Python研究

Question

我有一个包含

的字符串变量

string = "123hello456world789"

字符串不包含空格。我想写一个正则表达式，只打印包含(a-z)的单词我尝试了一个简单的正则表达式

pat = "([a-z]+){1,}"
match = re.search(r""+pat,word,re.DEBUG)

匹配对象只包含单词Hello，不匹配单词World。

当使用 re.findall() 时，我可以得到 Hello 和 World。

我的问题是为什么我们不能使用 re.search() 来做到这一点？

如何用 re.search() 做到这一点？

Answer 1

re.search() 在字符串中找到模式一次，documenation :

Scan through string looking for a location where the regular expression pattern produces a match, and return a corresponding MatchObject instance. Return None if no position in the string matches the pattern; note that this is different from finding a zero-length match at some point in the string.

为了匹配每一个的出现，你需要re.findall(), documentation :

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.

示例:

>>> import re
>>> regex = re.compile(r'([a-z]+)', re.I)
>>> # using search we only get the first item.
>>> regex.search("123hello456world789").groups()
('hello',)
>>> # using findall we get every item.
>>> regex.findall("123hello456world789")
['hello', 'world']

---

更新:

由于 your duplicate question ( as discussed at this link ) 我在这里也添加了我的其他答案:

>>> import re
>>> regex = re.compile(r'([a-z][a-z-\']+[a-z])')
>>> regex.findall("HELLO W-O-R-L-D") # this has uppercase
[]  # there are no results here, because the string is uppercase
>>> regex.findall("HELLO W-O-R-L-D".lower()) # lets lowercase
['hello', 'w-o-r-l-d'] # now we have results
>>> regex.findall("123hello456world789")
['hello', 'world']

如您所见，您提供的第一个示例失败的原因是大写，您可以简单地添加 re.IGNORECASE 标志，尽管您提到匹配应该是仅限小写。