Issue #15767: Introduce ModuleNotFoundError, a subclass of

ImportError.

The exception is raised by import when a module could not be found.
Technically this is defined as no viable loader could be found for the
specified module. This includes ``from ... import`` statements so that
the module usage is consistent for all situations where import
couldn't find what was requested.

This should allow for the common idiom of::

  try:
    import something
  except ImportError:
    pass

to be updated to using ModuleNotFoundError and not accidentally mask
ImportError messages that should propagate (e.g. issues with a
loader).

This work was driven by the fact that the ``from ... import``
statement needed to be able to tell the difference between an
ImportError that simply couldn't find a module (and thus silence the
exception so that ceval can raise it) and an ImportError that
represented an actual problem.

1 files changed, 1 insertions, 1 deletions

diff --git a/Lib/test/test_pydoc.py b/Lib/test/test_pydoc.py
index 399f818..95ef115 100644
--- a/Lib/test/test_pydoc.py
+++ b/Lib/test/test_pydoc.py
@@ -206,7 +206,7 @@ expected_html_data_docstrings = tuple(s.replace(' ', ' ')
 missing_pattern = "no Python documentation found for '%s'"
 
 # output pattern for module with bad imports
-badimport_pattern = "problem in %s - ImportError: No module named %r"
+badimport_pattern = "problem in %s - ModuleNotFoundError: No module named %r"
 
 def run_pydoc(module_name, *args, **env):
     """