Add automation for futurize patch.

[Imported from Trac: page Python3, version 73]

Python3.md

@@ -99,7 +99,7 @@ When doing the incidental fixes to other modules, try to change as little as pos
 
 **Second**, run `futurize --write --both-stages --all-imports path/to/file.py`.
 
-**Third**, fix the imports (TODO this can probably be automated).
+**Third**, fix the imports (automation below).
 
 Delete this bit:
 
@@ -118,6 +118,12 @@ if PY2:
 
 This adds builtins that match Python 3's semantics. The `#noqa: F401` keeps flake8/pyflakes from complaining about unused imports. We do unused imports so that people changing code later don't have to manually check if `map()` is old style or new style.
 
+Consider using this sed command to execute the above:
+
+```
+$ sed -ie '/from future import standard_library/d;/standard_library.install_aliases()/d;s/from builtins import \*/from future.utils import PY2\\nif PY2:\\n    from future.builtins import filter, map, zip, ascii, chr, hex, input, next, oct, open, pow, round, super, bytes, dict, list, object, range, str, max, min  # noqa: F401/' path/to/file.py
+```
+
 **Fourth**, manually review the code. Futureize is nice, but it very definitely doesn't catch everything, or it makes wrong decisions.
 
 In particular: