an erro happened when i use this code

[zhanshenzonghengtianxia]

could you give an example about the usage? i do not know how to use it ,when a use the pygsf.py, an erro happened :
Traceback (most recent call last):
File "/home/wangjie/Downloads/pygsf-master/tryread.py", line 68, in
numberofbytes, recordidentifier, datagram = r.readDatagram()
File "/home/wangjie/Downloads/pygsf-master/pygsf.py", line 847, in readDatagram
dg = UNKNOWN_RECORD(self.fileptr, numberofbytes, recordidentifier, hdrlen)
File "/home/wangjie/Downloads/pygsf-master/pygsf.py", line 172, in init
self.fileptr.seek(numbytes, 1) # set the file ptr to the end of the record
ValueError: seek out of range