* Zope API changes:
  + publish():
    - stdin is now BytesIO rather than StringIO.
    - Returned value of a script is passed to str() in python2, not in python3 anymore.
  + HTTPResponse `body` property is now bytes().
  + OFS.Image.File file parameter is bytes().
  + zope.interface implements() is now @implementer decorator.
  + Python standard logging module recommended instead of zLOG.
* Python3 API changes:
  + builtin reduce() was removed.
  + urlnorm is now available.
  + Use BytesIO rather than StringIO to follow py3 API.
  + hmac.new() requires digestmod argument from Python 3.8.
  + Use six.moves library to handle moved objects from py2 to py3.
  + `modernize -f xrange_six` then slightly adjusted manually to just use range
     where it does not make a significant difference (for example in test).
  + base64.b64encode() now expects bytes().
  + UserDict() interface changed:
    - New parameter in update() and pop().
    - `failobj` setdefault parameter renamed to `default`.
  + ensure_list() on dict.{values,items}() and list(dict) for dict.keys() when
    we really need a list and not an iterable (Python3).
  + Make dict iteration works on both version of Python.
    - Use six.iter{items,values,keys}().
    - has_key() has been removed.
    - Make sure that dict.{items,values,keys}() returns a real list when
    modified (ensure_list()).
  + Comparisons between int and NoneType raises TypeError.
    + BTrees key must be str() not int() (_getOb()).
  + No more unbound methods in python3 so use six.get_unbound_function().
  + Exceptions:
    - No longer behave as sequences. Using `args` attribute instead.
    - When an exception has been assigned using `as target`, it is cleared at
      the end of the except clause.
  + file: py2 was returning `str` upon reading, now it returns text strings.
    Also, opening mode is text strings by default.
  + Data strings are bytes().
    - Replace str() by bytes().
  + iterators no longer have next() method, instead there is next() builtin.
  + New ConnectionError exception so rename existing one to not clash.
  + Integer division is now with //.
  + __nonzero__ is now __bool__.
  + apply() does not exist anymore.
  + Deprecated threading.Thread isAlive() has been removed.
  + im_func replaced by __func__.
  + Use six.with_metaclass() to define metaclass in a cross-compatible way with py2 and py3.
  + Only test method can be marked as expectedFailure(), not assert statement anymore.
  + os.path.walk() removed.
  + HTMLParser never fails: no strict mode nor HTMLParseError anymore (Python #15114).
  + Unpickler.find_global() is now Unpickler.find_class().
Co-Authored-by: Kazuhiko SHIOZAKI <kazuhiko@nexedi.com>
Co-Authored-by: Arnaud Fontaine <arnaud.fontaine@nexedi.com>
Co-Authored-by: Carlos Ramos Carreño <carlos.ramos@nexedi.com>
Co-Authored-by: Emmeline Vouriot <emmeline.vouriot@nexedi.com>