如何从python中的正则表达式匹配返回一个字符串？

Question

我正在使用python脚本在文本文件中运行行.我想img在文本文档中搜索标记并将标记作为文本返回.

当我运行正则表达式时,re.match(line)它返回一个 _sre.SRE_MATCH对象.如何让它返回一个字符串？

import sys
import string
import re

f = open("sample.txt", 'r' )
l = open('writetest.txt', 'w')

count = 1

for line in f:
    line = line.rstrip()
    imgtag  = re.match(r'<img.*?>',line)
    print("yo it's a {}".format(imgtag))

运行时打印:

yo it's a None
yo it's a None
yo it's a None
yo it's a <_sre.SRE_Match object at 0x7fd4ea90e578>
yo it's a None
yo it's a <_sre.SRE_Match object at 0x7fd4ea90e578>
yo it's a None
yo it's a <_sre.SRE_Match object at 0x7fd4ea90e578>
yo it's a <_sre.SRE_Match object at 0x7fd4ea90e5e0>
yo it's a None
yo it's a None

Answer 1

你应该用re.MatchObject.group(0).喜欢

imtag = re.match(r'<img.*?>', line).group(0)

编辑:

你也可能会做更好的事情

imgtag  = re.match(r'<img.*?>',line)
if imtag:
    print("yo it's a {}".format(imgtag.group(0)))

消除所有的Nones.

Answer 2

imgtag.group(0)或imgtag.group()。这将整个匹配项作为字符串返回。你也没有捕捉任何其他东西。

http://docs.python.org/release/2.5.2/lib/match-objects.html

Answer 3

请注意，re.match(pattern, string, flags=0)仅返回字符串开头的匹配项。如果要在字符串中的任何位置找到匹配项，请re.search(pattern, string, flags=0)改用 ( https://docs.python.org/3/library/re.html )。这将扫描字符串并返回第一个匹配对象。然后您可以match_object.group(0)按照人们的建议提取匹配的字符串。

Answer 4

考虑到img我可能会推荐几个标签re.findall:

import re

with open("sample.txt", 'r') as f_in, open('writetest.txt', 'w') as f_out:
    for line in f_in:
        for img in re.findall('<img[^>]+>', line):
            print >> f_out, "yo it's a {}".format(img)