Python 3 renamed the unicode type to str, the old str type has been replaced by bytes.

if isinstance(unicode_or_str, str):
    text = unicode_or_str
    decoded = False
else:
    text = unicode_or_str.decode(encoding)
    decoded = True

You may want to read the Python 3 porting HOWTO for more such details. There is also Lennart Regebro's Porting to Python 3: An in-depth guide, free online.

Last but not least, you could just try to use the 2to3 tool to see how that translates the code for you.

in python 3 strings are unicode by default.

Remove the unicode function, replace by str.

https://docs.python.org/3.0/whatsnew/3.0.html#text-vs-data-instead-of-unicode-vs-8-bit

There's also a little recipe to make the code python 2 & 3 compatible:

try:
    unicode        # check if unicode is defined
except NameError:  # not found: python 3: replace by str
    unicode = str

Like Bakuriu said in his comment, never use a bare except:

Prefer:

except Exception as e:
    print("Problem "+repr(e))
    # the line below requires some HTML normalization or resulting
    # html could be incorrect
    import re
    ne = re.sub("[^\w]"," ",str(e))
    self.browser.append("<font color=red>"+ne+"</font>")

Now you have the real/next exception displayed.