gh-102541: Fix Helper.help("mod") for non-existent mod (#105934)

If the output arg to Helper() is a stream rather than the default None, which means 'page to stdout', the ImportError from pydoc.resolve is currently not caught in pydoc.doc. The same error is caught when output is None.
---------

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

1 files changed, 5 insertions, 1 deletions

diff --git a/Lib/pydoc.py b/Lib/pydoc.py
index d69369d..185f09e 100755
--- a/Lib/pydoc.py
+++ b/Lib/pydoc.py
@@ -1790,7 +1790,11 @@ def doc(thing, title='Python Library Documentation: %s', forceload=0,
                 raise
             print(exc)
     else:
-        output.write(render_doc(thing, title, forceload, plaintext))
+        try:
+            s = render_doc(thing, title, forceload, plaintext)
+        except ImportError as exc:
+            s = str(exc)
+        output.write(s)
 
 def writedoc(thing, forceload=0):
     """Write HTML documentation to a file in the current directory."""