bpo-37755: Use configured output in pydoc instead of pager (GH-15105)

If the Helper() class was initialized with an output, the topics, keywords
and symbols help still use the pager instead of the output.
Change the behavior so  the output is used if available while keeping the
previous behavior if no output was configured.

Lib/pydoc.py

@@ -2034,7 +2034,7 @@ has the same effect as typing a particular string at the help> prompt.
             elif request in self.symbols: self.showsymbol(request)
             elif request in ['True', 'False', 'None']:
                 # special case these keywords since they are objects too
-                doc(eval(request), 'Help on %s:', is_cli=is_cli)
+                doc(eval(request), 'Help on %s:', output=self._output, is_cli=is_cli)
             elif request in self.keywords: self.showtopic(request)
             elif request in self.topics: self.showtopic(request)
             elif request: doc(request, 'Help on %s:', output=self._output, is_cli=is_cli)
@@ -2127,7 +2127,11 @@ module "pydoc_data.topics" could not be found.
             text = 'Related help topics: ' + ', '.join(xrefs.split()) + '\n'
             wrapped_text = textwrap.wrap(text, 72)
             doc += '\n%s\n' % '\n'.join(wrapped_text)
+
+        if self._output is None:
             pager(doc, f'Help on {topic!s}')
+        else:
+            self.output.write(doc)
 
     def _gettopic(self, topic, more_xrefs=''):
         """Return unbuffered tuple of (topic, xrefs).

Lib/test/test_pydoc/test_pydoc.py

@@ -17,6 +17,7 @@ import time
 import types
 import typing
 import unittest
+import unittest.mock
 import urllib.parse
 import xml.etree
 import xml.etree.ElementTree
@@ -658,16 +659,13 @@ class PydocDocTest(unittest.TestCase):
 
     @unittest.skipIf(hasattr(sys, 'gettrace') and sys.gettrace(),
                      'trace function introduces __locals__ unexpectedly')
+    @unittest.mock.patch('pydoc.pager')
     @requires_docstrings
-    def test_help_output_redirect(self):
+    def test_help_output_redirect(self, pager_mock):
         # issue 940286, if output is set in Helper, then all output from
         # Helper.help should be redirected
-        getpager_old = pydoc.getpager
-        getpager_new = lambda: (lambda x: x)
         self.maxDiff = None
 
-        buf = StringIO()
-        helper = pydoc.Helper(output=buf)
         unused, doc_loc = get_pydoc_text(pydoc_mod)
         module = "test.test_pydoc.pydoc_mod"
         help_header = """
@@ -677,10 +675,10 @@ class PydocDocTest(unittest.TestCase):
         help_header = textwrap.dedent(help_header)
         expected_help_pattern = help_header + expected_text_pattern
 
-        pydoc.getpager = getpager_new
-        try:
         with captured_output('stdout') as output, \
-                 captured_output('stderr') as err:
+             captured_output('stderr') as err, \
+             StringIO() as buf:
+            helper = pydoc.Helper(output=buf)
             helper.help(module)
             result = buf.getvalue().strip()
             expected_text = expected_help_pattern % (
@@ -690,8 +688,99 @@ class PydocDocTest(unittest.TestCase):
             self.assertEqual('', output.getvalue())
             self.assertEqual('', err.getvalue())
             self.assertEqual(expected_text, result)
-        finally:
-            pydoc.getpager = getpager_old
+
+        pager_mock.assert_not_called()
+
+    @unittest.skipIf(hasattr(sys, 'gettrace') and sys.gettrace(),
+                     'trace function introduces __locals__ unexpectedly')
+    @requires_docstrings
+    @unittest.mock.patch('pydoc.pager')
+    def test_help_output_redirect_various_requests(self, pager_mock):
+        # issue 940286, if output is set in Helper, then all output from
+        # Helper.help should be redirected
+
+        def run_pydoc_for_request(request, expected_text_part):
+            """Helper function to run pydoc with its output redirected"""
+            with captured_output('stdout') as output, \
+                 captured_output('stderr') as err, \
+                 StringIO() as buf:
+                helper = pydoc.Helper(output=buf)
+                helper.help(request)
+                result = buf.getvalue().strip()
+                self.assertEqual('', output.getvalue(), msg=f'failed on request "{request}"')
+                self.assertEqual('', err.getvalue(), msg=f'failed on request "{request}"')
+                self.assertIn(expected_text_part, result, msg=f'failed on request "{request}"')
+                pager_mock.assert_not_called()
+
+        self.maxDiff = None
+
+        # test for "keywords"
+        run_pydoc_for_request('keywords', 'Here is a list of the Python keywords.')
+        # test for "symbols"
+        run_pydoc_for_request('symbols', 'Here is a list of the punctuation symbols')
+        # test for "topics"
+        run_pydoc_for_request('topics', 'Here is a list of available topics.')
+        # test for "modules" skipped, see test_modules()
+        # test for symbol "%"
+        run_pydoc_for_request('%', 'The power operator')
+        # test for special True, False, None keywords
+        run_pydoc_for_request('True', 'class bool(int)')
+        run_pydoc_for_request('False', 'class bool(int)')
+        run_pydoc_for_request('None', 'class NoneType(object)')
+        # test for keyword "assert"
+        run_pydoc_for_request('assert', 'The "assert" statement')
+        # test for topic "TYPES"
+        run_pydoc_for_request('TYPES', 'The standard type hierarchy')
+        # test for "pydoc.Helper.help"
+        run_pydoc_for_request('pydoc.Helper.help', 'Help on function help in pydoc.Helper:')
+        # test for pydoc.Helper.help
+        run_pydoc_for_request(pydoc.Helper.help, 'Help on function help in module pydoc:')
+        # test for pydoc.Helper() instance skipped because it is always meant to be interactive
+
+    def test_showtopic(self):
+        with captured_stdout() as showtopic_io:
+            helper = pydoc.Helper()
+            helper.showtopic('with')
+        helptext = showtopic_io.getvalue()
+        self.assertIn('The "with" statement', helptext)
+
+    def test_fail_showtopic(self):
+        with captured_stdout() as showtopic_io:
+            helper = pydoc.Helper()
+            helper.showtopic('abd')
+            expected = "no documentation found for 'abd'"
+            self.assertEqual(expected, showtopic_io.getvalue().strip())
+
+    @unittest.mock.patch('pydoc.pager')
+    def test_fail_showtopic_output_redirect(self, pager_mock):
+        with StringIO() as buf:
+            helper = pydoc.Helper(output=buf)
+            helper.showtopic("abd")
+            expected = "no documentation found for 'abd'"
+            self.assertEqual(expected, buf.getvalue().strip())
+
+        pager_mock.assert_not_called()
+
+    @unittest.skipIf(hasattr(sys, 'gettrace') and sys.gettrace(),
+                     'trace function introduces __locals__ unexpectedly')
+    @requires_docstrings
+    @unittest.mock.patch('pydoc.pager')
+    def test_showtopic_output_redirect(self, pager_mock):
+        # issue 940286, if output is set in Helper, then all output from
+        # Helper.showtopic should be redirected
+        self.maxDiff = None
+
+        with captured_output('stdout') as output, \
+             captured_output('stderr') as err, \
+             StringIO() as buf:
+            helper = pydoc.Helper(output=buf)
+            helper.showtopic('with')
+            result = buf.getvalue().strip()
+            self.assertEqual('', output.getvalue())
+            self.assertEqual('', err.getvalue())
+            self.assertIn('The "with" statement', result)
+
+        pager_mock.assert_not_called()
 
     def test_lambda_with_return_annotation(self):
         func = lambda a, b, c: 1

Misc/NEWS.d/next/Library/2024-06-02-13-35-11.gh-issue-81936.ETeW9x.rst

@@ -0,0 +1,3 @@
+:meth:`!help` and :meth:`!showtopic` methods now respect a
+configured *output* argument to :class:`!pydoc.Helper` and not use the
+pager in such cases. Patch by Enrico Tröger.