Hello-
I am trying to get Python to extract attributes in full dotted form
from compiled expression. For instance, if I have the following:
param = compile('a.x + a.y','','single')
then I would like to retrieve the list consisting of ['a.x','a.y'].
I have tried using inspect to look at 'co_names', but when I do that,
I get:
>>> inspect.getmembers(param)[23]
('co_names', ('a', 'x', 'y'))
with no way to determine that 'x' and 'y' are both attributes of 'a'.
The reason I am attempting this is to try and automatically determine
data dependencies in a user-supplied formula (in order to build a
dataflow network). I would prefer not to have to write my own parser
just yet.
Alternatively, I've looked at the parser module, but I am experiencing
some difficulties in that the symbol list does not seem to match that
listed in the python grammar reference (not surprising, since I am
using python2.5, and the docs seem a bit dated)
In particular:
>>> import parser
>>> import pprint
>>> import symbol
>>> tl=parser.expr("a.x").tolist()
>>> pprint.pprint(tl)
[258,
[326,
[303,
[304,
[305,
[306,
[307,
[309,
[310,
[311,
[312,
[313,
[314,
[315,
[316, [317, [1, 'a']], [321, [23, '.'], [1,
'x']]]]]]]]]]]]]]]],
[4, ''],
[0, '']]
>>> print symbol.sym_name[316]
power
Thus, for some reason, 'a.x' seems to be interpreted as a power
expression, and not an 'attributeref' as I would have anticipated (in
fact, the symbol module does not seem to contain an 'attributeref'
symbol)
(for the curious, here is the relevant part of the AST for "a**x":
[316,
[317, [1, 'a']],
[36, '**'],
[315, [316, [317, [1, 'x']]]]
)
Anyway, I could write an AST analyzer that searches for the correct
pattern, but it would be relying on undocumented behavior, and I'm
hoping there is a better way.
(By the way, I realize that malicious users could almost certainly
subvert my proposed dependency mechanism, but for this project, I'm
guarding against Murphy, not Macchiavelli)
Thanks,
-matt
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