import python

import semmle.python.dataflow.new.internal.DataFlowDispatch

import semmle.python.ApiGraphs

import semmle.python.frameworks.data.internal.ApiGraphModels

predicate builtinException(string name) {

typeModel("builtins.BaseException~Subclass", "builtins." + name, "")

predicate builtinExceptionSubclass(string base, string sub) {

typeModel("builtins." + base + "~Subclass", "builtins." + sub, "")

newtype TExceptType =

TClass(Class c) or

TBuiltin(string name) { builtinException(name) }

class ExceptType extends TExceptType {

predicate incorrectExceptOrder(ExceptStmt ex1, ExceptType cls1, ExceptStmt ex2, ExceptType cls2) {

ExceptType exceptClass(ExceptStmt ex) { ex.getType() = result.getAUse().asExpr() }

from ExceptStmt ex1, ExceptType cls1, ExceptStmt ex2, ExceptType cls2, string msg

incorrectExceptOrder(ex1, cls1, ex2, cls2) and

if cls1 = cls2

then msg = "This except block handling $@ is unreachable; as $@ also handles $@."

else

msg =

"This except block handling $@ is unreachable; as $@ for the more general $@ always subsumes it."

select ex2, msg, cls2, cls2.getName(), ex1, "this except block", cls1, cls1.getName()