尝试在 python 中使用正则表达式

Question

任何人都可以帮助我理解这段代码片段，来自 http://garethrees.org/2007/05/07/python-challenge/ Level2

>>> import urllib
>>> def get_challenge(s):
...     return urllib.urlopen('http://www.pythonchallenge.com/pc/' + s).read()
...
>>> src = get_challenge('def/ocr.html')
>>> import re
>>> text = re.compile('<!--((?:[^-]+|-[^-]|--[^>])*)-->', re.S).findall(src)[-1]
>>> counts = {}
>>> for c in text: counts[c] = counts.get(c, 0) + 1
>>> counts

http://garethrees.org/2007/05/07/python-challenge/

re.compile('', re.S).findall(src)[-1]为什么我们这里有[-1]有什么用呢？是将其转换为列表吗？ **

Answer 1

它已经是一个列表。如果您有一个列表 myList，myList[-1] returns 该列表中的最后一个元素。

读这个：https://docs.python.org/2/tutorial/introduction.html#lists。

Answer 2

是的。 re.findall() returns 所有匹配的列表。看看 the documentation.

re.findall(pattern, string, flags=0)

Return all non-overlapping matches of pattern in string, as a list of strings. The string is scanned left-to-right, and matches are returned in the order found. If one or more groups are present in the pattern, return a list of groups; this will be a list of tuples if the pattern has more than one group. Empty matches are included in the result unless they touch the beginning of another match.

在结果上调用 [-1] 时，访问列表末尾的第一个元素。

例如；

>>> a = [1,2,3,4,5] >>> a[-1] 5

还有：

>>> re.compile('.*?-').findall('-foo-bar-')[-1] 'bar-'

尝试在 python 中使用正则表达式

trying to regex in python

python

regex

python-3.x

beautifulsoup

urllib