正则表达式只捕获重复组的最后一次出现

Question

I am trying to capture multiple "<attribute> = <value>" pairs with a Python regular expression from a string like this:

  some(code) ' <tag attrib1="some_value" attrib2="value2"                   en=""/>

The regular expression '\\s*<tag(?:\\s*(\\w+)\\s*=\\"(.*?)\\")* is intended to match those pairs multiple times, ie return something like

"attrib1", "some_value", "attrib2", "value2", "en", ""

but it only captures the last occurence:

>>> import re
>>> re.search("'\s*<tag(?:\s*(\w+)\s*=\"(.*?)\")*", '  some(code) \' <tag attrib1="some_value" attrib2="value2"                   en=""/>').groups()
('en', '')

Focusing on <attrib>="<value>" works:

>>> re.findall("(?:\s*(\w+)\s*=\"(.*?)\")", '  some(code) \' <tag attrib1="some_value" attrib2="value2"                   en=""/>')
[('attrib1', 'some_value'), ('attrib2', 'value2'), ('en', '')]

so a pragmatic solution might be to test "<tag" in string before running this regular expression, but..

Why does the original regex only capture the last occurence and what needs to be changed to make it work as intended?

Answer 1

This is just how regex works : you defined one capturing group, so there is only one capturing group. When it first captures something, and then captures an other thing, the first captured item is replaced.That's why you only get the last captured one.
There is no solution for that that I am aware of...

Answer 2

Unfortunately this is not possible with python's re module. But regex provides captures and capturesdict functions for that:

>>> m = regex.match(r"(?:(?P<word>\w+) (?P<digits>\d+)\n)+", "one 1\ntwo 2\nthree 3\n")
>>> m.groupdict()
{'word': 'three', 'digits': '3'}
>>> m.captures("word")
['one', 'two', 'three']
>>> m.captures("digits")
['1', '2', '3']
>>> m.capturesdict()
{'word': ['one', 'two', 'three'], 'digits': ['1', '2', '3']}

Answer 3

From the documentation search will return only one occurrence. The findAll method returns all occurrences in the list. That is what you need to use, like in your second example.