import unittest

from io import StringIO

ENCODING = 'utf-8'

S0 = 'hello world, Umlauts: äöüßÄÖÜ, Chinese: 四是四，十是十，十四是十四，四十是四十，四十四隻不識字之石獅子是死的'
S0_BYTES = 'fe fi foe fam'.encode(ENCODING)

#print("###", StringIO, "###")

class TestStringIO(unittest.TestCase):

    def test_001_text(self):
        # If we throw unicode into the StringIO buffer, we'll
        # get unicode out of it.
        self.assertEqual(type(S0), str)
        buf = StringIO()
        print(S0, file=buf, end="")
        s1 = buf.getvalue()
        self.assertEqual(type(S0), type(s1))
        self.assertEqual(S0, s1)
        self.assertEqual(type(s1), str)

    def test_002_bytes(self):
        buf = StringIO()
        print(S0_BYTES, file=buf, end="")
        s1 = buf.getvalue()

        # In Python 3 StringIO *ALWAYS* returns str (=text=unicode) !
        # Even if we originally write bytes into the buffer, the value
        # we get out of it has type str!

        # Input is bytes
        self.assertEqual(type(S0_BYTES), bytes)
        # Output is NOT bytes...
        self.assertNotEqual(type(S0_BYTES), type(s1))
        self.assertNotEqual(type(s1), bytes)
        # ...but str!
        self.assertEqual(type(s1), str)
        # So the contents are not equal!
        self.assertNotEqual(S0_BYTES, s1)
        # StringIO coerced bytes into str:
        # b'xyz' ---> "b'xyz'"
        self.assertEqual(str(S0_BYTES), s1)
        # See, the type info is literally present in the output str!
        self.assertEqual("b'" + str(S0_BYTES, encoding=ENCODING) + "'", s1)
        # Coercion is NOT decoding!
        self.assertNotEqual(S0_BYTES.decode(ENCODING), s1)
        self.assertNotEqual(str(S0_BYTES, encoding=ENCODING), s1)
        # These are the same
        self.assertEqual(S0_BYTES.decode(ENCODING),
            str(S0_BYTES, encoding=ENCODING))
        # Additional note:
        # If we do not specify an encoding when we create a StringIO
        # buffer, Python 3 automatically uses the locale's preferred
        # encoding: locale.getpreferredencoding()
        # Cf. http://docs.python.org/release/3.0.1/library/io.html#io.TextIOWrapper
        # In my case this is the same encoding as the encoding of this source file,
        # namely UTF-8. If on your system both encodings are different, you may
        # encounter other results than the above.
        #
        # In Python 3.2 the signature of StringIO() has changed. It is no more
        # possible to specify an encoding here.