 没有实现

>>> "the great gatsby".title()
'The Great Gatsby'
>>> 

zfill(width)

• 释义
  • 必须填 width，否则会抛异常
  • 返回长度为 width 的字符串
  • 原字符串右对齐
  • 若 width 大于字符串长度，前边用 0 填充

>>> name = "YorkFish"
>>> name.zfill(5)
'YorkFish'
>>> name.zfill(10)
'00YorkFish'