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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def byte_str(s="", encoding="utf-8", input_encoding="utf-8", errors="strict"):
 """ Returns a byte string version of 's', encoded as specified in 'encoding'. Accepts str & unicode objects, interpreting non-unicode strings as byte strings encoded using the given input encoding. """

    assert isinstance(s, basestring)
    if isinstance(s, unicode):
        return s.encode(encoding, errors)
    if s and encoding != input_encoding:
        return s.decode(input_encoding, errors).encode(encoding, errors)
    return s