Python : Files (Reading multiple data record)

Hi There, I am currently working on how to read multiples files in a folder and have been stuck on to write the right code .
My files contains multi lines of numbers and strings seperated by a delimeter[:].
I would like to iterate over each line and split these lines into two parts starting from the first delimeter.
define a function to read files
iterate over each line
Create list 1
As soon as the delimeter line is read
Create list 2
return a tupple (list1 and list2).

All ideas are welcome.Thanks