from __future__ import absolute_import
import six
import ast
from spidermon.exceptions import InvalidExpression
class Interpreter(object):
ast_allowed_nodes = (
"expr",
"name",
"load",
"call",
"store",
"str",
"unicode",
"num",
"list",
"dict",
"set",
"tuple", # Data types
"nameconstant", # language constant (None)
"unaryop",
"usub", # Unary arithmetic operators
"binop",
"add",
"sub",
"div",
"mult",
"mod",
"pow",
"floordiv", # Binary arithmetic operators
"compare",
"eq",
"noteq",
"gt",
"lt",
"gte",
"lte", # Comparison operators
"bitand",
"bitor",
"bitxor",
"invert",
"lshift",
"rshift", # Bitwise operators
"boolop",
"and",
"or",
"not", # Logical operators
"in",
"notin", # Membership operators
"is",
"isnot", # Identity operators
"ifexp", # Inline if statement
"subscript",
"index",
"slice",
"extslice", # Subscripting
"listcomp",
"setcomp",
"dictcomp",
"generatorexp",
"comprehension", # Comprehensions
"attribute", # Attribute access
)
allowed_objects = (
str,
six.text_type, # strings
int,
float,
complex, # numbers
list,
dict,
set,
tuple, # sequences
type(None),
bool, # others
)
def check(self, expression):
if not isinstance(expression, six.string_types):
raise InvalidExpression("Python expressions must be defined as strings")
if not expression:
raise InvalidExpression("Empty python expression")
try:
tree = ast.parse(expression)
except SyntaxError as e:
raise e
if not tree.body:
raise InvalidExpression("Empty python expression")
elif len(tree.body) > 1:
raise InvalidExpression(
"Python expressions must be a single line expression"
)
start_node = tree.body[0]
if not isinstance(start_node, ast.Expr):
raise InvalidExpression(
"Python string must be an expression: '%s' found"
% start_node.__class__.__name__
)
self._check_node(start_node)
def eval(self, expression, context=None, check=True):
if check:
self.check(expression)
return eval(expression, context)
def _check_node(self, node):
if isinstance(node, list):
self._check_node_list(node)
elif isinstance(node, ast.AST):
if not self._is_allowed_ast_node(node):
self._raise_not_allowed_node(node)
self._check_node_fields(node)
elif not isinstance(node, self.allowed_objects):
self._raise_not_allowed_node(node)
def _check_node_list(self, node_list):
for node in node_list:
self._check_node(node)
def _check_node_fields(self, node):
for field in [f for _, f in ast.iter_fields(node)]:
self._check_node(field)
def _is_allowed_ast_node(self, node):
return node.__class__.__name__.lower() in self.ast_allowed_nodes
def _raise_not_allowed_node(self, node):
raise InvalidExpression(
"'%s' definition not allowed in python expressions"
% node.__class__.__name__
)
