[Tutor] long int in list as argument for seek() function

[lmac]

Hi there,
i want to use an long int from an list which i got from my function 
find_lineno().
But i got this error and i don't understand why i can not use this long 
as an argument.
Where do i find a good documentation on errors so that i complete 
understand what
the heck is going on.
Many thanks.

ERROR:
---------------------------------------------------
Traceback (most recent call last):
  File "./extrmails.py", line 42, in ?
    inputfile.seek(0,li)
IOError: [Errno 22] Invalid argument
---------------------------------------------------


CODE-START:
-----------------------------------------------------------------------------

inputfile=open("mails","rt")

# --------------------------------------------------------------------------
def reset_inputfile():
        inputfile.seek(0,0)

# --------------------------------------------------------------------------
def find_lineno(string):
        f = -1
        a = "start"
        found_lines = []
        reset_inputfile()

        while len(a) != 0:
                a = inputfile.readline()
                f = a.find(string)
                if f != -1:
                        found_lines.append(inputfile.tell())

        return found_lines

# --------------------------------------------------------------------------

from_lineno=find_lineno("From:")
subj_lineno=find_lineno("Subject:")

print len(subj_lineno)
print len(from_lineno)

reset_inputfile()

for li in subj_lineno:       
    inputfile.seek(0,li)    <------ ??????? 
    .......
    ......
--------------------------------------------------------------------------
CODE-END