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 = '')