hints:

1. ^ --> matches the start of a string
2. . --> matches any character except a newline
3. \. --> matches . (dot) in a string
4. $ --> matches the end of a string

Why is the testcase failing at hackerrank when it is working fine for me on google colab? regex_pattern = r"(....)+..."

"Your task is to write a regular expression that matches only and exactly strings of form: abc.def.ghi.jkx."

1. It doesn't specify there should only be 4 groups of "xxx.", so I thought "abc.def.ghi.jkl.mno" would match
2. It isn't clear the last dot next to x is included in the string or not.

"^.{3}..{3}..{3}..{3}$"

I think we have a wrong test cases here. pattern /(.{3}.){3}.{3}/ with string 1123.456.abc.def must return false. How can it return true In PHP and JavaScript it works wrong, but if I select python it works but failed in another cases.