[Patches] [ python-Patches-1442442 ] Faster list comprehensions

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Patches item #1442442, was opened at 2006-03-03 07:41
Message generated for change (Comment added) made by rhettinger
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Category: Parser/Compiler
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Submitted By: Collin Winter (collinwinter)
>Assigned to: Neal Norwitz (nnorwitz)
Summary: Faster list comprehensions

Initial Comment:
The attached patch results in a 16% speed increase for
list comprehensions. By changing how the LIST_APPEND
opcode works (which was previously totally unused),
it's possible to dramatically simplify the emitted
bytecode for listcomps.

More details are available on my blog:
http://oakwinter.com/code/?p=22.

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>Comment By: Raymond Hettinger (rhettinger)
Date: 2006-03-03 11:21

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Neal, did the LIST_APPEND generation get left out of the 
AST.  In Py2.4, is was working fine:

Python 2.4.2 (#67, Sep 28 2005, 12:41:11) [MSC v.1310 32 
bit (Intel)] on win32
>>> from dis import dis
>>> dis(compile('[x for x in range(10) if x % 
2]', '', 'single'))
  1           0 BUILD_LIST               0
              3 DUP_TOP             
              4 STORE_NAME               0 (_[1])
              7 LOAD_NAME                1 (range)
             10 LOAD_CONST               0 (10)
             13 CALL_FUNCTION            1
             16 GET_ITER            
        >>   17 FOR_ITER                28 (to 48)
             20 STORE_NAME               2 (x)
             23 LOAD_NAME                2 (x)
             26 LOAD_CONST               1 (2)
             29 BINARY_MODULO       
             30 JUMP_IF_FALSE           11 (to 44)
             33 POP_TOP             
             34 LOAD_NAME                0 (_[1])
             37 LOAD_NAME                2 (x)
             40 LIST_APPEND         
             41 JUMP_ABSOLUTE           17
        >>   44 POP_TOP             
             45 JUMP_ABSOLUTE           17
        >>   48 DELETE_NAME              0 (_[1])
             51 PRINT_EXPR          
             52 LOAD_CONST               2 (None)
             55 RETURN_VALUE 

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Comment By: Collin Winter (collinwinter)
Date: 2006-03-03 07:49

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I forgot to mention: the patch also includes updates to
things like Lib/test/test_dis.py and Lib/opcode.py to make
them work with the updated LIST_APPEND opcode and code
generation.

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