diff --git a/src/ocrmypdf/exceptions.py b/src/ocrmypdf/exceptions.py
index b56e8a1a..3db7328f 100644
--- a/src/ocrmypdf/exceptions.py
+++ b/src/ocrmypdf/exceptions.py
@@ -35,6 +35,7 @@ class ExitCodeException(Exception):
     message = ""
 
     def __str__(self):
+        """Return a string representation of the exception."""
         super_msg = super().__str__()  # Don't do str(super())
         if self.message:
             return self.message.format(super_msg)
@@ -94,7 +95,7 @@ class EncryptedPdfError(ExitCodeException):
 
     exit_code = ExitCode.encrypted_pdf
     message = dedent(
-        '''\
+        """\
         Input PDF is encrypted. The encryption must be removed to
         perform OCR.
 
@@ -103,7 +104,7 @@ class EncryptedPdfError(ExitCodeException):
 
         You can remove the encryption using
             qpdf --decrypt [--password=[password]] infilename
-        '''
+        """
     )
 
 
diff --git a/src/ocrmypdf/extra_plugins/__init__.py b/src/ocrmypdf/extra_plugins/__init__.py
index 079cf307..abfdfbbb 100644
--- a/src/ocrmypdf/extra_plugins/__init__.py
+++ b/src/ocrmypdf/extra_plugins/__init__.py
@@ -1,3 +1,9 @@
 # SPDX-FileCopyrightText: 2022 James R. Barlow
 #
 # SPDX-License-Identifier: MPL-2.0
+
+"""Extra plugins. These are not automatically inserted when ocrmypdf is run.
+
+You can use these plugins by specifying them on the command line, e.g.:
+ocrmypdf --plugin ocrmypdf.extra_plugins.semfree ...
+"""
diff --git a/tests/__init__.py b/tests/__init__.py
index 7b419d3f..4252e926 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -1,4 +1,6 @@
 # SPDX-FileCopyrightText: 2022 James R. Barlow
 # SPDX-License-Identifier: MPL-2.0
 
+"""Tests."""
+
 from __future__ import annotations