Fixing bug

[#448679] Left to right

* Python/compile.c
  (com_dictmaker): Reordered evaluation of dictionaries to follow strict
  LTR evaluation.

* Lib/compiler/pycodegen.py
  (CodeGenerator.visitDict): Reordered evaluation of dictionaries to
  follow strict LTR evaluation.

* Doc/ref/ref5.tex
  Documented the general LTR evaluation order idea.

* Misc/NEWS
  Documented change in evaluation order of dictionaries.

diff --git a/Doc/ref/ref5.tex b/Doc/ref/ref5.tex
index 34c99efa96e7c999db9d6e690e0413512e47847d..c0212d03e1239f415653eeed525675a1b7dbfaf7 100644 (file)
--- a/Doc/ref/ref5.tex
+++ b/Doc/ref/ref5.tex
@@ -1026,6 +1026,24 @@ tuple, but rather yields the value of that expression.
 \code{()}.)
 \indexii{trailing}{comma}
 
+\section{Evaluation order\label{evalorder}}
+\indexii{evaluation}{order}
+
+Python evaluates expressions from left to right. Notice that while
+evaluating an assignment, the right-hand side is evaluated before
+the left-hand side.
+
+In the following lines, expressions will be evaluated in the
+arithmetic order of their suffixes:
+
+\begin{verbatim}
+expr1, expr2, expr3, expr4
+(expr1, expr2, expr3, expr4)
+{expr1: expr2, expr3: expr4}
+expr1 + expr2 * (expr3 - expr4)
+func(expr1, expr2, *expr3, **expr4)
+expr3, expr4 = expr1, expr2
+\end{verbatim}
 
 \section{Summary\label{summary}}
 

diff --git a/Lib/compiler/pycodegen.py b/Lib/compiler/pycodegen.py
index a0aa73a7395c2847d59f41b4a86cbb4bd4011ed8..ac978c088e64037dd2099cb9834eb2899b8aa862 100644 (file)
--- a/Lib/compiler/pycodegen.py
+++ b/Lib/compiler/pycodegen.py
@@ -1129,9 +1129,9 @@ class CodeGenerator:
                 self.emit('SET_LINENO', lineno2)
                 lineno = lineno2
             self.emit('DUP_TOP')
-            self.visit(v)
-            self.emit('ROT_TWO')
             self.visit(k)
+            self.visit(v)
+            self.emit('ROT_THREE')
             self.emit('STORE_SUBSCR')
 
 class NestedScopeMixin:

diff --git a/Misc/NEWS b/Misc/NEWS
index 12df9ec82d02b8f18eaa882c9332bf3fef681c34..dea62dd2db5c1bd2532986e0aa1353a90a8f1722 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -331,6 +331,10 @@ Core and builtins
 - sys.exit() inadvertently allowed more than one argument.
   An exception will now be raised if more than one argument is used.
 
+- Changed evaluation order of dictionaries to conform to the general
+  left to right evaluation order rule. Now {f1(): f2()} will evaluate
+  f1 first.
+
 Extension modules
 -----------------
 

diff --git a/Python/compile.c b/Python/compile.c
index b438ce44f989dbfa461143e3e8a15918565b5319..17555219d4a51fb6269953d87aed10989e12700c 100644 (file)
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -1529,9 +1529,9 @@ com_dictmaker(struct compiling *c, node *n)
                   It wants the stack to look like (value) (dict) (key) */
                com_addbyte(c, DUP_TOP);
                com_push(c, 1);
-               com_node(c, CHILD(n, i+2)); /* value */
-               com_addbyte(c, ROT_TWO);
                com_node(c, CHILD(n, i)); /* key */
+               com_node(c, CHILD(n, i+2)); /* value */
+               com_addbyte(c, ROT_THREE);
                com_addbyte(c, STORE_SUBSCR);
                com_pop(c, 3);
        }