bug#40563: 28.0.50; Narrow to defun in python buffer

[Tomas Nordin <tomasn@posteo.net>]

Hello Buglist

emacs Q

Find file class.py with this content

----------------------------------8<----------------------------------
"""Try narrow to defun on class"""


class A():

    def a1(self):
        pass

    def a2(self):
        pass


class B():

    def b1(self):
        pass

    def b2(self):
        pass
---------------------------------->8----------------------------------

Move point to bol on class A
C-x n d

result:
----------------------------------8<----------------------------------
lass A():

    def a1(self):
        pass

    def a2(self):
        pass
---------------------------------->8----------------------------------

notice the 'c' is gone

C-x n w

Move point to bol on class B

C-x n d

result:
----------------------------------8<----------------------------------
    def b2(self):
        pass
---------------------------------->8----------------------------------

I then noticed that placing point just below the class definition and
then narrow works as expected. But I think the recipe way should work as
well. And even if not, this behavior is confusing.

Best regards
--
Tomas

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5, cairo version 1.16.0)
 of 2020-04-01 built on fliptop
Repository revision: 1276c8e10b000b571a12227ebe9216cc6305ef7f
Repository branch: tomnor
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Dired-Hide-Details mode enabled in current buffer

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS PDUMPER LCMS2
GMP

Important settings:
  value of $LC_TIME: sv_SE.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

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  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
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Memory information:
((conses 16 44956 6005)
 (symbols 48 5991 1)
 (strings 32 15464 1586)
 (string-bytes 1 508063)
 (vectors 16 9265)
 (vector-slots 8 124796 8898)
 (floats 8 19 43)
 (intervals 56 325 4)
 (buffers 1000 12))