[Subversion] / BytecodeAssembler / README.txt  

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version 2453, Sat Dec 29 19:29:57 2007 UTC version 2457, Sun Dec 30 20:10:36 2007 UTC
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 Changes since version 0.2:  Changes since version 0.2:
   
 * Added a ``Getattr`` symbol that does static or dynamic attribute access and  * Added ``Suite``, ``TryExcept``, and ``TryFinally`` node types
   constant folding  
   * Added a ``Getattr`` node type that does static or dynamic attribute access
     and constant folding
   
 * Fixed ``code.from_function()`` not copying the ``co_filename`` attribute when  * Fixed ``code.from_function()`` not copying the ``co_filename`` attribute when
   ``copy_lineno`` was specified.    ``copy_lineno`` was specified.
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                   6 LOAD_CONST               3 (1.0)                    6 LOAD_CONST               3 (1.0)
                   9 LOAD_CONST               4 (1L)                    9 LOAD_CONST               4 (1L)
   
   
 Simple Containers  Simple Containers
 -----------------  -----------------
   
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     False      False
   
   
   ``Suite`` and ``Pass``
   ----------------------
   
   On occasion, it's helpful to be able to group a sequence of opcodes,
   expressions, or statements together, to be passed as an argument to other node
   types.  The ``Suite`` node type accomplishes this::
   
       >>> from peak.util.assembler import Suite, Pass
   
       >>> c = Code()
       >>> c.return_(Suite([Const(42), Code.DUP_TOP, Code.POP_TOP]))
       >>> dis(c.code())
         0           0 LOAD_CONST               1 (42)
                     3 DUP_TOP
                     4 POP_TOP
                     5 RETURN_VALUE
   
   And ``Pass`` is a shortcut for an empty ``Suite``, that generates nothing::
   
       >>> Suite([])
       Pass
   
       >>> c = Code()
       >>> c(Pass)
       >>> c.return_(None)
       >>> dis(c.code())
         0           0 LOAD_CONST               0 (None)
                     3 RETURN_VALUE
   
   
 Local and Global Names  Local and Global Names
 ----------------------  ----------------------
   
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 code that might be unreachable.  For example, consider this ``If``  code that might be unreachable.  For example, consider this ``If``
 implementation::  implementation::
   
     >>> from peak.util.assembler import Pass  
     >>> def If(cond, then, else_=Pass, code=None):      >>> def If(cond, then, else_=Pass, code=None):
     ...     if code is None:      ...     if code is None:
     ...         return cond, then, else_      ...         return cond, then, else_
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             >>   10 LOAD_CONST               0 (None)              >>   10 LOAD_CONST               0 (None)
                  13 RETURN_VALUE                   13 RETURN_VALUE
   
 Labels have a ``POP_BLOCK`` attribute that you can pass in when generating  (Labels have a ``POP_BLOCK`` attribute that you can pass in when generating
 code.  code.)
   
   And, for generating typical try/except blocks, you can use the ``TryExcept``
   node type, which takes a body, a sequence of exception-type/handler pairs,
   and an optional "else" clause::
   
       >>> from peak.util.assembler import TryExcept
       >>> c = Code()
       >>> c.return_(
       ...     TryExcept(
       ...         Return(1),                                      # body
       ...         [(Const(KeyError),2), (Const(TypeError),3)],    # handlers
       ...         Return(4)                                       # else clause
       ...     )
       ... )
   
       >>> dis(c.code())
         0           0 SETUP_EXCEPT             8 (to 11)
                     3 LOAD_CONST               1 (1)
                     6 RETURN_VALUE
                     7 POP_BLOCK
                     8 JUMP_FORWARD            43 (to 54)
               >>   11 DUP_TOP
                    12 LOAD_CONST               2 (<type 'exceptions.KeyError'>)
                    15 COMPARE_OP              10 (exception match)
                    18 JUMP_IF_FALSE           10 (to 31)
                    21 POP_TOP
                    22 POP_TOP
                    23 POP_TOP
                    24 POP_TOP
                    25 LOAD_CONST               3 (2)
                    28 JUMP_FORWARD            27 (to 58)
               >>   31 POP_TOP
                    32 DUP_TOP
                    33 LOAD_CONST               4 (<type 'exceptions.TypeError'>)
                    36 COMPARE_OP              10 (exception match)
                    39 JUMP_IF_FALSE           10 (to 52)
                    42 POP_TOP
                    43 POP_TOP
                    44 POP_TOP
                    45 POP_TOP
                    46 LOAD_CONST               5 (3)
                    49 JUMP_FORWARD             6 (to 58)
               >>   52 POP_TOP
                    53 END_FINALLY
               >>   54 LOAD_CONST               6 (4)
                    57 RETURN_VALUE
               >>   58 RETURN_VALUE
   
   
 Try/Finally Blocks  Try/Finally Blocks
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 adjusts the maximum expected stack size to accomodate up to three values being  adjusts the maximum expected stack size to accomodate up to three values being
 put on the stack by the Python interpreter for exception handling.  put on the stack by the Python interpreter for exception handling.
   
   For your convenience, the ``TryFinally`` node type can also be used to generate
   try/finally blocks::
   
       >>> from peak.util.assembler import TryFinally
       >>> c = Code()
       >>> c( TryFinally(ExprStmt(1), ExprStmt(2)) )
       >>> dis(c.code())
         0           0 SETUP_FINALLY            8 (to 11)
                     3 LOAD_CONST               1 (1)
                     6 POP_TOP
                     7 POP_BLOCK
                     8 LOAD_CONST               0 (None)
               >>   11 LOAD_CONST               2 (2)
                    14 POP_TOP
                    15 END_FINALLY
   
   
 Loops  Loops
 -----  -----
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     >>> from peak.util.assembler import LOAD_CONST, POP_BLOCK      >>> from peak.util.assembler import LOAD_CONST, POP_BLOCK
   
     >>> def Pass(code=None):  
     ...     if code is None:  
     ...         return Pass  
   
     >>> import sys      >>> import sys
     >>> WHY_CONTINUE = {'2.3':5, '2.4':32, '2.5':32}[sys.version[:3]]      >>> WHY_CONTINUE = {'2.3':5, '2.4':32, '2.5':32}[sys.version[:3]]
   

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