gistfile1.txt

$ cat test.py 
from cStringIO import StringIO
expected = 'a'
result = StringIO('a').read()
assert result is expected
expected = 'abc'
result = StringIO('abc').read()
assert result is expected, "%s is not %s" % (repr(result), repr(expected))


$ python test.py 
Traceback (most recent call last):
  File "test.py", line 7, in <module>
    assert result is expected, "%s is not %s" % (repr(result), repr(expected))
AssertionError: 'abc' is not 'abc'
clayg@rosco:~$