upadte from Aahz

pep-0328.txt

@@ -41,10 +41,11 @@ In Python 2.4, you must enable the new absolute import behavior with ::
     from __future__ import absolute_import
 
 You may use relative imports freely.  In Python 2.5, any ``import``
-statement that results in an intra-package import will generate a
-``PendingDeprecation`` warning (this also applies to ``from <> import``
-that fails to use the relative import syntax).  In Python 2.6, ``import``
-will always be an absolute import.
+statement that results in an intra-package import will raise
+``DeprecationWarning`` (this also applies to ``from <> import`` that
+fails to use the relative import syntax).  In Python 2.6, ``import`` will
+always be an absolute import (and the ``__future__`` directive will no
+longer be needed).
 
 
 Rationale for Parentheses
@@ -71,33 +72,37 @@ mechanism (parentheses) to write the ``import`` statement::
     from Tkinter import (Tk, Frame, Button, Entry, Canvas, Text,
         LEFT, DISABLED, NORMAL, RIDGE, END)
 
-This part of the proposal already has BDFL approval.
+This part of the proposal had BDFL approval from the beginning.
 
 
 Rationale for Absolute Imports
 ==============================
 
-In current Python, if you're reading a module located inside a
+In Python 2.3 and earlier, if you're reading a module located inside a
 package, it is not clear whether ::
 
     import foo
 
 refers to a top-level module or to another module inside the package.
-Let's say today it refers to a module internal to the package.  Then
-tomorrow, the standard library decides to add its own foo package that
-you'd like to use.  You can't without renaming your internal module.
-To resolve these ambiguities, it is proposed that ``foo`` will always be a
-module or package reachable from ``sys.path``.
+As Python's library expands, more and more existing package internal
+modules suddenly shadow standard library modules by accident.  It's a
+particularly difficult problem inside packages because there's no way to
+specify which module is meant.  To resolve the ambiguity, it is proposed
+that ``foo`` will always be a module or package reachable from
+``sys.path``.  This is called an absolute import.
+
+The python-dev community chose absolute imports as the default because
+they're the more common use case and because absolute imports can provide
+all the functionality of relative (intra-package) imports  -- albeit at
+the cost of difficulty when renaming package pieces higher up in the
+hierarchy or when moving one package inside another.
 
 Because this represents a change in semantics, absolute imports will
-be optional in Python 2.4 through the use of ::
+be optional in Python 2.4 and 2.5 through the use of ::
 
     from __future__ import absolute_import
 
-This PEP will be updated when it is decided to make absolute imports
-the default, probably Python 2.5 or 2.6.
-
-This part of the proposal already has BDFL approval.
+This part of the proposal had BDFL approval from the beginning.
 
 
 Rationale for Relative Imports
@@ -207,22 +212,28 @@ Here are the contenders:
 
 
 Guido's Decision
-----------------
+================
 
-Guido has Pronounced [1]_ that relative imports will use leading dots,
-one per level of parent.  Further discussion led to the following
-clarification of the semantics.  Given a package layout::
+Guido has Pronounced [1]_ that relative imports will use leading dots.
+A single leading dot indicates a relative import, starting with the
+current package.  Two or more leading dots give a relative import to the
+parent(s) of the current package, one level per dot after the first.
+Here's a sample package layout::
 
-    package
-        subpackage1
-            moduleX
-            moduleY
-        subpackage2
-            moduleZ
-        moduleA
+    package/
+        __init__.py
+        subpackage1/
+            __init__.py
+            moduleX.py
+            moduleY.py
+        subpackage2/
+            __init__.py
+            moduleZ.py
+        moduleA.py
 
-Assuming that the current file is ``moduleX.py``, following are correct
-usages of the new syntax::
+Assuming that the current file is either ``moduleX.py`` or
+``subpackage1/__init__.py``, following are correct usages of the new
+syntax::
 
     from .moduleY import spam
     from .moduleY import spam as ham
@@ -236,9 +247,23 @@ usages of the new syntax::
 Note that while that last case is legal, it is certainly discouraged
 ("insane" was the word Guido used).
 
-Reminder: relative imports must always use ``from <> import``;
-``import <>`` is always absolute.  Of course, absolute imports can use
-``from <> import`` by omitting the leading dots.
+Relative imports must always use ``from <> import``; ``import <>`` is
+always absolute.  Of course, absolute imports can use ``from <> import``
+by omitting the leading dots.  The reason ``import .foo`` is prohibited
+is because after ::
+
+    import XXX.YYY.ZZZ
+
+then ::
+
+    XXX.YYY.ZZZ
+
+is usable in an expression.  But ::
+
+    .moduleY
+
+is not usable in an expression.
+