def convert(self, expr): 
ast_queue = [[expr]]<EOL>arg_queue = []<EOL>op_queue = []<EOL>try:<EOL><INDENT>while ast_queue:<EOL><INDENT>args_list = ast_queue[-<NUM_LIT:1>]<EOL>if args_list:<EOL><INDENT>ast = args_list.pop(<NUM_LIT:0>)<EOL>if type(ast) in {bool, int, str, float} or not isinstance(ast, Base):<EOL><INDENT>converted = self._convert(ast)<EOL>arg_queue.append(converted)<EOL>continue<EOL><DEDENT>if self in ast._errored:<EOL><INDENT>raise BackendError("<STR_LIT>"<EOL>"<STR_LIT>" % (self, ast.op, ast.__class__.__name__))<EOL><DEDENT>if self._cache_objects:<EOL><INDENT>cached_obj = self._object_cache.get(ast._cache_key, None)<EOL>if cached_obj is not None:<EOL><INDENT>arg_queue.append(cached_obj)<EOL>continue<EOL><DEDENT><DEDENT>op_queue.append(ast)<EOL>if ast.op in self._op_expr:<EOL><INDENT>ast_queue.append(None)<EOL><DEDENT>else:<EOL><INDENT>ast_queue.append(list(ast.args))<EOL><DEDENT><DEDENT>else:<EOL><INDENT>ast_queue.pop()<EOL>if op_queue:<EOL><INDENT>ast = op_queue.pop()<EOL>op = self._op_expr.get(ast.op, None)<EOL>if op is not None:<EOL><INDENT>r = op(ast)<EOL><DEDENT>else:<EOL><INDENT>args = arg_queue[-len(ast.args):]<EOL>del arg_queue[-len(ast.args):]<EOL>try:<EOL><INDENT>r = self._call(ast.op, args)<EOL><DEDENT>except BackendUnsupportedError:<EOL><INDENT>r = self.default_op(ast)<EOL><DEDENT><DEDENT>for a in ast.annotations:<EOL><INDENT>r = self.apply_annotation(r, a)<EOL><DEDENT>if self._cache_objects:<EOL><INDENT>self._object_cache[ast._cache_key] = r<EOL><DEDENT>arg_queue.append(r)<EOL><DEDENT><DEDENT><DEDENT><DEDENT>except (RuntimeError, ctypes.ArgumentError) as e:<EOL><INDENT>raise ClaripyRecursionError("<STR_LIT>") from e<EOL><DEDENT>except BackendError:<EOL><INDENT>for ast in op_queue:<EOL><INDENT>ast._errored.add(self)<EOL><DEDENT>if isinstance(expr, Base):<EOL><INDENT>expr._errored.add(self)<EOL><DEDENT>raise<EOL><DEDENT>return arg_queue.pop()<EOL>
Resolves a claripy.ast.Base into something usable by the backend.

:param expr:    The expression.
:param save:    Save the result in the expression's object cache
:return:        A backend object.