Python正则表达式Regular Expression初探

目录

Regular

匹配规则

单字符匹配

 数量匹配

边界匹配

 分组匹配

贪婪与懒惰

原版说明

特殊字符

转义序列

模块方法

函数说明

匹配模式

常用匹配规则

1. 匹配出所有整数

2. 匹配11位且13开头的整数

Regular

Python的re模块提供了完整的正则表达式功能。正则表达式（Regular Expression）是一种强大的文本模式匹配工具，它能高效地进行查找、替换、分割等复杂字符串操作。

在Python中，通过 import re 即可引入这一神器。

匹配规则

单字符匹配

 数量匹配

边界匹配

 分组匹配

贪婪与懒惰

原版说明

特殊字符

    The special characters are:
        “.”      Matches any character except a newline.
        “^”      Matches the start of the string.
        “$”      Matches the end of the string or just before the newline at
                 the end of the string.
        “*”      Matches 0 or more (greedy) repetitions of the preceding RE.
                 Greedy means that it will match as many repetitions as possible.
        “+”      Matches 1 or more (greedy) repetitions of the preceding RE.
        “?”      Matches 0 or 1 (greedy) of the preceding RE.
        *?,+?,?? Non-greedy versions of the previous three special characters.
        {m,n}    Matches from m to n repetitions of the preceding RE.
        {m,n}?   Non-greedy version of the above.
        “\”     Either escapes special characters or signals a special sequence.
        []       Indicates a set of characters.
                 A “^” as the first character indicates a complementing set.
        “|”      A|B, creates an RE that will match either A or B.
        (…)    Matches the RE inside the parentheses.
                 The contents can be retrieved or matched later in the string.
        (?aiLmsux) The letters set the corresponding flags defined below.
        (?:…)  Non-grouping version of regular parentheses.
        (?P<name>…) The substring matched by the group is accessible by name.
        (?P=name)     Matches the text matched earlier by the group named name.
        (?#…)  A comment; ignored.
        (?=…)  Matches if … matches next, but doesn’t consume the string.
        (?!…)  Matches if … doesn’t match next.
        (?<=…) Matches if preceded by … (must be fixed length).
        (?<!…) Matches if not preceded by … (must be fixed length).
        (?(id/name)yes|no) Matches yes pattern if the group with id/name matched,
                           the (optional) no pattern otherwise.

转义序列

    The special sequences consist of “\” and a character from the list
    below.  If the ordinary character is not on the list, then the
    resulting RE will match the second character.
        number  Matches the contents of the group of the same number.
        A       Matches only at the start of the string.
        Z       Matches only at the end of the string.
        b       Matches the empty string, but only at the start or end of a word.
        B       Matches the empty string, but not at the start or end of a word.
        d       Matches any decimal digit; equivalent to the set [0-9] in
                 bytes patterns or string patterns with the ASCII flag.
                 In string patterns without the ASCII flag, it will match the whole
                 range of Unicode digits.
        D       Matches any non-digit character; equivalent to [^d].
        s       Matches any whitespace character; equivalent to [ tnrfv] in
                 bytes patterns or string patterns with the ASCII flag.
                 In string patterns without the ASCII flag, it will match the whole
                 range of Unicode whitespace characters.
        S       Matches any non-whitespace character; equivalent to [^s].
        w       Matches any alphanumeric character; equivalent to [a-zA-Z0-9_]
                 in bytes patterns or string patterns with the ASCII flag.
                 In string patterns without the ASCII flag, it will match the
                 range of Unicode alphanumeric characters (letters plus digits
                 plus underscore).
                 With LOCALE, it will match the set [0-9_] plus characters defined
                 as letters for the current locale.
        W       Matches the complement of w.
        \       Matches a literal backslash.

模块方法

    This module exports the following functions:
        match     Match a regular expression pattern to the beginning of a string.
        fullmatch Match a regular expression pattern to all of a string.
        search    Search a string for the presence of a pattern.
        sub       Substitute occurrences of a pattern found in a string.
        subn      Same as sub, but also return the number of substitutions made.
        split     Split a string by the occurrences of a pattern.
        findall   Find all occurrences of a pattern in a string.
        finditer  Return an iterator yielding a Match object for each match.
        compile   Compile a pattern into a Pattern object.
        purge     Clear the regular expression cache.
        escape    Backslash all non-alphanumerics in a string.

函数说明

match(pattern, string, flags=0)
    Try to apply the pattern at the start of the string, returning
    a Match object, or None if no match was found.

fullmatch(pattern, string, flags=0)
    Try to apply the pattern to all of the string, returning
    a Match object, or None if no match was found.

search(pattern, string, flags=0)
    Scan through string looking for a match to the pattern, returning
    a Match object, or None if no match was found.

sub(pattern, repl, string, count=0, flags=0)
    Return the string obtained by replacing the leftmost
    non-overlapping occurrences of the pattern in string by the
    replacement repl.  repl can be either a string or a callable;
    if a string, backslash escapes in it are processed.  If it is
    a callable, it’s passed the Match object and must return
    a replacement string to be used.

subn(pattern, repl, string, count=0, flags=0)
    Return a 2-tuple containing (new_string, number).
    new_string is the string obtained by replacing the leftmost
    non-overlapping occurrences of the pattern in the source
    string by the replacement repl.  number is the number of
    substitutions that were made. repl can be either a string or a
    callable; if a string, backslash escapes in it are processed.
    If it is a callable, it’s passed the Match object and must
    return a replacement string to be used.

split(pattern, string, maxsplit=0, flags=0)
    Split the source string by the occurrences of the pattern,
    returning a list containing the resulting substrings.  If
    capturing parentheses are used in pattern, then the text of all
    groups in the pattern are also returned as part of the resulting
    list.  If maxsplit is nonzero, at most maxsplit splits occur,
    and the remainder of the string is returned as the final element
    of the list.

findall(pattern, string, flags=0)
    Return a list of all non-overlapping matches in the string.

    If one or more capturing groups are present in the pattern, return
    a list of groups; this will be a list of tuples if the pattern
    has more than one group.

    Empty matches are included in the result.

finditer(pattern, string, flags=0)
    Return an iterator over all non-overlapping matches in the
    string.  For each match, the iterator returns a Match object.

    Empty matches are included in the result.

compile(pattern, flags=0)
    Compile a regular expression pattern, returning a Pattern object.

purge()
    Clear the regular expression caches

escape(pattern)
    Escape special characters in a string.

匹配模式

    Each function other than purge and escape can take an optional ‘flags’ argument
    consisting of one or more of the following module constants, joined by “|”.
    A, L, and U are mutually exclusive.
        A  ASCII       For string patterns, make w, W, b, B, d, D
                       match the corresponding ASCII character categories
                       (rather than the whole Unicode categories, which is the
                       default).
                       For bytes patterns, this flag is the only available
                       behaviour and needn’t be specified.
        I  IGNORECASE  Perform case-insensitive matching.
        L  LOCALE      Make w, W, b, B, dependent on the current locale.
        M  MULTILINE   “^” matches the beginning of lines (after a newline)
                       as well as the string.
                       “$” matches the end of lines (before a newline) as well
                       as the end of the string.
        S  DOTALL      “.” matches any character at all, including the newline.
        X  VERBOSE     Ignore whitespace and comments for nicer looking RE’s.
        U  UNICODE     For compatibility only. Ignored for string patterns (it
                       is the default), and forbidden for bytes patterns.

常用匹配规则

掌握正则的关键是根据规则来编写匹配样式，下面列出一些常用的Regular pattern：

1. 匹配出所有整数

>>> import re
>>> pat = ‘d+’
>>> txt = ‘No.123;Tel:1396260000’
>>> re.findall(pat, txt)
[‘123’, ‘1396260000’]

2. 匹配11位且13开头的整数

注意r’13d{9}’，13开头余下的9位数字用d{9}表示

>>> import re
>>> txt = ”’
… 001:13962600001
… 002:1330626001
… 003:18962600002
… 004:13106260003
… 005:16605200006
… ”’
>>> pat = r’13d{9}’
>>> re.findall(pat, txt)
[‘13962600001’, ‘13106260003’]

……

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