safe exec

import ast

CODE_SAFE = 0
ERROR_IMPORT = 1
ERROR_CLASS = 2
ERROR_GLOBAL = 3
ERROR_YIELD = 4

obj_banned = {
    ast.Import: 1,
    ast.ImportFrom: 1,
    ast.ClassDef: 2,
    ast.Global: 3,
    ast.Yield: 4,
    ast.YieldFrom: 5
}


def _is_safe(node):
    if type(node) in obj_banned:
        return obj_banned[type(node)]
    return 0


def check_safe(code):
    source = ast.parse(code)
    next = [source]
    while len(next) > 0:
        new_next = []
        for obj in next:
            result = _is_safe(obj)
            if result > 0:
                return result
            new_next += ast.iter_child_nodes(obj)
        next = new_next
    return 0


def run_exec(code):
    local_space = {"message": None, "spam": None}
    exec(code, {}, local_space)
    return local_space