gh-65824: Add "Help on ..." to the "less" prompt in pydoc (GH-116183)

Author: serhiy-storchaka

Lib/pydoc.py

@@ -1637,11 +1637,11 @@ def bold(self, text):
 
 # --------------------------------------------------------- user interfaces
 
-def pager(text):
+def pager(text, title=''):
  """The first time this is called, determine what kind of pager to use."""
  global pager
  pager = getpager()
- pager(text)
+ pager(text, title)
 
 def getpager():
  """Decide what method to use for paging through text."""
@@ -1656,24 +1656,24 @@ def getpager():
  use_pager = os.environ.get('MANPAGER') or os.environ.get('PAGER')
  if use_pager:
  if sys.platform == 'win32': # pipes completely broken in Windows
- return lambda text: tempfilepager(plain(text), use_pager)
+ return lambda text, title='': tempfilepager(plain(text), use_pager)
  elif os.environ.get('TERM') in ('dumb', 'emacs'):
- return lambda text: pipepager(plain(text), use_pager)
+ return lambda text, title='': pipepager(plain(text), use_pager, title)
  else:
- return lambda text: pipepager(text, use_pager)
+ return lambda text, title='': pipepager(text, use_pager, title)
  if os.environ.get('TERM') in ('dumb', 'emacs'):
  return plainpager
  if sys.platform == 'win32':
- return lambda text: tempfilepager(plain(text), 'more <')
+ return lambda text, title='': tempfilepager(plain(text), 'more <')
  if hasattr(os, 'system') and os.system('(less) 2>/dev/null') == 0:
- return lambda text: pipepager(text, 'less')
+ return lambda text, title='': pipepager(text, 'less', title)
 
  import tempfile
  (fd, filename) = tempfile.mkstemp()
  os.close(fd)
  try:
  if hasattr(os, 'system') and os.system('more "%s"' % filename) == 0:
- return lambda text: pipepager(text, 'more')
+ return lambda text, title='': pipepager(text, 'more', title)
  else:
  return ttypager
  finally:
@@ -1683,12 +1683,18 @@ def plain(text):
  """Remove boldface formatting from text."""
  return re.sub('.\b', '', text)
 
-def pipepager(text, cmd):
+def escape_less(s):
+ return re.sub(r'([?:.%\\])', r'\\\1', s)
+
+def pipepager(text, cmd, title=''):
  """Page through text by feeding it to another program."""
  import subprocess
  env = os.environ.copy()
+ if title:
+ title += ' '
+ esc_title = escape_less(title)
  prompt_string = (
- ' '
+ f' {esc_title}' +
  '?ltline %lt?L/%L.'
  ':byte %bB?s/%s.'
  '.'
@@ -1716,7 +1722,7 @@ def pipepager(text, cmd):
  # left running and the terminal is in raw mode and unusable.
  pass
 
-def tempfilepager(text, cmd):
+def tempfilepager(text, cmd, title=''):
  """Page through text by invoking a program on a temporary file."""
  import tempfile
  with tempfile.TemporaryDirectory() as tempdir:
@@ -1733,7 +1739,7 @@ def _escape_stdout(text):
  encoding = getattr(sys.stdout, 'encoding', None) or 'utf-8'
  return text.encode(encoding, 'backslashreplace').decode(encoding)
 
-def ttypager(text):
+def ttypager(text, title=''):
  """Page through text on a text terminal."""
  lines = plain(_escape_stdout(text)).split('\n')
  try:
@@ -1777,7 +1783,7 @@ def ttypager(text):
  if tty:
  tty.tcsetattr(fd, tty.TCSAFLUSH, old)
 
-def plainpager(text):
+def plainpager(text, title=''):
  """Simply print unformatted text. This is the ultimate fallback."""
  sys.stdout.write(plain(_escape_stdout(text)))
 
@@ -1879,7 +1885,8 @@ def doc(thing, title='Python Library Documentation: %s', forceload=0,
  """Display text documentation, given an object or a path to an object."""
  if output is None:
  try:
- pager(render_doc(thing, title, forceload))
+ what = thing if isinstance(thing, str) else type(thing).__name__
+ pager(render_doc(thing, title, forceload), f'Help on {what!s}')
  except ImportError as exc:
  if is_cli:
  raise
@@ -2253,7 +2260,7 @@ def showtopic(self, topic, more_xrefs=''):
  text = 'Related help topics: ' + ', '.join(xrefs.split()) + '\n'
  wrapped_text = textwrap.wrap(text, 72)
  doc += '\n%s\n' % '\n'.join(wrapped_text)
- pager(doc)
+ pager(doc, f'Help on {topic!s}')
 
  def _gettopic(self, topic, more_xrefs=''):
  """Return unbuffered tuple of (topic, xrefs).