re.sub

官网文档：

  • 英文
    • re.sub — Regular expression operations — Python 3 documentation

      re.sub(pattern, repl, string, count=0, flags=0)

      Return the string obtained by replacing the leftmost non-overlapping occurrences of pattern in string by the replacement repl. If the pattern isn’t found, string is returned unchanged. repl can be a string or a function; if it is a string, any backslash escapes in it are processed. That is, \n is converted to a single newline character, \r is converted to a carriage return, and so forth. Unknown escapes of ASCII letters are reserved for future use and treated as errors. Other unknown escapes such as \& are left alone. Backreferences, such as \6, are replaced with the substring matched by group 6 in the pattern. For example:

      >> re.sub(r'def\s+([a-zA-Z_][a-zA-Z_0-9]*)\s*\(\s*\):',
...        r'static PyObject*\npy_\1(void)\n{',
...        'def myfunc():')
'static PyObject*\npy_myfunc(void)\n{'

      If repl is a function, it is called for every non-overlapping occurrence of pattern. The function takes a single match object argument, and returns the replacement string. For example:

      >> def dashrepl(matchobj):
...     if matchobj.group(0) == '-': return ' '
...     else: return '-'
>> re.sub('-{1,2}', dashrepl, 'pro----gram-files')
'pro--gram files'
>> re.sub(r'\sAND\s', ' & ', 'Baked Beans And Spam', flags=re.IGNORECASE)
'Baked Beans & Spam'

      The pattern may be a string or a pattern object.

      The optional argument count is the maximum number of pattern occurrences to be replaced; count must be a non-negative integer. If omitted or zero, all occurrences will be replaced. Empty matches for the pattern are replaced only when not adjacent to a previous empty match, so sub('x*', '-', 'abxd') returns '-a-b--d-'.

      In string-type repl arguments, in addition to the character escapes and backreferences described above, \g<name> will use the substring matched by the group named name, as defined by the (?P<name>...) syntax. \g<number> uses the corresponding group number; \g<2> is therefore equivalent to \2, but isn’t ambiguous in a replacement such as \g<2>0. \20 would be interpreted as a reference to group 20, not a reference to group 2 followed by the literal character '0'. The backreference \g<0> substitutes in the entire substring matched by the RE.

      • Change Log
        • Changed in version 3.1: Added the optional flags argument.
        • Changed in version 3.5: Unmatched groups are replaced with an empty string.
        • Changed in version 3.6: Unknown escapes in pattern consisting of '\' and an ASCII letter now are errors.
        • Changed in version 3.7: Unknown escapes in repl consisting of '\' and an ASCII letter now are errors.
        • Changed in version 3.7: Empty matches for the pattern are replaced when adjacent to a previous non-empty match.
  • 中文
    • re.sub --- 正则表达式操作 — Python 3 文档

      re.sub(pattern, repl, string, count=0, flags=0)

      返回通过使用 repl 替换在 string 最左边非重叠出现的 pattern 而获得的字符串。 如果样式没有找到，则不加改变地返回 string。 repl 可以是字符串或函数；如为字符串，则其中任何反斜杠转义序列都会被处理。 也就是说，\n 会被转换为一个换行符，\r 会被转换为一个回车附，依此类推。 未知的 ASCII 字符转义序列保留在未来使用，会被当作错误来处理。 其他未知转义序列例如 \& 会保持原样。 向后引用像是 \6 会用样式中第 6 组所匹配到的子字符串来替换。 例如:

      >> re.sub(r'def\s+([a-zA-Z_][a-zA-Z_0-9]*)\s*\(\s*\):',
...        r'static PyObject*\npy_\1(void)\n{',
...        'def myfunc():')
'static PyObject*\npy_myfunc(void)\n{'

      如果 repl 是一个函数，那它会对每个非重复的 pattern 的情况调用。这个函数只能有一个 匹配对象 参数，并返回一个替换后的字符串。比如

      >> def dashrepl(matchobj):
...     if matchobj.group(0) == '-': return ' '
...     else: return '-'
>> re.sub('-{1,2}', dashrepl, 'pro----gram-files')
'pro--gram files'
>> re.sub(r'\sAND\s', ' & ', 'Baked Beans And Spam', flags=re.IGNORECASE)
'Baked Beans & Spam'

      样式可以是一个字符串或者一个 样式对象 。

      可选参数 count 是要替换的最大次数；count 必须是非负整数。如果忽略这个参数，或者设置为0，所有的匹配都会被替换。空匹配只在不相临连续的情况被更替，所以 sub('x*', '-', 'abxd') 返回 '-a-b--d-' 。

      在字符串类型的 repl 参数里，如上所述的转义和向后引用中，\g<name> 会使用命名组合 name，（在 (?P<name>…) 语法中定义） \g<number> 会使用数字组；\g<2> 就是 \2，但它避免了二义性，如 \g<2>0。 \20 就会被解释为组20，而不是组2后面跟随一个字符 '0'。向后引用 \g<0> 把 pattern 作为一整个组进行引用。

      • 更新日志
        • 在 3.1 版更改: 增加了可选标记参数。
        • 在 3.5 版更改: 不匹配的组合替换为空字符串。
        • 在 3.6 版更改: pattern 中的未知转义（由 '\' 和一个 ASCII 字符组成）被视为错误。
        • 在 3.7 版更改: repl 中的未知转义（由 '\' 和一个 ASCII 字符组成）被视为错误。
        • 在 3.7 版更改: 样式中的空匹配相邻接时会被替换。

举例

把

最后更新：`20190825`

中的日期换成最新的，比如20200919

则可以用代码：

oldReamdMdStr = "最后更新：`20190825`"
newLastUpdateStr = "最后更新：`20200919`"
newReamdMdStr = re.sub("最后更新：`\d+`", newLastUpdateStr, oldReamdMdStr)

详细过程可参考：

  • 【已解决】给crifan的gitbook的template添加部署时更新github.io的README

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