I'm starting to use Python in the Field Calculator and I just found this out after an hour or so of frustration using rstrip() and rsplit() realized its even easier though not as obvious.
So lets say I wanted to remove the leading character of a 8 digit string in my [UID] field
In VB I'd say:
Right([UID], 7)
In Python I'm saying
!UID![1:]
You may put numbers after the colon [1:4] as well to manipulate the return string lengths and where the string is pulling those lengths from, other than that I don't know but it may help if someone knows the name of this function - if so please comment below?