Matching of parentheses in python regular expressions

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M = re. findall ('[0-9] * 4 [0-9] *', '[4]')
It can be matched to 4.
M = re. findall ('([0-9]) * 4 ([0-9]) *', '[4]')
No matching 4.
Why? PS. this is a simplified description. the regular expression I want to use is more complex than this one, so I need to use () to indicate a sequence matching.
In addition, when I put it in notepad ++, both methods can be matched. I don't know why python doesn't work.

Answer:

In the python regular expression, () is used for matching. Therefore, the returned result is ['',''], that is, matching in two. To achieve the original matching effect, there are two solutions to Match 4:

1. the outermost layer is enclosed by braces and becomes m = re. findall ('([0-9]) * 4 ([0-9]) *)', '[4]'), the first element of the returned result is the matching result.
2. remove () and add question mark (?) before brackets? :, To m = re. findall ('(? : \ D) * 4 (? : \ D) * ',' [4] '). The Returned result is the result to be matched.