字符串不仅支持所有通用序列操作，还实现了很多附件方法。
我会以『字符串方法』为标题，分几篇笔记逐一介绍这些方法。
我会在这仓库中持续更新笔记：https://github.com/orca-j35/python_notes
translate
🔨 str.translate(table)
Return a copy of the string in which each character has been mapped through the given translation table. The table must be an object that implements indexing via __getitem__(), typically a mapping or sequence. When indexed by a Unicode ordinal (an integer), the table object can do any of the following: return a Unicode ordinal or a string, to map the character to one or more other characters; return None, to delete the character from the return string; or raise a LookupError exception, to map the character to itself.
# 该方法会按照table将字符串中的字符映射为指定的字符或字符串
# 在table中需使用码点作为键或索引
>>> table = {ord('a'): '#', ord('b'): '$$'}
>>> 'abcdabcd'.translate(table)
'#$$cd#$$cd'
# 在table中值为None，将被删除
>>> table = {ord('a'): '#', ord('b'): '$$',ord('c'):None}
>>> 'abcdabcd'.translate(table)
'#$$d#$$d'
You can use str.maketrans() to create a translation map from character-to-character mappings in different formats.
See also the codecs module for a more flexible approach to custom character mappings.
如果想要了解更多自定义字符映射的方法，可以查看 codecs 模块。
maketrans
🔨 static str.maketrans(x[, y[, z]])
This static method returns a translation table usable for str.translate().
If there is only one argument, it must be a dictionary mapping Unicode ordinals (integers) or characters (strings of length 1) to Unicode ordinals, strings (of arbitrary lengths) or None. Character keys will then be converted to ordinals.
If there are two arguments, they must be strings of equal length, and in the resulting dictionary, each character in x will be mapped to the character at the same position in y. If there is a third argument, it must be a string, whose characters will be mapped to Nonein the result.
# 生成一个共str.translate()使用的table
# 如果使用单参数形式，则x必须是一个字典，
# 该字典的键是Unicode码点或单个字符；该字典的值是码点或字符串或None，
# 如果键是字符，str.maketrans最终也会将其转换为码点
>>> d={97:'!','b':'##','c':None} # a的码点是97
>>> str.maketrans(d)
{97: '!', 98: '##', 99: None}
>>> 'abc'.translate(str.maketrans(d))
'!##'
# 如果使用双参数形式，则x和y必须是长度相同的字符串,
# x中的字符被逐一用作table字典的键，y中的字符被逐一用作table字典的值
>>> str.maketrans('abc','!@#')
{97: 33, 98: 64, 99: 35}
>>> 'abc'.translate(str.maketrans('abc','!@#'))
'!@#'
# 如果使用三参数形式，x和y与双参数的含义与双参数形式相同；
# z必须是一个字符串，该字符串中的字符会被映射为None，值为None的字符将被删除
>>> str.maketrans('abc','!@#','cde')
{97: 33, 98: 64, 99: None, 100: None, 101: None}
>>> 'abcdefg'.translate(str.maketrans('abc','!@#','cde'))
'!@fg'
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