assertion failure at Objects/call.c:618: PyObject *callmethod(PyThreadState *, PyObject *, const char *, struct __va_list_tag *): Assertion 'callable != NULL' failed.

Crash report

What happened?

import builtins
import sys

def test_import(name, *args, **kwargs):
    sys.modules[name] = object()
    return sys.modules[name]

builtins.__import__ = test_import

raise RuntimeError("Test")

python: ../Objects/call.c:618: PyObject *callmethod(PyThreadState *, PyObject *, const char *, struct __va_list_tag *): Assertion `callable != NULL' failed.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

No response

Linked PRs

Full message (please include it when possible):

Exception ignored in the internal traceback machinery:
AttributeError: 'object' object has no attribute '_print_exception_bltin'
Traceback (most recent call last):
  File "/home/bswck/Python/cpython/t.py", line 12, in <module>
python: Objects/call.c:618: callmethod: Assertion `callable != NULL' failed.
Fatal Python error: Aborted
Aborted (core dumped)

The problem happens because _Py_FindSourceFile resorts to _PyObject_CallMethodFormat which assumes callable is healthy (the callable in this case is the result of getting open of io, which is NULL because io is an object() from test_import).
Maybe NULL-check the callable first? (PR in progress)

Maybe NULL-check the callable first? (PR in progress)

I think the issue is here:

cpython/Python/traceback.c

Lines 417 to 420 in 14d3974

    
           open = PyObject_GetAttr(io, &_Py_ID(open)); 
        
           for (i = 0; i < npath; i++) { 
        
               v = PyList_GetItem(syspath, i); 
        
               if (v == NULL) {

We need to check for a NULL result from PyObject_GetAttr, not defer the check to _PyObject_CallMethodFormat, because:

That will slow things down for other callers.
It's generally unsafe to call arbitrary C API functions with an exception set.

Would slow down for other callers of _Py_FindSourceFile -- there are no other callers of _PyObject_CallMethodFormat than traceback.c itself.

I think we can skip the entire loop actually, if open is NULL?

Would slow down for other callers of _Py_FindSourceFile -- there are no other callers of _PyObject_CallMethodFormat than traceback.c itself.

Then I assume that API was added with the intention that we'll use it somewhere else someday.

I think we can skip the entire loop actually, if open is NULL?

Yeah, that makes sense to me.

gh-142737: Handle lost `io.open` in `_Py_FindSourceFile` (GH-142747)

pythongh-142737: Handle lost `io.open` in `_Py_FindSourceFile` (pytho…

[3.13] pythongh-142737: Handle lost `io.open` in `_Py_FindSourceFile` (…

[3.13] gh-142737: Handle lost `io.open` in `_Py_FindSourceFile` (GH-1…

[3.14] gh-142737: Handle lost `io.open` in `_Py_FindSourceFile` (GH-1…

pythongh-142737: Handle lost `io.open` in `_Py_FindSourceFile` (pytho…

Navigation Menu

Repository navigation

assertion failure at Objects/call.c:618: `PyObject callmethod(PyThreadState , PyObject , const char , struct __va_list_tag *): Assertion 'callable != NULL' failed.` #142737

Crash report

What happened?

CPython versions tested on:

Operating systems tested on:

Output from running 'python -VV' on the command line:

Linked PRs

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

	open = PyObject_GetAttr(io, &_Py_ID(open));
	for (i = 0; i < npath; i++) {
	v = PyList_GetItem(syspath, i);
	if (v == NULL) {

assertion failure at Objects/call.c:618: PyObject *callmethod(PyThreadState *, PyObject *, const char *, struct __va_list_tag *): Assertion 'callable != NULL' failed. #142737

Description

Crash report

What happened?

CPython versions tested on:

Operating systems tested on:

Output from running 'python -VV' on the command line:

Linked PRs

Activity

johnslavik commented on Dec 15, 2025

ZeroIntensity commented on Dec 15, 2025

johnslavik commented on Dec 15, 2025

ZeroIntensity commented on Dec 15, 2025

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions

assertion failure at Objects/call.c:618: `PyObject callmethod(PyThreadState , PyObject , const char , struct __va_list_tag *): Assertion 'callable != NULL' failed.` #142737