How to remove first or last few characters from a string?

I have only ever written a few lines and don´t really understand what I´m doing. So could any one please explain to me why this doesn´t work for "end = 0" and how could I make it work?

Thank you kindly 🙂

start = rs.GetInteger
end = rs.GetInteger
end = -end

objectIDs = rs.GetObjects("Pick some object")

for singleID in objectIDs:
   name = rs.ObjectName(singleID)
   name = name[start:end]
   rs.ObjectName(singleID,name)

… so if the object name is 123456789 and I input 5 and 0 I get 6789.
If I input 0 and 4 I get 12345.
For 2 and 3 I get 3456, etc.

edit:
OK, thank’s to you I think I understand why it doesn´t work and I think I fixed it thus:

start = rs.GetInteger
if start == 0: start = None
end = rs.GetInteger
end = -end
if end == 0: end = None


objectIDs = rs.GetObjects("Pick some object")

for singleID in objectIDs:
   name = rs.ObjectName(singleID)
   name = name[start:end]
   rs.ObjectName(singleID,name)