Ibuava,
The result of this operation will be a string. Numeric values do not have "dots" in them. Within python, as a string, you can use a simple string slice and append function, such as:
oldNum = str(1234567890)
newNum = oldNum[:2] + "." + oldNum[2:4] + "." + oldNum[4:7] +"." + oldNum[7:]
newNum
'12.34.567.890'
This assumes the oldNum is 10 characters in each entry.
If it is not always10 characters, work from the end of the string value to the front, instead.
If you are trying to do something else, please provide more information so you can get a targeted response to your question.
Regards,
Jim