En Fri, 04 Sep 2009 18:43:28 -0300, Sean Talts <xitr...@gmail.com>
escribió:
I'm trying to parse some python with the compiler module, select a
subset of the AST returned, and then evaluate that subset, all in
python 2.4. It seems like in python 2.6 the compiler.ast.literal_eval
function may be what I'm looking for, but unfortunately for my project
we are restricted to using 2.4. I was wondering if there was some way
programmers performed this way back when?
Better late than never :)
This is a backport of 2.6 literal_eval using the compiler package as of
2.4; I had to add UnarySub (else -3 would be invalid) and change some
attribute names, but basically it's the same code. Untested except as
shown.
from compiler import parse
from compiler.ast import *
def literal_eval(node_or_string):
"""
Safely evaluate an expression node or a string containing a Python
expression. The string or node provided may only consist of the
following
Python literal structures: strings, numbers, tuples, lists, dicts,
booleans,
and None.
"""
_safe_names = {'None': None, 'True': True, 'False': False}
if isinstance(node_or_string, basestring):
node_or_string = parse(node_or_string, mode='eval')
if isinstance(node_or_string, Expression):
node_or_string = node_or_string.node
def _convert(node):
if isinstance(node, Const) and isinstance(node.value,
(basestring, int, float, long, complex)):
return node.value
elif isinstance(node, Tuple):
return tuple(map(_convert, node.nodes))
elif isinstance(node, List):
return list(map(_convert, node.nodes))
elif isinstance(node, Dict):
return dict((_convert(k), _convert(v)) for k, v
in node.items)
elif isinstance(node, Name):
if node.name in _safe_names:
return _safe_names[node.name]
elif isinstance(node, UnarySub):
return -_convert(node.expr)
raise ValueError('malformed string')
return _convert(node_or_string)
py> print literal_eval("(1, [-2.,'3',4j], {-5:None, u'6':True})")
(1, [-2.0, '3', 4j], {-5: None, u'6': True})
--
Gabriel Genellina
--
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