difference between two regular expressions: [abc]+ and ([abc])+

Question

In [29]: re.findall(\"([abc])+\",\"abc\")
Out[29]: [\'c\']

In [30]: re.findall(\"[abc]+\",\"abc\")
Out[30]: [\'abc\']

Confused by the grouped one.

Answer 1

Here's the way I would think about it. ([abc])+ is attempting to repeat a captured group. When you use "+" after the capture group, it doesn't mean you are going to get two captured groups. What ends up happening, at least for Python's regex and most implementations, is that the "+" forces iteration until the capture group only contains the last match.

If you want to capture a repeated expression, you need to reverse the ordering of "(...)" and "+", e.g. instead of ([abc])+ use ([abc]+).