file = open("test.log", "wb")
file.write("."*100 + "\n" + "."*4100 + "\n" + "."*100)
file.close()

file = open ("test.log", "rb")
data = file.read(4096)
data = file.readline()
print "Current fd position:    "+str(file.tell())
seek_back=4100
print "seeking back:           "+str(seek_back)
data = file.seek(-seek_back, 1)
print "fd position after seek: "+str(file.tell())
assert file.tell()==102
print "No errors"