如何使用Python中的正则表达式处理html文件
使用Python中的正则表达式处理html文件
finditer方法是一种全匹配方法。您可能已经使用了findall方法,它返回多个匹配字符串的列表。finditer返回一个迭代器顺序地为多个匹配中的每一个生成匹配对象。在下面的代码中,这些匹配对象被访问(通过for循环),因此可以打印组1。
您的任务是编写Python RE来识别HTML文本文件中的某些模式。将代码添加到STARTER脚本为这些模式编译RE(将它们分配给有意义的变量名称),并将这些RE应用于文件的每一行,打印出找到的匹配项。
1.编写识别HTML标签的模式,然后将其打印为“TAG:TAG string”(例如“TAG:b”代表标签)。为了简单起见,假设左括号和右括号每个标记的(<,>)将始终出现在同一行文本中。第一次尝试可能使regex“<.*>”其中“.”是与任何字符匹配的预定义字符类符号。尝试找出这一点,找出为什么这不是一个好的解决方案。编写一个更好的解决方案,解决这个问题
2.修改代码,使其区分开头和结尾标记(例如p与/p)打印OPENTAG和CLOSETAG
import sys, re #------------------------------ testRE = re.compile('(logic|sicstus)', re.I) testI = re.compile('<[A-Za-z]>', re.I) testO = re.compile('<[^/](\S*?)[^>]*>') testC = re.compile('</(\S*?)[^>]*>') with open('RGX_DATA.html') as infs: linenum = 0 for line in infs: linenum += 1 if line.strip() == '': continue print(' ', '-' * 100, '[%d]' % linenum, '\n TEXT:', line, end='') m = testRE.search(line) if m: print('** TEST-RE:', m.group(1)) mm = testRE.finditer(line) for m in mm: print('** TEST-RE:', m.group(1)) index= testI.finditer(line) for i in index: print('Tag:',i.group().replace('<', '').replace('>', '')) open1= testO.finditer(line) for m in open1: print('opening:',m.group().replace('<', '').replace('>', '')) close1= testC.finditer(line) for n in close1: print('closing:',n.group().replace('<', '').replace('>', ''))
请注意,有些HTML标签有参数,例如:
<table border=1 cellspacing=0 cellpadding=8>
确保打开标记的模式适用于带参数和不带参数的标记,即成功找到并打印标签标签。现在扩展您的代码,以便打印两个打开的标签标签和参数,例如:
OPENTAG: table
PARAM: border=1
PARAM: cellspacing=0
PARAM: cellpadding=8
open1= testO.finditer(line) for m in open1: #print('opening:',m.group().replace('<', '').replace('>', '')) firstm= m.group().replace('<', '').replace('>', '').split() num = 0 for otherm in firstm: if num == 0: print('opening:',otherm) else: print('pram:',otherm) num+= 1
在正则表达式中,可以使用反向引用来指示匹配早期部分的子字符串,应再次出现正则表达式的。格式为\N(其中N为正整数),并返回到第N个匹配的文本正则表达式组。例如,正则表达式,如:r" (\w+) \1 仅当与组(\w+)完全匹配的字符串再次出现时才匹配 backref\1出现的位置。这可能与字符串“踢”匹配.例如,“the”出现两次。使用反向引用编写一个模式,当一行包含成对的open和关闭标签,例如在粗体中.
考虑到我们可能想要创建一个执行HTML剥离的脚本,即一个HTML文件,并返回一个纯文本文件,所有HTML标记都已从中删除出来这里我们不打算这样做,而是考虑一个更简单的例子,即删除我们在输入数据文件的任何行中找到的HTML标记。
你应该能够让您已经定义的RE识别HTML标签这样做,将生成的文本打印到屏幕上为STRIPPED:。。
import sys, re #------------------------------ # PART 1: # Key thing is to avoid matching strings that include # multiple tags, e.g. treating '<p><b>' as a single # tag. Can do this in several ways. Firstly, use # non-greedy matching, so get shortest possible match # including the two angle brackets: tag = re.compile('</?(.*?)>') # The above treats the '/' of a close tag as a separate # optional component - so that this doesn't turn up as # part of the match '.group(1)', which is meant to return # the tag label. # Following alternative solution uses a negated character # class to explicitly prevent this including '>': tag = re.compile('</?([^>]+)>') # Finally, following version separates finding the tag # label string from any (optional) parameters that might # also appear before the close angle bracket: tag = re.compile(r'</?(\w+\b)([^>]+)?>') # Note that use of '\b' (as word boundary anchor) here means # we must mark the regex string as a 'raw' string (r'..'). #------------------------------ # PART 2: # Following closeTag definition requires first first char # after the open angle bracket to be '/', while openTag # definition excludes this by requiring first char to be # a 'word char' (\w): openTag = re.compile(r'<(\w[^>]*)>') closeTag = re.compile(r'</([^>]*)>') # Following revised definitions are more carefully stated # for correct extraction of tag label (separately from # any parameters: openTag = re.compile(r'<(\w+\b)([^>]+)?>') closeTag = re.compile(r'</(\w+\b)\s*>') #------------------------------ # PART 3: # Above openTag definition will already get the string # encompassing any parameters, and return it as # m.group(2), i.e. defn: openTag = re.compile(r'<(\w+\b)([^>]+)?>') # If assume that parameters are continuous non-whitespace # chars separated by whitespace chars, then we can divide # them up using split - and that's how we handle them # here. (In reality, parameter strings can be a lot more # messy than this, but we won't try to deal with that.) #------------------------------ # PART 4: openCloseTagPair = re.compile(r'<(\w+\b)([^>]+)?>(.*?)</\1\s*>') # Note use of non-greedy matching for the text falling # *between* the open/close tag pair - to avoid false # results where have two similar tag pairs on same line. #------------------------------ # PART 5: URLS # This is quite tricky. The URL expressions in the file # are of two kinds, of which the first is a string # between double quotes ("..") which may include # whitespace. For this case we might have a regex: url = re.compile('href=("[^">]+")', re.I) # The second case does not have quotes, and does not # allow whitespace, consisting of a continuous sequence # of non-whitespace material (that ends when you reach a # space or close bracket '>'). This might be: url = re.compile('href=([^">\s]+)', re.I) # We can combine these two cases as follows, and still # get the expression back as group(1): url = re.compile(r'href=("[^">]+"|[^">\s]+)', re.I) # Note that I've done nothing here to exclude 'mailto:' # links as being accepted as URLS. #------------------------------ with open('RGX_DATA.html') as infs: linenum = 0 for line in infs: linenum += 1 if line.strip() == '': continue print(' ', '-' * 100, '[%d]' % linenum, '\n TEXT:', line, end='') # PART 1: find HTML tags # (The following uses 'finditer' to find ALL matches # within the line) mm = tag.finditer(line) for m in mm: print('** TAG:', m.group(1), ' + [%s]' % m.group(2)) # PART 2,3: find open/close tags (+ params of open tags) mm = openTag.finditer(line) for m in mm: print('** OPENTAG:', m.group(1)) if m.group(2): for param in m.group(2).split(): print(' PARAM:', param) mm = closeTag.finditer(line) for m in mm: print('** CLOSETAG:', m.group(1)) # PART 4: find open/close tag pairs appearing on same line mm = openCloseTagPair.finditer(line) for m in mm: print("** PAIR [%s]: \"%s\"" % (m.group(1), m.group(3))) # PART 5: find URLs: mm = url.finditer(line) for m in mm: print('** URL:', m.group(1)) # PART 6: Strip out HTML tags (note that .sub will do all # possible substitutions, unless number is limited by count # keyword arg - which is fortunately what we want here) stripped = tag.sub('', line) print('** STRIPPED:', stripped, end = '')
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