Pythonのreモジュール

Pythonのreモジュール
Pythonではperlスタイルの正規表現モードを提供し、reモジュールはPythonにすべての正規表現機能を持たせる.
compile関数は、モード文字列とオプションフラグパラメータに基づいて、正規表現のマッチングと置換のための一連の方法を持つ正規表現オブジェクトを生成します.
reモジュールは、これらの方法の機能と完全に一致する関数を提供し、これらの関数は、モード文字列を最初のパラメータとして使用します.
本文はreモジュールの主な関数と使い方を紹介する.
re.pyの特殊文字の定義

r"""
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.
    "*"        0     （  ）。               
             
    "+"      Matches 1 or more (greedy) repetitions of the preceding RE.
    "+"        1    。
    "?"      Matches 0 or 1 (greedy) of the preceding RE.
    "?"            1  0
    *?,+?,?? 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) Set the A, I, L, M, S, U, or X flag for the RE (see below).
    (?:...)  Non-grouping version of regular parentheses.
    (?P...) 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).
    (?

pythonのreモジュールには、次の関数があります.

r"""
    match     Match a regular expression pattern to the beginning of a string.
    match                  。
    fullmatch Match a regular expression pattern to all of a string.
    fullmatch               
    search    Search a string for the presence of a pattern.
    search    
    sub       Substitute occurrences of a pattern found in a string.
    sub             
    subn      Same as sub, but also return the number of substitutions made.
    subn       sub  ，           
    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 RegexObject.
    purge     Clear the regular expression cache.
    escape    Backslash all non-alphanumerics in a string."""

このモジュールのいくつかの機能は、オプションのパラメータとしてフラグを使用します.

r"""
    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."""

reモジュールにも例外「エラー」が定義されています.