Crash: MRO inference failure with patched inherited class conditionally assigned to original module

[AA-Turner]

Consider the following:

from pdb import Pdb as StdlibPdb

class Pdb(StdlibPdb):
    ...

class PatchedPdb(Pdb):
    ...

if __name__ == '__main__':
    import pdb
    pdb.Pdb = PatchedPdb
    pdb.main()

This crashes, I presume due to bad circular inference with the __name__ == '__main__' block. Removing that section leads to no crash.

This is a simplified reproducer, the original sketch code is below. Note IPython has a long Pdb inheritance, with one of the modules containing a __main__ block as in the reproducer above, so sadly it's not feasible to change/remove that section.

from IPython.terminal.debugger import TerminalPdb

class Spam(TerminalPdb):
    ...

Command used

pylint bug.py

Pylint output

Traceback (most recent call last):
  File ".../site-packages/pylint/lint/pylinter.py", line 821, in _lint_file
    check_astroid_module(module)
    ~~~~~~~~~~~~~~~~~~~~^^^^^^^^
  File ".../site-packages/pylint/lint/pylinter.py", line 1053, in check_astroid_module
    retval = self._check_astroid_module(
        ast_node, walker, rawcheckers, tokencheckers
    )
  File ".../site-packages/pylint/lint/pylinter.py", line 1105, in _check_astroid_module
    walker.walk(node)
    ~~~~~~~~~~~^^^^^^
  File ".../site-packages/pylint/utils/ast_walker.py", line 90, in walk
    self.walk(child)
    ~~~~~~~~~^^^^^^^
  File ".../site-packages/pylint/utils/ast_walker.py", line 87, in walk
    callback(astroid)
    ~~~~~~~~^^^^^^^^^
  File ".../site-packages/pylint/checkers/classes/class_checker.py", line 879, in visit_classdef
    self._check_bases_classes(node)
    ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File ".../site-packages/pylint/checkers/classes/class_checker.py", line 2186, in _check_bases_classes
    unimplemented_abstract_methods(node, is_abstract).items(),
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/pylint/checkers/utils.py", line 954, in unimplemented_abstract_methods
    mro = reversed(node.mro())
                   ~~~~~~~~^^
  File ".../site-packages/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2863, in mro
    return self._compute_mro(context=context)
           ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File ".../site-packages/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2847, in _compute_mro
    mro = base._compute_mro(context=context)
  File ".../site-packages/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2847, in _compute_mro
    mro = base._compute_mro(context=context)
  File ".../site-packages/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2847, in _compute_mro
    mro = base._compute_mro(context=context)
  [Previous line repeated 979 more times]
  File ".../site-packages/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2841, in _compute_mro
    inferred_bases = list(self._inferred_bases(context=context))
  File ".../site-packages/astroid/nodes/scoped_nodes/scoped_nodes.py", line 2825, in _inferred_bases
    baseobj = _infer_last(stmt, context)
  File ".../site-packages/astroid/nodes/scoped_nodes/scoped_nodes.py", line 181, in _infer_last
    for b in arg.infer(context=context.clone()):
                               ~~~~~~~~~~~~~^^
  File ".../site-packages/astroid/context.py", line 131, in clone
    clone = InferenceContext(self.path.copy(), nodes_inferred=self._nodes_inferred)
RecursionError: maximum recursion depth exceeded

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File ".../site-packages/pylint/lint/pylinter.py", line 784, in _lint_files
    self._lint_file(fileitem, module, check_astroid_module)
    ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../site-packages/pylint/lint/pylinter.py", line 823, in _lint_file
    raise astroid.AstroidError from e
astroid.exceptions.AstroidError

Expected behavior

No crash.

Pylint version

pylint 4.0.4
astroid 4.0.3
Python 3.14.2 (main, Dec  5 2025, 16:49:16) [Clang 17.0.0 (clang-1700.4.4.1)]

OS / Environment

darwin (Darwin)

Additional dependencies

None.