Python正则表达式 - re.search（）vs re.findall（）

For school I'm supposed to write a Python RE script that extracts IP addresses. The regular expression I'm using seems to work with re.search() but not with re.findall().

对于学校，我应该编写一个提取IP地址的Python RE脚本。我正在使用的正则表达式似乎与re.search（）一起使用，但不与re.findall（）一起使用。

exp = "(\d{1,3}\.){3}\d{1,3}"
ip = "blah blah 192.168.0.185 blah blah"
match = re.search(exp, ip)
print match.group()

The match for that is always 192.168.0.185, but its different when I do re.findall()

它的匹配总是192.168.0.185，但当我执行re.findall（）时它的不同

exp = "(\d{1,3}\.){3}\d{1,3}"
ip = "blah blah 192.168.0.185 blah blah"
matches = re.findall(exp, ip)
print matches[0]

0.

I'm wondering why re.findall() yields 0. when re.search() yields 192.168.0.185, since I'm using the same expression for both functions.

我想知道为什么re.findall（）得到0.当re.search（）产生192.168.0.185，因为我对两个函数使用相同的表达式。

And what can I do to make it so re.findall() will actually follow the expression correctly? Or am I making some kind of mistake?

我能做些什么才能使它成为re.findall（）实际上会正确地遵循表达式？还是我犯了某种错误？

2 个解决方案

#1

findall returns a list of matches, and from the documentation:

findall返回匹配列表，并从文档中：

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.

如果模式中存在一个或多个组，则返回组列表;如果模式有多个组，这将是一个元组列表。

So, your previous expression had one group that matched 3 times in the string where the last match was 0.

因此，您之前的表达式有一个组在最后一个匹配为0的字符串中匹配3次。

To fix your problem use: exp = "(?:\d{1,3}\.){3}\d{1,3}"; by using the non-grouping version, there is no returned groups so the match is returned in both cases.

要解决您的问题，请使用：exp =“（？：\ d {1,3} \。）{3} \ d {1,3}”;通过使用非分组版本，没有返回的组，因此在两种情况下都返回匹配。

#2

You're only capturing the 0 in that regex, as it'll be the last one that's caught.

你只是捕获了那个正则表达式中的0，因为它将是最后一个被捕获的。

Change the expression to capture the entire IP, and the repeated part to be a non-capturing group:

更改表达式以捕获整个IP，并将重复的部分更改为非捕获组：

In [2]: ip = "blah blah 192.168.0.185 blah blah"

In [3]: exp = "((?:\d{1,3}\.){3}\d{1,3})"

In [4]: m = re.findall(exp, ip)

In [5]: m
Out[5]: ['192.168.0.185']

In [6]:

And if it helps to explain the regex:

如果它有助于解释正则表达式：

In [6]: re.compile(exp, re.DEBUG)
subpattern 1
  max_repeat 3 3
    subpattern None
      max_repeat 1 3
        in
          category category_digit
      literal 46
  max_repeat 1 3
    in
      category category_digit

This explains the subpatterns. Subpattern 1 is what gets captured by findall.

这解释了子模式。子模式1是findall捕获的内容。

#1