the same strings, different utf-8 repr values?

[slowness.chen at gmail.com]

I have two files:

test.py:
--------------------------------------------------
# -*- encoding : utf8 -*-
print 'in this file', repr('中文')

# tt.txt is saved as utf8 encoding
f = file('tt.txt')
line1 = f.readline().strip()
print 'another file', repr(line1)
-------------------------------------------------------

tt.txt:
----------------------------------------------------
中文
test
-------------------------------------------------------
run test.py and I get the following output:
in this file '\xe4\xb8\xad\xe6\x96\x87'
another file '\xef\xbb\xbf\xe4\xb8\xad\xe6\x96\x87'

and I cann't encode line1 like:
       line1.decode('utf8').encode('gbk')
get this error:
UnicodeEncodeError: 'gbk' codec can't encode character u'\ufeff' in
position 0:
illegal multibyte sequence

why did I get the different repr values?