[Python-ideas] Augment dis.dis to autocompile strings

[Georg Brandl]

Nick Coghlan schrieb:
> Steven D'Aprano wrote:
>> On Fri, 17 Jul 2009 04:35:40 am Terry Reedy wrote:
>> 
>>> Proposal: if the input is a string, do the above (do what I mean)
>>> instead of raising
>>> TypeError: don't know how to disassemble str objects
>>>
>>> Any negatives before I submit a feature request?
>> 
>> +1 on the idea, but how do you determine which of the following are 
>> required?
>> 
>> compile('x+1', '', 'eval')
>> compile('x = x+1', '', 'single')
>> compile('while x < 42: x += 1', '', 'exec')
>> 
>> 
>> Or do you just assume 'exec'?
> 
> We could define it as trying the three in order (first 'eval', then
> 'single', then 'exec') moving on to the next option if it raises syntax
> error:
>
> from dis import dis
> def dis_str(source):
>   modes = ('eval', 'single', 'exec')
>   for mode in modes:
>     try:
>       c = compile(source, '', mode)
>       break
>     except SyntaxError:
>       if mode is modes[-1]:
>         raise
>   return dis(c)

Allowing 'single' has five unfortunate side effects: first, newlines at
the end make a difference; second, there will be PRINT_EXPRs sprinkled
in the disassembly seemingly coming from nowhere, third, statements after
the first will disappear:

>>> dis_str("for x in range(10): x\n")
  1           0 SETUP_LOOP              24 (to 27)
              3 LOAD_NAME                0 (range)
              6 LOAD_CONST               0 (10)
              9 CALL_FUNCTION            1
             12 GET_ITER
        >>   13 FOR_ITER                10 (to 26)
             16 STORE_NAME               1 (x)
             19 LOAD_NAME                1 (x)
             22 PRINT_EXPR
             23 JUMP_ABSOLUTE           13
        >>   26 POP_BLOCK
        >>   27 LOAD_CONST               1 (None)
             30 RETURN_VALUE

>>> dis_str("for x in range(10): x")
  1           0 SETUP_LOOP              24 (to 27)
              3 LOAD_NAME                0 (range)
              6 LOAD_CONST               0 (10)
              9 CALL_FUNCTION            1
             12 GET_ITER
        >>   13 FOR_ITER                10 (to 26)
             16 STORE_NAME               1 (x)
             19 LOAD_NAME                1 (x)
             22 POP_TOP
             23 JUMP_ABSOLUTE           13
        >>   26 POP_BLOCK
        >>   27 LOAD_CONST               1 (None)
             30 RETURN_VALUE

>>> dis_str("x=1\nx=2\n")
  1           0 LOAD_CONST               0 (1)
              3 STORE_NAME               0 (x)
              6 LOAD_CONST               1 (None)
              9 RETURN_VALUE

I don't think using "single" makes sense here; trying "eval" can't hurt,
though.

Georg


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