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Python如何使用組合方式構(gòu)建復(fù)雜正則

更新時(shí)間：2024年12月02日 15:31:28 作者：韋易笑

在Python中正則寫(xiě)復(fù)雜了很麻煩,難寫(xiě)難調(diào)試,其實(shí)只需要兩個(gè)函數(shù),就能用簡(jiǎn)單正則組合構(gòu)建復(fù)雜正則,感興趣的小伙伴可以跟隨小編一起學(xué)習(xí)一下

正則寫(xiě)復(fù)雜了很麻煩，難寫(xiě)難調(diào)試，只需要兩個(gè)函數(shù)，就能用簡(jiǎn)單正則組合構(gòu)建復(fù)雜正則：

比如輸入一個(gè)字符串規(guī)則，可以使用 {name} 引用前面定義的規(guī)則：

# rules definition
rules = r'''
    protocol = http|https
    login_name = [^:@\r\n\t ]+
    login_pass = [^@\r\n\t ]+
    login = {login_name}(:{login_pass})?
    host = [^:/@\r\n\t ]+
    port = \d+
    optional_port = (?:[:]{port})?
    path = /[^\r\n\t ]*
    url = {protocol}://({login}[@])?{host}{optional_port}{path}?
'''

然后調(diào)用 regex_build 函數(shù)，將上面的規(guī)則轉(zhuǎn)換成一個(gè)字典并輸出：

# expand patterns in a dictionary
m = regex_build(rules, capture = True)

# list generated patterns
for k, v in m.items(): 
    print(k, '=', v)

結(jié)果：

protocol = (?P<protocol>http|https)
login_name = (?P<login_name>[^:@\r\n\t ]+)
login_pass = (?P<login_pass>[^@\r\n\t ]+)
login = (?P<login>(?P<login_name>[^:@\r\n\t ]+)(:(?P<login_pass>[^@\r\n\t ]+))?)
host = (?P<host>[^:/@\r\n\t ]+)
port = (?P<port>\d+)
optional_port = (?P<optional_port>(?:[:](?P<port>\d+))?)
path = (?P<path>/[^\r\n\t ]*)
url = (?P<url>(?P<protocol>http|https)://((?P<login>(?P<login_name>[^:@\r\n\t ]+)(:(?P<login_pass>[^@\r\n\t ]+))?)[@])?(?P<host>[^:/@\r\n\t ]+)(?P<optional_port>(?:[:](?P<port>\d+))?)(?P<path>/[^\r\n\t ]*)?)

用手寫(xiě)直接寫(xiě)是很難寫(xiě)出這么復(fù)雜的正則的，寫(xiě)出來(lái)也很難調(diào)試，而組合方式構(gòu)建正則的話，可以將小的簡(jiǎn)單正則提前測(cè)試好，要用的時(shí)候再組裝起來(lái)，就不容易出錯(cuò)，上面就是組裝替換后的結(jié)果。

下面用里面的 url 這個(gè)規(guī)則來(lái)匹配一下：

# 使用規(guī)則 "url" 進(jìn)行匹配
pattern = m['url']
s = re.match(pattern, 'https://name:pass@www.baidu.com:8080/haha')

# 打印完整匹配結(jié)果
print('matched: "%s"'%s.group(0))
print()

# 打印分組匹配結(jié)果
for name in ('url', 'login_name', 'login_pass', 'host', 'port', 'path'):
    print('subgroup:', name, '=', s.group(name))

輸出：

match text with pattern "url"
matched: "https://name:pass@www.baidu.com:8080/haha"

subgroup: url = https://name:pass@www.baidu.com:8080/haha
subgroup: login_name = name
subgroup: login_pass = pass
subgroup: host = www.baidu.com
subgroup: port = 8080
subgroup: path = /haha

可以取完整結(jié)果，也可以按照規(guī)則名字，取得里面具體某個(gè)部件得匹配結(jié)果。

這下可以方便的寫(xiě)復(fù)雜正則表達(dá)式了。

再 Python 的正則表達(dá)式里 {xxx} 是用來(lái)表示長(zhǎng)度的，里面都是數(shù)字，如果里面是變量名的話不會(huì)和原有規(guī)則沖突，因此這個(gè)寫(xiě)法是安全的。

實(shí)現(xiàn)代碼：

import re

# 將 pattern 里形如 {name} 的文本，用 macros 里的預(yù)定義規(guī)則替換
def regex_expand(macros, pattern, guarded = True):
    output = []
    pos = 0
    size = len(pattern)
    while pos < size:
        ch = pattern[pos]
        if ch == '\\':
            output.append(pattern[pos:pos + 2])
            pos += 2
            continue
        elif ch != '{':
            output.append(ch)
            pos += 1
            continue
        p2 = pattern.find('}', pos)
        if p2 < 0:
            output.append(ch)
            pos += 1
            continue
        p3 = p2 + 1
        name = pattern[pos + 1:p2].strip('\r\n\t ')
        if name == '':
            output.append(pattern[pos:p3])
            pos = p3
            continue
        elif name[0].isdigit():
            output.append(pattern[pos:p3])
            pos = p3
            continue
        elif ('<' in name) or ('>' in name):
            raise ValueError('invalid pattern name "%s"'%name)
        if name not in macros:
            raise ValueError('{%s} is undefined'%name)
        if guarded:
            output.append('(?:' + macros[name] + ')')
        else:
            output.append(macros[name])
        pos = p3
    return ''.join(output)

# 給定規(guī)則文本，構(gòu)建規(guī)則字典
def regex_build(code, macros = None, capture = True):
    defined = {}
    if macros is not None:
        for k, v in macros.items():
            defined[k] = v
    line_num = 0
    for line in code.split('\n'):
        line_num += 1
        line = line.strip('\r\n\t ')
        if (not line) or line.startswith('#'):
            continue
        pos = line.find('=')
        if pos < 0:
            raise ValueError('%d: not a valid rule'%line_num)
        head = line[:pos].strip('\r\n\t ')
        body = line[pos + 1:].strip('\r\n\t ')
        if (not head):
            raise ValueError('%d: empty rule name'%line_num)
        elif head[0].isdigit():
            raise ValueError('%d: invalid rule name "%s"'%(line_num, head))
        elif ('<' in head) or ('>' in head):
            raise ValueError('%d: invalid rule name "%s"'%(line_num, head))
        try:
            pattern = regex_expand(defined, body, guarded = not capture)
        except ValueError as e:
            raise ValueError('%d: %s'%(line_num, str(e)))
        try:
            re.compile(pattern)
        except re.error:
            raise ValueError('%d: invalid pattern "%s"'%(line_num, pattern))
        if not capture:
            defined[head] = pattern
        else:
            defined[head] = '(?P<%s>%s)'%(head, pattern)
    return defined

# 定義一套組合規(guī)則
rules = r'''
    protocol = http|https
    login_name = [^:@\r\n\t ]+
    login_pass = [^@\r\n\t ]+
    login = {login_name}(:{login_pass})?
    host = [^:/@\r\n\t ]+
    port = \d+
    optional_port = (?:[:]{port})?
    path = /[^\r\n\t ]*
    url = {protocol}://({login}[@])?{host}{optional_port}{path}?
'''

# 將上面的規(guī)則展開(kāi)成字典
m = regex_build(rules, capture = True)

# 輸出字典內(nèi)容
for k, v in m.items(): 
    print(k, '=', v)

print()

# 用最終規(guī)則 "url" 匹配文本
pattern = m['url']
s = re.match(pattern, 'https://name:pass@www.baidu.com:8080/haha')

# 打印完整匹配
print('matched: "%s"'%s.group(0))
print()

# 按名字打印分組匹配
for name in ('url', 'login_name', 'login_pass', 'host', 'port', 'path'):
    print('subgroup:', name, '=', s.group(name))

完事，主要邏輯 84 行代碼。

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