namespace if it occurs as a free variable in a nested block.  This limitation
of the compiler has been lifted, and a new opcode introduced (DELETE_DEREF).

This sample was valid in 2.6, but fails to compile in 3.x without this change::

   >>> def f():
   ...     def print_error():
   ...        print(e)
   ...     try:
   ...        something
   ...     except Exception as e:
   ...        print_error()
   ...        # implicit "del e" here


This sample has always been invalid in Python, and now works::

   >>> def outer(x):
   ...     def inner():
   ...        return x
   ...     inner()
   ...     del x

There is no need to bump the PYC magic number: the new opcode is used
for code that did not compile before.

by the new (and simpler) DUP_TOP_TWO.  Performance isn't changed, but
our bytecode is a bit simplified.  Patch by Demur Rumed.

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r72912 | benjamin.peterson | 2009-05-25 08:13:44 -0500 (Mon, 25 May 2009) | 5 lines

  add a SETUP_WITH opcode

  It speeds up the with statement and correctly looks up the special
  methods involved.
........
  r72920 | benjamin.peterson | 2009-05-25 15:12:57 -0500 (Mon, 25 May 2009) | 1 line

  take into account the fact that SETUP_WITH pushes a finally block
........
  r72940 | benjamin.peterson | 2009-05-26 07:49:59 -0500 (Tue, 26 May 2009) | 1 line

  teach the peepholer about SETUP_WITH
........

It speeds up the with statement and correctly looks up the special
methods involved.

POP_JUMP_IF_{TRUE,FALSE} and JUMP_IF_{TRUE,FALSE}_OR_POP. This avoids executing
a POP_TOP on each conditional and sometimes allows the peephole optimizer to
skip a JUMP_ABSOLUTE entirely. It speeds up list comprehensions significantly.

This patch by Antoine Pitrou optimizes the bytecode for conditional branches by
merging the following "POP_TOP" instruction into the conditional jump.  For
example, the list comprehension "[x for x in l if not x]" produced the
following bytecode:

  1           0 BUILD_LIST               0
              3 LOAD_FAST                0 (.0)
        >>    6 FOR_ITER                23 (to 32)
              9 STORE_FAST               1 (x)
             12 LOAD_FAST                1 (x)
             15 JUMP_IF_TRUE            10 (to 28)
             18 POP_TOP
             19 LOAD_FAST                1 (x)
             22 LIST_APPEND              2
             25 JUMP_ABSOLUTE            6
        >>   28 POP_TOP
             29 JUMP_ABSOLUTE            6
        >>   32 RETURN_VALUE

but after the patch it produces the following bytecode:

  1           0 BUILD_LIST               0
              3 LOAD_FAST                0 (.0)
        >>    6 FOR_ITER                18 (to 27)
              9 STORE_FAST               1 (x)
             12 LOAD_FAST                1 (x)
             15 POP_JUMP_IF_TRUE         6
             18 LOAD_FAST                1 (x)
             21 LIST_APPEND              2
             24 JUMP_ABSOLUTE            6
        >>   27 RETURN_VALUE

Notice that not only the code is shorter, but the conditional jump
(POP_JUMP_IF_TRUE) jumps right to the start of the loop instead of going through
the JUMP_ABSOLUTE at the end. "continue" statements are helped
similarly.

Furthermore, the old jump opcodes (JUMP_IF_FALSE, JUMP_IF_TRUE) have been
replaced by two new opcodes:
- JUMP_IF_TRUE_OR_POP, which jumps if true and pops otherwise
- JUMP_IF_FALSE_OR_POP, which jumps if false and pops otherwise

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r67818 | antoine.pitrou | 2008-12-17 01:38:28 +0100 (mer., 17 déc. 2008) | 3 lines

  Issue #2183: Simplify and optimize bytecode for list comprehensions.
........

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r59544 | raymond.hettinger | 2007-12-18 01:13:45 +0100 (Tue, 18 Dec 2007) | 1 line

  Add more namedtuple() test cases.  Neaten the code and comments.
........
  r59545 | christian.heimes | 2007-12-18 04:38:03 +0100 (Tue, 18 Dec 2007) | 3 lines

  Fixed for #1601: IDLE not working correctly on Windows (Py30a2/IDLE30a1)

  Amaury's ideas works great. Should we build the Python core with WINVER=0x0500 and _WIN32_WINNT=0x0500, too?
........
  r59546 | christian.heimes | 2007-12-18 10:00:13 +0100 (Tue, 18 Dec 2007) | 1 line

  Make it a bit easier to test Tcl/Tk and idle from a build dir.
........
  r59547 | christian.heimes | 2007-12-18 10:12:10 +0100 (Tue, 18 Dec 2007) | 1 line

  Removed several unused files from the PCbuild9 directory. They are relics from the past.
........
  r59548 | raymond.hettinger | 2007-12-18 19:26:18 +0100 (Tue, 18 Dec 2007) | 29 lines

  Speed-up dictionary constructor by about 10%.

  New opcode, STORE_MAP saves the compiler from awkward stack manipulations
  and specializes for dicts using PyDict_SetItem instead of PyObject_SetItem.

  Old disassembly:
                0 BUILD_MAP                0
                3 DUP_TOP
                4 LOAD_CONST               1 (1)
                7 ROT_TWO
                8 LOAD_CONST               2 ('x')
               11 STORE_SUBSCR
               12 DUP_TOP
               13 LOAD_CONST               3 (2)
               16 ROT_TWO
               17 LOAD_CONST               4 ('y')
               20 STORE_SUBSCR

  New disassembly:
                0 BUILD_MAP                0
                3 LOAD_CONST               1 (1)
                6 LOAD_CONST               2 ('x')
                9 STORE_MAP
               10 LOAD_CONST               3 (2)
               13 LOAD_CONST               4 ('y')
               16 STORE_MAP
........
  r59549 | thomas.heller | 2007-12-18 20:00:34 +0100 (Tue, 18 Dec 2007) | 2 lines

  Issue #1642: Fix segfault in ctypes when trying to delete attributes.
........
  r59551 | guido.van.rossum | 2007-12-18 21:10:42 +0100 (Tue, 18 Dec 2007) | 2 lines

  Issue #1645 by Alberto Bertogli.  Fix a comment.
........
  r59553 | raymond.hettinger | 2007-12-18 22:24:09 +0100 (Tue, 18 Dec 2007) | 12 lines

  Give meaning to the oparg for BUILD_MAP:  estimated size of the dictionary.

  Allows dictionaries to be pre-sized (upto 255 elements) saving time lost
  to re-sizes with their attendant mallocs and re-insertions.

  Has zero effect on small dictionaries (5 elements or fewer), a slight
  benefit for dicts upto 22 elements (because they had to resize once
  anyway), and more benefit for dicts upto 255 elements (saving multiple
  resizes during the build-up and reducing the number of collisions on
  the first insertions).  Beyond 255 elements, there is no addional benefit.
........
  r59554 | christian.heimes | 2007-12-18 22:56:09 +0100 (Tue, 18 Dec 2007) | 1 line

  Fixed #1649: IDLE error: dictionary changed size during iteration
........
  r59557 | raymond.hettinger | 2007-12-18 23:21:27 +0100 (Tue, 18 Dec 2007) | 1 line

  Simplify and speedup _asdict() for named tuples.
........
  r59558 | christian.heimes | 2007-12-19 00:22:54 +0100 (Wed, 19 Dec 2007) | 3 lines

  Applied patch #1635: Float patch for inf and nan on Windows (and other platforms).

  The patch unifies float("inf") and repr(float("inf")) on all platforms.
........
  r59559 | raymond.hettinger | 2007-12-19 00:51:15 +0100 (Wed, 19 Dec 2007) | 1 line

  Users demand iterable input for named tuples. The author capitulates.
........
  r59560 | raymond.hettinger | 2007-12-19 01:21:06 +0100 (Wed, 19 Dec 2007) | 1 line

  Beef-up tests for dict literals
........
  r59561 | raymond.hettinger | 2007-12-19 01:27:21 +0100 (Wed, 19 Dec 2007) | 1 line

  Zap a duplicate line
........

Allows dictionaries to be pre-sized (upto 255 elements) saving time lost
to re-sizes with their attendant mallocs and re-insertions.

Has zero effect on small dictionaries (5 elements or fewer), a slight
benefit for dicts upto 22 elements (because they had to resize once
anyway), and more benefit for dicts upto 255 elements (saving multiple
resizes during the build-up and reducing the number of collisions on
the first insertions).  Beyond 255 elements, there is no addional benefit.

New opcode, STORE_MAP saves the compiler from awkward stack manipulations
and specializes for dicts using PyDict_SetItem instead of PyObject_SetItem.

Old disassembly:
              0 BUILD_MAP                0
              3 DUP_TOP
              4 LOAD_CONST               1 (1)
              7 ROT_TWO
              8 LOAD_CONST               2 ('x')
             11 STORE_SUBSCR
             12 DUP_TOP
             13 LOAD_CONST               3 (2)
             16 ROT_TWO
             17 LOAD_CONST               4 ('y')
             20 STORE_SUBSCR

New disassembly:
              0 BUILD_MAP                0
              3 LOAD_CONST               1 (1)
              6 LOAD_CONST               2 ('x')
              9 STORE_MAP
             10 LOAD_CONST               3 (2)
             13 LOAD_CONST               4 ('y')
             16 STORE_MAP

The compiler package hasn't been updated yet; test_compiler.py fails.
Otherwise all tests seem to be passing now.  There are no occurrences
of __metaclass__ left in the standard library.
Docs have not been updated.

* Fix some docstrings and one Print -> print.
* Fix test_{class,code,descrtut,dis,extcall,parser,popen,pkg,subprocess,syntax,traceback}.
  These were the ones that generated code with a print statement.
  In most remaining failing tests there's an issue with the soft space.

import MAGIC number.

This was started by Mike Bland and completed by Guido
(with help from Neal).

This still needs a __future__ statement added;
Thomas is working on Michael's patch for that aspect.

There's a small amount of code cleanup and refactoring
in ast.c, compile.c and ceval.c (I fixed the lltrace
behavior when EXT_POP is used -- however I had to make
lltrace a static global).

Reduces the cost of "not" to almost zero.

Add a new opcode, LIST_APPEND, and apply it to the code generation for
list comprehensions.  Reduces the per-loop overhead by about a third.

From SF patch #852334.

The additional code complexity and new NOP opcode were not worth it.

* Can now test for basic blocks.
* Optimize inverted comparisions.
* Optimize unary_not followed by a conditional jump.
* Added a new opcode, NOP, to keep code size constant.
* Applied NOP to previous transformations where appropriate.

Note, the NOP would not be necessary if other functions were
added to re-target jump addresses and update the co_lnotab mapping.
That would yield slightly faster and cleaner bytecode at the
expense of optimizer simplicity and of keeping it decoupled
from the line-numbering structure.

should be generated automatically