def check(self, expression):
if not isinstance(expression, str):
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 _raise_not_allowed_node(self, node):
raise InvalidExpression(
"'%s' definition not allowed in python expressions" %
node.__class__.__name__)