1 files changed, 169 insertions, 0 deletions
diff --git a/Lib/_pyrepl/pager.py b/Lib/_pyrepl/pager.py
new file mode 100644
index 00000000000..ecf5ddc79a5
--- /dev/null
+++ b/Lib/_pyrepl/pager.py
@@ -0,0 +1,169 @@
+from __future__ import annotations
+
+import io
+import os
+import re
+import sys
+
+
+# types
+if False:
+    from typing import Protocol, Any
+    class Pager(Protocol):
+        def __call__(self, text: str, title: str = "") -> None:
+            ...
+
+
+def get_pager() -> Pager:
+    """Decide what method to use for paging through text."""
+    if not hasattr(sys.stdin, "isatty"):
+        return plain_pager
+    if not hasattr(sys.stdout, "isatty"):
+        return plain_pager
+    if not sys.stdin.isatty() or not sys.stdout.isatty():
+        return plain_pager
+    if sys.platform == "emscripten":
+        return plainpager
+    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, title='': tempfile_pager(plain(text), use_pager)
+        elif os.environ.get('TERM') in ('dumb', 'emacs'):
+            return lambda text, title='': pipe_pager(plain(text), use_pager, title)
+        else:
+            return lambda text, title='': pipe_pager(text, use_pager, title)
+    if os.environ.get('TERM') in ('dumb', 'emacs'):
+        return plain_pager
+    if sys.platform == 'win32':
+        return lambda text, title='': tempfilepager(plain(text), 'more <')
+    if hasattr(os, 'system') and os.system('(less) 2>/dev/null') == 0:
+        return lambda text, title='': pipe_pager(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, title='': pipe_pager(text, 'more', title)
+        else:
+            return tty_pager
+    finally:
+        os.unlink(filename)
+
+
+def escape_stdout(text: str) -> str:
+    # Escape non-encodable characters to avoid encoding errors later
+    encoding = getattr(sys.stdout, 'encoding', None) or 'utf-8'
+    return text.encode(encoding, 'backslashreplace').decode(encoding)
+
+
+def escape_less(s: str) -> str:
+    return re.sub(r'([?:.%\\])', r'\\\1', s)
+
+
+def plain(text: str) -> str:
+    """Remove boldface formatting from text."""
+    return re.sub('.\b', '', text)
+
+
+def tty_pager(text: str, title: str = '') -> None:
+    """Page through text on a text terminal."""
+    lines = plain(escape_stdout(text)).split('\n')
+    has_tty = False
+    try:
+        import tty
+        import termios
+        fd = sys.stdin.fileno()
+        old = termios.tcgetattr(fd)
+        tty.setcbreak(fd)
+        getchar = lambda: sys.stdin.read(1)
+        has_tty = True
+    except (ImportError, AttributeError, io.UnsupportedOperation):
+        getchar = lambda: sys.stdin.readline()[:-1][:1]
+
+    try:
+        try:
+            h = int(os.environ.get('LINES', 0))
+        except ValueError:
+            h = 0
+        if h <= 1:
+            h = 25
+        r = inc = h - 1
+        sys.stdout.write('\n'.join(lines[:inc]) + '\n')
+        while lines[r:]:
+            sys.stdout.write('-- more --')
+            sys.stdout.flush()
+            c = getchar()
+
+            if c in ('q', 'Q'):
+                sys.stdout.write('\r          \r')
+                break
+            elif c in ('\r', '\n'):
+                sys.stdout.write('\r          \r' + lines[r] + '\n')
+                r = r + 1
+                continue
+            if c in ('b', 'B', '\x1b'):
+                r = r - inc - inc
+                if r < 0: r = 0
+            sys.stdout.write('\n' + '\n'.join(lines[r:r+inc]) + '\n')
+            r = r + inc
+
+    finally:
+        if has_tty:
+            termios.tcsetattr(fd, termios.TCSAFLUSH, old)
+
+
+def plain_pager(text: str, title: str = '') -> None:
+    """Simply print unformatted text.  This is the ultimate fallback."""
+    sys.stdout.write(plain(escape_stdout(text)))
+
+
+def pipe_pager(text: str, cmd: str, title: str = '') -> None:
+    """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.'
+        '.'
+        '?e (END):?pB %pB\\%..'
+        ' (press h for help or q to quit)')
+    env['LESS'] = '-RmPm{0}$PM{0}$'.format(prompt_string)
+    proc = subprocess.Popen(cmd, shell=True, stdin=subprocess.PIPE,
+                            errors='backslashreplace', env=env)
+    assert proc.stdin is not None
+    try:
+        with proc.stdin as pipe:
+            try:
+                pipe.write(text)
+            except KeyboardInterrupt:
+                # We've hereby abandoned whatever text hasn't been written,
+                # but the pager is still in control of the terminal.
+                pass
+    except OSError:
+        pass # Ignore broken pipes caused by quitting the pager program.
+    while True:
+        try:
+            proc.wait()
+            break
+        except KeyboardInterrupt:
+            # Ignore ctl-c like the pager itself does.  Otherwise the pager is
+            # left running and the terminal is in raw mode and unusable.
+            pass
+
+
+def tempfile_pager(text: str, cmd: str, title: str = '') -> None:
+    """Page through text by invoking a program on a temporary file."""
+    import tempfile
+    with tempfile.TemporaryDirectory() as tempdir:
+        filename = os.path.join(tempdir, 'pydoc.out')
+        with open(filename, 'w', errors='backslashreplace',
+                  encoding=os.device_encoding(0) if
+                  sys.platform == 'win32' else None
+                  ) as file:
+            file.write(text)
+        os.system(cmd + ' "' + filename + '"')