refactor: prepare the interactive shell in its own module

The prompt-hook step (#41) pushed linux.py past its line count in the
quality baseline. The three steps that make netmiko's fresh shell fit to
read - history off, prompt hooks off, no line wrap - and the prompt
pattern move to napalm_linux/_shell.py, under strict mypy. linux.py
shrinks below where it was; the baseline follows.

napalm_linux/_shell.py

@@ -0,0 +1,54 @@
+"""The interactive shell netmiko opens, made fit to be read before the first command."""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+logger = logging.getLogger(__name__)
+
+#: The end of a command's output when nothing better is known: a line that looks
+#: like a shell prompt.
+PROMPT_RE = r"[#$\>]\s*$"
+
+#: Sent before anything else in the interactive session (NetOrk/netork#1039):
+#: the shell writes no history file and records nothing more. The leading space
+#: keeps this line itself out of a history under ``HISTCONTROL=ignorespace``;
+#: a shell without ``set -o history`` (dash) only complains, to /dev/null.
+HISTORY_OFF = " unset HISTFILE; set +o history 2>/dev/null; true"
+
+#: Sent right after ``HISTORY_OFF`` (#41): systemd 258's
+#: ``/etc/profile.d/80-systemd-osc-context.sh`` wraps every command in OSC 3008
+#: sequences from ``PS0`` and ``PROMPT_COMMAND``, each with a fresh UUID. It appends
+#: to ``PROMPT_COMMAND`` as an array, so only ``unset`` removes its hook.
+PROMPT_HOOKS_OFF = " unset PS0 PROMPT_COMMAND; true"
+
+#: Keeps the PTY from wrapping long output lines (e.g. docker JSON).
+NO_LINE_WRAP = "stty cols 10000 2>/dev/null || true"
+
+
+def prepare_shell(device: Any, hostname: str) -> None:
+    """Make netmiko's fresh shell *device* fit to read, one step at a time.
+
+    A step the shell refuses is logged and skipped: none of them is worth
+    failing the connection for.
+    """
+    # No history before anything else is typed (NetOrk/netork#1039).
+    try:
+        device.send_command(HISTORY_OFF, expect_string=PROMPT_RE)
+    except Exception:
+        logger.debug("Could not switch the shell history off on %s", hostname, exc_info=True)
+
+    # No systemd OSC 3008 context around every command (#41). netmiko learned
+    # the prompt with those sequences in front, and a prompt carrying a fresh
+    # UUID never matches again, so it reads the prompt anew once they are gone.
+    try:
+        device.send_command(PROMPT_HOOKS_OFF, expect_string=PROMPT_RE)
+        device.set_base_prompt()
+    except Exception:
+        logger.debug("Could not switch the prompt hooks off on %s", hostname, exc_info=True)
+
+    try:
+        device.send_command(NO_LINE_WRAP, expect_string=PROMPT_RE)
+    except Exception:
+        logger.debug("%s: ignored", hostname, exc_info=True)

napalm_linux/linux.py

@@ -74,6 +74,9 @@ from netmiko.exceptions import (
     NetmikoTimeoutException,
 )
 
+from napalm_linux._shell import PROMPT_RE as _PROMPT_RE
+from napalm_linux._shell import prepare_shell
+
 logger = logging.getLogger("napalm_linux")
 
 # Package managers in detection order
@@ -86,9 +89,6 @@ _RC_MARKER = "__NETORK_RC="
 _RC_MARKER_RE = re.compile(rf"^{_RC_MARKER}(\d+)\s*$", re.MULTILINE)
 
 
-#: The end of a command's output when nothing better is known: a line that looks
-#: like a shell prompt.
-_PROMPT_RE = r"[#$\>]\s*$"
 #: A command ending in ``echo __NAME=$?`` reports its exit status on a line of its
 #: own: ``_RC_MARKER`` here, ``__APT_RC=`` and ``__SVC_RC=`` in napalm-device-types.
 _STATUS_ECHO_RE = re.compile(r"echo\s+(__[A-Z_]+=)\$\?")
@@ -159,18 +159,6 @@ _PRIVILEGED_STDIN = (
     "mktemp, cat) and have root install that file."
 )
 
-#: Sent before anything else in the interactive session (NetOrk/netork#1039):
-#: the shell writes no history file and records nothing more. The leading space
-#: keeps this line itself out of a history under ``HISTCONTROL=ignorespace``;
-#: a shell without ``set -o history`` (dash) only complains, to /dev/null.
-_HISTORY_OFF = " unset HISTFILE; set +o history 2>/dev/null; true"
-
-#: Sent right after ``_HISTORY_OFF`` (#41): systemd 258's
-#: ``/etc/profile.d/80-systemd-osc-context.sh`` wraps every command in OSC 3008
-#: sequences from ``PS0`` and ``PROMPT_COMMAND``, each with a fresh UUID. It appends
-#: to ``PROMPT_COMMAND`` as an array, so only ``unset`` removes its hook.
-_PROMPT_HOOKS_OFF = " unset PS0 PROMPT_COMMAND; true"
-
 #: First in every script ``_sudo`` runs: a sudo that does not prompt (NOPASSWD,
 #: a cached timestamp) leaves the password on stdin, and nothing may read it.
 _NO_STDIN = "exec </dev/null; "
@@ -419,32 +407,7 @@ class LinuxDriver(
             raise ConnectionException(str(exc)) from exc
         self._host_key.observe(self._device.remote_conn_pre.get_transport())
 
-        # No history before anything else is typed (NetOrk/netork#1039).
-        try:
-            self._device.send_command(_HISTORY_OFF, expect_string=_PROMPT_RE)
-        except Exception:
-            logger.debug(
-                "Could not switch the shell history off on %s", self.hostname, exc_info=True
-            )
-
-        # No systemd OSC 3008 context around every command (#41). netmiko learned
-        # the prompt with those sequences in front, and a prompt carrying a fresh
-        # UUID never matches again, so it reads the prompt anew once they are gone.
-        try:
-            self._device.send_command(_PROMPT_HOOKS_OFF, expect_string=_PROMPT_RE)
-            self._device.set_base_prompt()
-        except Exception:
-            logger.debug(
-                "Could not switch the prompt hooks off on %s", self.hostname, exc_info=True
-            )
-
-        # Prevent PTY from wrapping long output lines (e.g. docker JSON).
-        try:
-            self._device.send_command(
-                "stty cols 10000 2>/dev/null || true", expect_string=r"[#$>]\s*$"
-            )
-        except Exception:
-            logger.debug("%s: ignored", self.hostname, exc_info=True)
+        prepare_shell(self._device, self.hostname)
 
         self._pkg_manager = self._forced_pkg_manager or self._detect_pkg_manager()
         logger.debug("Connected to %s, pkg_manager=%s", self.hostname, self._pkg_manager)

tests/quality_baseline.json

@@ -22,7 +22,7 @@
   "napalm_linux.linux"
  ],
  "python_file_lines": {
-  "napalm_linux/linux.py": 2307
+  "napalm_linux/linux.py": 2288
  },
  "untyped_public": []
 }

tests/test_sudo_off_the_command_line.py

@@ -21,7 +21,7 @@ from unittest.mock import MagicMock, patch
 import pytest
 
 from napalm_linux import LinuxDriver
-from napalm_linux.linux import _HISTORY_OFF
+from napalm_linux._shell import HISTORY_OFF as _HISTORY_OFF
 
 _PW = "s3cr3t 'q' $x"
 

tests/test_systemd_osc_context.py

@@ -11,7 +11,8 @@ characters and netOrk could not store the poll.
 
 from unittest.mock import MagicMock, patch
 
-from napalm_linux.linux import _HISTORY_OFF, _PROMPT_HOOKS_OFF, LinuxDriver
+from napalm_linux._shell import HISTORY_OFF, PROMPT_HOOKS_OFF
+from napalm_linux.linux import LinuxDriver
 
 #: What ``cat /etc/os-release | grep PRETTY_NAME ...`` returned through netmiko on
 #: an Ubuntu 26.04.1 host (2026-10-23), the prompt line already gone.
@@ -39,13 +40,13 @@ class TestPromptHooksOff:
         _opened(device)
 
         sent = [c.args[0] for c in device.send_command.call_args_list]
-        assert sent[:2] == [_HISTORY_OFF, _PROMPT_HOOKS_OFF]
+        assert sent[:2] == [HISTORY_OFF, PROMPT_HOOKS_OFF]
 
     def test_it_unsets_both_hooks_including_an_array_prompt_command(self):
         # The script appends to PROMPT_COMMAND as an array; assigning the empty
         # string would only clear element 0 and leave systemd's hook running.
-        assert _PROMPT_HOOKS_OFF.startswith(" ")
-        assert "unset PS0 PROMPT_COMMAND" in _PROMPT_HOOKS_OFF
+        assert PROMPT_HOOKS_OFF.startswith(" ")
+        assert "unset PS0 PROMPT_COMMAND" in PROMPT_HOOKS_OFF
 
     def test_the_prompt_is_read_again_once_the_hooks_are_gone(self):
         # netmiko learned the prompt with the sequences in front of it; a prompt
@@ -56,7 +57,7 @@ class TestPromptHooksOff:
         _opened(device)
 
         calls = [(c[0], c.args[0] if c.args else None) for c in device.mock_calls]
-        hooks_off = calls.index(("send_command", _PROMPT_HOOKS_OFF))
+        hooks_off = calls.index(("send_command", PROMPT_HOOKS_OFF))
         assert "set_base_prompt" in [name for name, _ in calls[hooks_off + 1 :]]
 
     def test_a_shell_that_refuses_it_does_not_stop_the_connection(self):