##############################################################################
#
# Copyright (c) 2002 Zope Foundation and Contributors.
#
# This software is subject to the provisions of the Zope Public License,
# Version 2.1 (ZPL). A copy of the ZPL should accompany this distribution.
# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
# FOR A PARTICULAR PURPOSE
#
##############################################################################
"""Restricted Python Expressions."""
import ast
from .compile import compile_restricted_eval
nltosp = str.maketrans('\r\n', ' ')
# No restrictions.
default_guarded_getattr = getattr
def default_guarded_getitem(ob, index):
# No restrictions.
return ob[index]
def default_guarded_getiter(ob):
# No restrictions.
return ob
class RestrictionCapableEval:
"""A base class for restricted code."""
globals = {'__builtins__': None}
# restricted
rcode = None
# unrestricted
ucode = None
# Names used by the expression
used = None
def __init__(self, expr):
"""Create a restricted expression
where:
expr -- a string containing the expression to be evaluated.
"""
expr = expr.strip()
self.__name__ = expr
expr = expr.translate(nltosp)
self.expr = expr
# Catch syntax errors.
self.prepUnrestrictedCode()
def prepRestrictedCode(self):
if self.rcode is None:
result = compile_restricted_eval(self.expr, '<string>')
if result.errors:
raise SyntaxError(result.errors[0])
self.used = tuple(result.used_names)
self.rcode = result.code
def prepUnrestrictedCode(self):
if self.ucode is None:
exp_node = compile(
self.expr,
'<string>',
'eval',
ast.PyCF_ONLY_AST)
co = compile(exp_node, '<string>', 'eval')
# Examine the ast to discover which names the expression needs.
if self.used is None:
used = set()
for node in ast.walk(exp_node):
if isinstance(node, ast.Name):
if isinstance(node.ctx, ast.Load):
used.add(node.id)
self.used = tuple(used)
self.ucode = co
def eval(self, mapping):
# This default implementation is probably not very useful. :-(
# This is meant to be overridden.
self.prepRestrictedCode()
global_scope = {
'_getattr_': default_guarded_getattr,
'_getitem_': default_guarded_getitem,
'_getiter_': default_guarded_getiter,
}
global_scope.update(self.globals)
for name in self.used:
if (name not in global_scope) and (name in mapping):
global_scope[name] = mapping[name]
return eval(self.rcode, global_scope)
def __call__(self, **kw):
return self.eval(kw)