Änderungen Python 2.x --> 3.x               (C) 2014-2020 T.Birnthaler OSTC GmbH
=============================

Aktivieren von Eigenschaften neuerer Python-Versionen (z.B. Python 3) in
älteren Python-Versionen (z.B. Python2):

  import __future__                        # Alle Eigenschaften
  from __future__ import *                 # FEHLER!
                                           # STD  PEP (Standard ab Version N.M)
  from __future__ import annotations       # 4.0  563 Type annotation
  from __future__ import generator_stop    # 3.7  479 Generator stop
  from __future__ import unicode_literals  # 3.0 3112 Unicode literals in Python 3000
  from __future__ import print_function    # 3.0 3105 Make "print" a function
  from __future__ import with_statement    # 2.6  343 The "with" statement
  from __future__ import absolute_import   # 3.0  328 Import: multi-line + absolute/Relative
  from __future__ import division          # 3.0  238 Changing division operator
  from __future__ import generators        # 2.3  255 Simple generators
  from __future__ import nested_scopes     # 2.2  227 Statically nested scopes
  from __future__ import all_feature_names # ?.? TODO
  from __future__ import barry_as_FLUFL    # 3.9 TODO Easteregg (<> statt !=)

Die __future__-Imports MÜSSEN am Anfang des Quellcodes als 1. Anweisung stehen
(da sie die Verhaltensweise des Python-Interpreters verändern).

Ein kleines "Easteregg" ist auch versteckt (Blockbildung per geschweifte
Klammern {...} wird sicher nie implementiert):

  from __future__ import braces            # --> SyntaxError: not a chance !!!

Unterschiede zwischen Python 2.x und Python 3.x:

  +-------------------------------+------------------------------+
  |         Python 2.x            |          Python 3.x          |
  +-------------------------------+------------------------------+
  | "äöü"            (Bytestring) | b"abc"          (Bytestring) | String
  | u"äöü"    (Unicode erzwingen) | "äöü"          (Unicode Std) | String
  | unicode(VAR)        (Unicode) | str(VAR)       (Unicode Std) | Typ
  | unicode                       | str                          | Typ
  | basestring                    | str                          | Typ
  +-------------------------------+------------------------------+
  | VAR = raw_input(PROMPT)       | VAR = input(PROMPT)          | Direkt lesen
  | VAR = input(PROMPT)           | VAR = eval(input(PROMPT))    | Interpretiert
  +-------------------------------+------------------------------+
  | print ..., ...    (Statement) | print(..., ...)   (Funktion) | Ausgabe
  | print >> sys.stderr ...       | print(..., file=sys.stderr)  | Std: sys.stdout
  | print ...,                    | print(..., end="")           | Std: "\n" (newline)
  | print ... + ...               | print(..., ..., sep="")      | Std: " " (separator)
  | ?                             | print(..., flush="False")    | Nicht puffern
  | "...%d..." % (V1, ...)        | "...{:d}...".format(V1, ...) | Formatieren
  | `...`             (Backticks) | repr(...)                    | Datenrepräsentation
  +-------------------------------+------------------------------+
  | long        2147483648L       | int       2147483648         | Typ
  | 0123                          | 0o123     (oktal)            | Num. Konstante
  |                               | 0b123     (binär)            |  "       "
  | sys.maxint                    | sys.maxsize                  |  "       "
  | 12345L      (long-Zahl)       | 12345     (beliebig lang)    | Typ
  | 5   / 4     (Ganzahldivision) | 5  // 4   (Ganzzahldivision) | Division
  | ---                           | 5   / 4   (Fliesskommadiv.)  |    "
  | 5.0 / 4     (Fliesskommadiv.) | 5.0 / 4   (Fliesskommadiv.)  |    "
  | 5   / 4.0   (Fliesskommadiv.) | 5   / 4.0 (Fliesskommadiv.)  |    "
  | 5.0 / 4.0   (Fliesskommadiv.) | 5.0 / 4.0 (Fliesskommadiv.)  |    "
  | !=  <>                        | !=                           | Ungleich
  +-------------------------------+------------------------------+
  | int                           | bool                         | Typ Boolean
  | 1                             | True                         | Wert "wahr"
  | 0                             | False                        | Wert "falsch"
  +-------------------------------+------------------------------+
  | xrange()                      | range()                      | Umbenennung
  | os.getcwdu()                  | os.getcwd()                  |      "
  | import Tkinter                | import tkinter               |      "
  | intern()                      | sys.intern()                 |      "
  | for X in FILE.xreadlines():   | for X in FILE:               |      "
  +-------------------------------+------------------------------+
  | L = list(SEQ); L.sort()       | L = sorted(SEQ)              | Sortieren
  +-------------------------------+------------------------------+
  | DICT.has_key(KEY)             | KEY in DICT                  | Dictionary
  | DICT.iteritems()              | DICT.items()                 |      "
  |     .iterkeys()               |     .keys()                  |      "
  |     .itervalues()             |     .values()                |      "
  |     .viewitems()              |     .items()                 |      "
  |     .viewkeys()               |     .keys()                  |      "
  |     .viewvalues()             |     .values()                |      "
  +-------------------------------+------------------------------+
  | type(X) == CLASS              | isinstance(X, CLASS)         | Typvergleich
  | type(X) is CLASS              | isinstance(X, CLASS)         |      "
  +-------------------------------+------------------------------+
  | except X, T                   | except X as T                | Ausnahmebehandlung
  | raise Exception, "String"     | raise Exception("String")    |      "
  | raise Exc, "Str", Traceback   | raise E(S).with_traceback(T) |      "
  | StandardError                 | Exception                    |      "
  +-------------------------------+------------------------------+
  | exec CODE         (Statement) | exec(CODE)        (Funktion) |
  | execfile(FILE)                | with open(FILE) as fh:       |
  |                               |     exec(fh.read())          |
  | sys.exc_value/type/traceback  | sys.exc_info()    (-> Tupel) | exc=Exception
  +-------------------------------+------------------------------+


Konvertierungs-Programm 2to3 --help
-----------------------------------
Usage: 2to3 [options] file|dir ...

Options:
  -h, --help            Show this help message and exit
  -d, --doctests_only   Fix up doctests only
  -f FIX, --fix=FIX     Each FIX specifies a transformation; default: all
  -j PROCESSES, --processes=PROCESSES
                        Run 2to3 concurrently
  -x NOFIX, --nofix=NOFIX
                        Prevent a transformation from being run
  -l, --list-fixes      List available transformations
  -p, --print-function  Modify the grammar so that print() is a function
  -v, --verbose         More verbose logging
  --no-diffs            Don't show diffs of the refactoring
  -w, --write           Write back modified files
  -n, --nobackups       Don't write backups for modified files
  -o OUTPUT_DIR, --output-dir=OUTPUT_DIR
                        Put output files in this directory instead of
                        overwriting the input files.  Requires -n.
  -W, --write-unchanged-files
                        Also write files even if no changes were required
                        (useful with --output-dir); implies -w.
  --add-suffix=ADD_SUFFIX
                        Append this string to all output filenames. Requires
                        -n if non-empty.  ex: --add-suffix='3' will generate
                        .py3 files.


Korrekturen von 2to3 --list-fixes
---------------------------------
Available transformations for the -f/--fix option:

  apply
  basestring
  buffer
  callable
  dict
  except
  exec
  execfile
  exitfunc
  filter
  funcattrs
  future
  getcwdu
  has_key
  idioms
  import
  imports
  imports2
  input
  intern
  isinstance
  itertools
  itertools_imports
  long
  map
  metaclass
  methodattrs
  ne
  next
  nonzero
  numliterals
  operator
  paren
  print
  raise
  raw_input
  reduce
  renames
  repr
  set_literal
  standarderror
  sys_exc
  throw
  tuple_params
  types
  unicode
  urllib
  ws_comma
  xrange
  xreadlines
  zip


Konvertierungstool "2to3" und Dateien
-------------------------------------
/usr/bin/2to3
/usr/bin/2to3-2.7
/usr/bin/2to3-3.2
/usr/share/doc/python2.7/examples/Tools/scripts/2to3
/usr/share/doc/python2.7/html/_sources/library/2to3.txt
/usr/share/doc/python2.7/html/library/2to3.html
/usr/share/doc/python3.2/examples/scripts/2to3
/usr/share/doc/python3.2/html/_sources/library/2to3.txt
/usr/share/doc/python3.2/html/library/2to3.html
/usr/share/man/man1/2to3-2.7.1.gz
/usr/share/man/man1/2to3-3.2.1.gz
/usr/share/man/man1/2to3.1.gz