贪婪和懒惰量词。使用 HTML 标签进行测试

Question

输入是<p>The very <em>first</em> task is to find the beginning of a paragraph.</p><p>Then you have to find the end of the paragraph</p>预期的第一个输出是（因为我使用贪婪量词）<p>The very <em>first</em> task is to find the beginning of a paragraph.</p><p>Then you have to find the end of the paragraph</p>用于贪婪的代码如下text = '''<p>The very <em>first</em> task is to find the beginning of a paragraph.</p><p>Then you have to find the end of the paragraph</p>'''pattern=re.compile(r'\<p\>.*\<\/p\>')data1=pattern.match(text,re.MULTILINE)print('data1:- ',data1,'\n')预期的第二个输出是（因为我使用的是惰性量词）<p>The very <em>first</em> task is to find the beginning of a paragraph.</p>用于懒惰的代码如下text = '''<p>The very <em>first</em> task is to find the beginning of a paragraph.</p><p>Then you have to find the end of the paragraph</p>'''#pattern=re.compile(r'\<p\>.*?\<\/p\>')pattern=re.compile(r'<p>.*?</p>')data1=pattern.match(text,re.MULTILINE)print('data1:- ',data1,'\n')我得到的实际输出都是 None

Answer 1

你有几个问题。首先，使用 时Pattern.match，第二个和第三个参数是位置参数，而不是标志。需要将标志指定为re.compile。其次，您应该使用re.DOTALL来.匹配换行符，而不是re.MULTILINE. 最后 -match坚持匹配发生在字符串的开头（在您的情况下是换行符），因此它不会匹配。您可能想改用Pattern.search。这适用于您的示例输入：

pattern=re.compile(r'<p>.*</p>', re.DOTALL)

data1=pattern.search(text)

print('data1:- ',data1.group(0),'\n')

输出：

data1:-  <p>

The very <em>first</em> task is to find the beginning of a paragraph.

</p>

<p>

Then you have to find the end of the paragraph

</p> 

单场比赛：

pattern=re.compile(r'<p>.*?</p>', re.DOTALL)

data1=pattern.search(text)

print('data1:- ',data1.group(0),'\n')

输出：

data1:-  <p>

The very <em>first</em> task is to find the beginning of a paragraph.

</p> 

另请注意/， ,<和>在正则表达式中没有特殊含义，不需要转义。我已经在上面的代码中删除了它。