Splitting up the digits in python using regex

Question

I am trying to learn regex in python. I came across the "split" function where we have to give pattern and the string. I could understand the below output:

a = '123456789'
b = re.split("(4)", a)
print(b)
['123', '4', '56789']

But I could not understand this below output. Why is "3" is not printing out in the output? Can someone please explain?

a = '123456789'
b = re.split("\d(4)", a)
print(b)
['12', '4', '56789']

Answer 1

You have told it to split at \\d(4) , so it will find a part of your string that matches \\d(4) . That part is 34 , 3 for \\d and 4 for (4) .

If you split the string there, you get 12 in front of it and 56789 after it.

For the middle part, you have only put the 4 into a capturing group: (4) , so only the 4 will be captured, not the 3 .

Things to try next for a better understanding:

• use \\d4 as the delimiter, without any capturing group
• use (\\d4) as the delimiter, including the 3 in the capturing group

Solutions available at https://ideone.com/3yCKGF