Need help to understand the star quantifier (*) output-CodePudding

I am able to understand output of the below command:

import re
text = "streets2345"
pattern = r"\d "
match = re.search(pattern, text)
print(match.group(0))

Output: 2345

However, I am not able to understand why the below code is returning null.

import re
text = "streets2345"
pattern = r"\d*"
match = re.search(pattern, text)
print(match.group(0))

Output: null

Here, the first character s of the text matches the pattern \d*.

So, why the output is not s instead of null?

CodePudding user response：

\d* will match 0 or more digits. 's' is not a digit, but it will match the position before the 's' as there's 0 digits. Thus the first group will be null (empty). In fact, the first 7 groups will be null because of the same reason, the last one being the position before the last 's' in "streets". The 8th group (index 7) will be "2345".

\d will match 1 or more digits. As you don't have a digit before the first 's' (again, there's 0 digits), you won't get a match in there in this case.

If \d* didn't match the empty 0-digit positions before each letter, what would be the difference of \d* and \d ?