Correct, my characterization above was wrong (I shouldn't write these up without the interpreter right in front of me). What is wrong with the conversion is:

unicode("", "utf-8") in python 2.x should become either str(b"", "utf-8") or, better, just "" in Python 3.x.  The better version could be done if the codec and value can be represented in the encoding of the output 3.x source code file as is but that optimization is not critical.

In order for str() to take a second arg (the codec) the first cannot be a unicode string already:

>>> str("foo", "utf-8")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: decoding str is not supported