如何使用Python中的正則表達式處理html文件
使用Python中的正則表達式處理html文件
finditer方法是一種全匹配方法。您可能已經(jīng)使用了findall方法,它返回多個匹配字符串的列表。finditer返回一個迭代器順序地為多個匹配中的每一個生成匹配對象。在下面的代碼中,這些匹配對象被訪問(通過for循環(huán)),因此可以打印組1。
您的任務是編寫Python RE來識別HTML文本文件中的某些模式。將代碼添加到STARTER腳本為這些模式編譯RE(將它們分配給有意義的變量名稱),并將這些RE應用于文件的每一行,打印出找到的匹配項。
1.編寫識別HTML標簽的模式,然后將其打印為“TAG:TAG string”(例如“TAG:b”代表標簽)。為了簡單起見,假設左括號和右括號每個標記的(<,>)將始終出現(xiàn)在同一行文本中。第一次嘗試可能使regex“<.*>”其中“.”是與任何字符匹配的預定義字符類符號。嘗試找出這一點,找出為什么這不是一個好的解決方案。編寫一個更好的解決方案,解決這個問題
2.修改代碼,使其區(qū)分開頭和結尾標記(例如p與/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('>', ''))請注意,有些HTML標簽有參數(shù),例如:
<table border=1 cellspacing=0 cellpadding=8>
確保打開標記的模式適用于帶參數(shù)和不帶參數(shù)的標記,即成功找到并打印標簽標簽?,F(xiàn)在擴展您的代碼,以便打印兩個打開的標簽標簽和參數(shù),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
在正則表達式中,可以使用反向引用來指示匹配早期部分的子字符串,應再次出現(xiàn)正則表達式的。格式為\N(其中N為正整數(shù)),并返回到第N個匹配的文本正則表達式組。例如,正則表達式,如:r" (\w+) \1 僅當與組(\w+)完全匹配的字符串再次出現(xiàn)時才匹配 backref\1出現(xiàn)的位置。這可能與字符串“踢”匹配.例如,“the”出現(xiàn)兩次。使用反向引用編寫一個模式,當一行包含成對的open和關閉標簽,例如在粗體中.
考慮到我們可能想要創(chuàng)建一個執(zhí)行HTML剝離的腳本,即一個HTML文件,并返回一個純文本文件,所有HTML標記都已從中刪除出來這里我們不打算這樣做,而是考慮一個更簡單的例子,即刪除我們在輸入數(shù)據(jù)文件的任何行中找到的HTML標記。
你應該能夠讓您已經(jīng)定義的RE識別HTML標簽這樣做,將生成的文本打印到屏幕上為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 = '')
總結
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