Question

I am trying to access list element from the token variable, but I keep on getting the error

 print token[0]
IndexError: list index out of range'

When I try to access the element from token list.

The contents of the file rebase file are:

ZraI       3 GAC'GTC        0 !  AatII                            >INV 
;ZrmI      3 AGT'ACT        0 !  ScaI,AssI,BmcAI                   >I

and the code is:

 with open (rebase_file, 'r') as rebase:
     lines = rebase.readlines()
     string  = ''
     for line in lines:
         token = line.split()
         print token[0]

Answer 1

You encountered an empty line:

>>> ''.split()[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range

Simply test for this with if line.strip()::

with open (rebase_file, 'r') as rebase:
    for line in rebase:
        if line.strip():
            token = line.split()
            print token[0]

Note that I loop over the file directly instead of reading it all into memory in one go as well.