Need help to understand the star quantifier (*) output

Question

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?

Asked By: meallhour

||

Source

Answer 1

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+?

Answered By: VOL

Need help to understand the star quantifier (*) output

Question:

Answers: