Posted 29 July 2026
In a prior post, Grok help me figure out why I was having so much trouble trying to change my Voron 2.4 printer from ‘dock’ to ‘no_dock’ configuration. Solving this problem exposed a pretty significant flaw in the way that config_switch.py managed the process of changing the printer.cfg file to reflect the new configuration. After getting everything to work, I suggested we generate a pull request to Vin’s Klipper-toolchanger repo to make the config swap process a bit more dependable. This post is intended to document this effort.
We started out by making sure we had all the preparatory work done.
- I copied yet another set of config files to my PC
- 1. Update my clone of Vin-y’s klipper-toolchanger repo on my printer, so all I had to do was update it with:
cd ~/klipper-toolchanger,git pull. Now my local repo is the same as Vin-y’s main branchcd ~/klipper-toolchanger git status # just to see where you are git pull origin main - Created a new branch so we can make our changes without touching the main branch.Just type this one command and show me the result:bash
git checkout -b fix-config-switch-in-place - In VS Code on my PC, I navigated to /home/pi/klipper-toolchanger/klipper/extras/config_switch.py and replaced its contents with the file generated by Grok.
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# Copyright (C) 2024 Chinh Nhan Vo <nhanvo29@proton.me> # Improved 2026 by Frank Paynter / Grok – fix section replacement, marker handling, # and prevent progressive corruption of printer.cfg # # This file may be distributed under the terms of the GNU GPLv3 license. # import os import logging import shutil from datetime import datetime class ConfigSwitch: def __init__(self, config): self.printer = config.get_printer() self.gcode = self.printer.lookup_object('gcode') ## Register Commands self.gcode.register_command('SAVE_CONFIG_MODE', self.cmd_SAVE_CONFIG_MODE, desc=self.cmd_SAVE_CONFIG_MODE_help) self.gcode.register_command('TOGGLE_CONFIG_MODE', self.cmd_TOGGLE_CONFIG_MODE, desc=self.cmd_TOGGLE_CONFIG_MODE_help) # ------------------------------------------------------------------ # Helpers # ------------------------------------------------------------------ def _get_paths(self): home_dir = os.path.expanduser("~") printer_config = os.path.join(home_dir, "printer_data/config/printer.cfg") config_dir = os.path.join(home_dir, "printer_data/config/config") return { "printer": printer_config, "dir": config_dir, "wt": os.path.join(config_dir, "config_wt_dock.cfg"), "no": os.path.join(config_dir, "config_no_dock.cfg"), "temp": os.path.join(config_dir, "printer.temp"), } def _ensure_config_dir(self, config_dir): if not os.path.exists(config_dir): os.makedirs(config_dir, exist_ok=True) def _read_lines(self, path): with open(path, "r") as f: return f.readlines() def _write_lines(self, path, lines): with open(path, "w") as f: f.writelines(lines) def _find_markers(self, lines): """Return (start_idx, end_idx) inclusive, or raise.""" start = end = None for i, line in enumerate(lines): stripped = line.strip() if "#;<" in stripped: if start is not None: raise self.gcode.error("Multiple '#;<' markers found in printer.cfg") start = i if "#;>" in stripped: if end is not None: raise self.gcode.error("Multiple '#;>' markers found in printer.cfg") end = i if start is None or end is None: raise self.gcode.error( "Missing '#;<' or '#;>' marker in printer.cfg – " "the swappable section is not defined" ) if end <= start: raise self.gcode.error("'#;>' appears before '#;<' – markers are inverted") return start, end def _get_current_dock_state(self, lines): for line in lines: if "variable_dock:" in line.strip(): if "True" in line: return True if "False" in line: return False raise self.gcode.error( "Could not find a valid 'variable_dock: True/False' line inside the marked section" ) # ------------------------------------------------------------------ # SAVE_CONFIG_MODE # ------------------------------------------------------------------ cmd_SAVE_CONFIG_MODE_help = "Save the marked session-variable section to the appropriate config_*.cfg" def cmd_SAVE_CONFIG_MODE(self, gcmd): paths = self._get_paths() self._ensure_config_dir(paths["dir"]) lines = self._read_lines(paths["printer"]) start, end = self._find_markers(lines) dock = self._get_current_dock_state(lines[start:end+1]) dest = paths["wt"] if dock else paths["no"] section = lines[start:end+1] # inclusive – keeps both markers self._write_lines(dest, section) name = "config_wt_dock.cfg" if dock else "config_no_dock.cfg" self.gcode.respond_info(f"Session variables (incl. markers) saved to config/{name}") # ------------------------------------------------------------------ # TOGGLE_CONFIG_MODE # ------------------------------------------------------------------ cmd_TOGGLE_CONFIG_MODE_help = "Replace the marked section with the opposite config_*.cfg (in-place)" def cmd_TOGGLE_CONFIG_MODE(self, gcmd): paths = self._get_paths() self._ensure_config_dir(paths["dir"]) lines = self._read_lines(paths["printer"]) start, end = self._find_markers(lines) dock = self._get_current_dock_state(lines[start:end+1]) # Choose the opposite file source = paths["no"] if dock else paths["wt"] if not os.path.exists(source): raise self.gcode.error(f"Missing source file: {source}") new_section = self._read_lines(source) # Sanity-check the incoming section has the markers if not any("#;<" in l for l in new_section) or not any("#;>" in l for l in new_section): raise self.gcode.error( f"{os.path.basename(source)} is missing '#;<' or '#;>' – " "run SAVE_CONFIG_MODE first on a clean printer.cfg" ) # Optional safety backup timestamp = datetime.now().strftime("%Y%m%d_%H%M%S") backup = paths["printer"] + f".bak_{timestamp}" shutil.copy2(paths["printer"], backup) self.gcode.respond_info(f"Backup created: {os.path.basename(backup)}") # Build the new file: everything before start + new section + everything after end new_lines = lines[:start] + new_section + lines[end+1:] self._write_lines(paths["printer"], new_lines) self.gcode.respond_info( f"Toggled to {'no-dock' if dock else 'with-dock'} configuration " f"(section replaced in-place)" ) def load_config(config): return ConfigSwitch(config) |
Then we restarted the printer. Klipper came up cleanly, so that’s a good sign!
After testing the new script with some round-trip ‘TOGGLE_CONFIG_MODE‘ commands, the new script looks like it is performing correctly.
Grok then guided me through the process of updating the local repo:
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pi@mainsailos:~/printer_data $ cd ~/klipper-toolchanger pi@mainsailos:~/klipper-toolchanger $ git status On branch main Your branch is behind 'origin/main' by 31 commits, and can be fast-forwarded. (use "git pull" to update your local branch) nothing to commit, working tree clean pi@mainsailos:~/klipper-toolchanger $ git pull Updating 4082d29..e7be868 Fast-forward klipper/extras/tools_calibrate.py | 44 +++++++++++++------------------------------- macros/homing.cfg | 5 +++-- macros/print_time_default.cfg | 69 +++++++++++++++++++++++++++++++++++++-------------------------------- macros/tool_calibrate.cfg | 25 +++++++++++++++++-------- macros/toolchanger.cfg | 2 +- scripts/misschanger_settings.cfg | 17 ++++++++++------- 6 files changed, 81 insertions(+), 81 deletions(-) pi@mainsailos:~/klipper-toolchanger $ git status On branch main Your branch is up to date with 'origin/main'. nothing to commit, working tree clean pi@mainsailos:~/klipper-toolchanger $ |
Create a new branch to make the changes without changing the ‘main’ branch:
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git checkout -b fix-config-switch-in-place |
Then in VS Code we overwrote the existing klipper-toolchanger / klipper / extras / config_switch.py with the new version (see above), saved the file and then restarted Klipper with “sudo systemctl restart klipper”
Testing:
At the start of the test program, ‘printer.cfg’ contains the ‘no_dock’ configuration. Then I ran SAVE_CONFIG_MODE fro the mainsail console, and got the following output:
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1:02 PM Session variables (incl. markers) saved to config/config_no_dock.cfg 1:02 PM SAVE_CONFIG_MODE |
Most notably, now the ‘config_no_dock.cfg’ file has both the ‘#;<‘ and ‘#;>’ markers – yay!
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#;< # Section Variable marker #--------------------------------------------------------------- #--------------------------------------------------------------- #07/23/26 Updated to include current T0/T1 cfg files [include 251103_T0-Nitehawk-Revo-LDO.cfg] #[include 251103_T1-Nitehawk-Revo-LDO.cfg] #--------------------------------------------------------------- #################################################################################### ## 10/19/25 [gcode_macro _limits] section added ## See 19 October blog update for details #################################################################################### [gcode_macro _limits] variable_effective_min_y: 0.0 #this value gets changed to '120.0' in 'config_wt_dock' gcode: # Empty, just for variables [gcode_macro PRINT_END] # Use PRINT_END for the slicer ending script - please customise for your slicer of choice gcode: # safe anti-stringing move coords {% set th = printer.toolhead %} {% set x_safe = th.position.x + 20 * (1 if th.axis_maximum.x - th.position.x > 20 else -1) %} {% set y_safe = th.position.y + 20 * (1 if th.axis_maximum.y - th.position.y > 20 else -1) %} {% set z_safe = [th.position.z + 2, th.axis_maximum.z]|min %} SAVE_GCODE_STATE NAME=STATE_PRINT_END M400 ; wait for buffer to clear G92 E0 ; zero the extruder G1 E-5.0 F1800 ; retract filament TURN_OFF_HEATERS G90 ; absolute positioning G0 X{x_safe} Y{y_safe} Z{z_safe} F20000 ; move nozzle to remove stringing ;G0 X{th.axis_maximum.x//2} Y{th.axis_maximum.y - 2} F3600 ; park nozzle at rear G0 X{th.axis_maximum.x//2} Y{th.axis_maximum.y - 10} F3600 ; park nozzle at rear 06/17/25 gfp adj to avoid 'clunk' at end #G0 Z25 F3600 #10/17/25 gfp No dock G0 Z100 F3600 #07/27/26 gfp moved 'No dock' extruder end positin higher for easier print-plate removal/replacement M107 ; turn off fan BED_MESH_CLEAR RESTORE_GCODE_STATE NAME=STATE_PRINT_END #--------------------------------------------------------------- #gfp 09/19/25 edited for 300x300 bed [gcode_macro _home] variable_xh: 150.0 variable_yh: 150.0 #Dock NOT installed # Dock is installed: True or False variable_dock: False gcode: #--------------------------------------------------------------- #05/30/25 added gfp [bed_mesh] speed: 120 horizontal_move_z: 5 mesh_min: 30, 35 #07/05/25 gfp: 30 was not enough for Y mesh_max: 275, 250 probe_count: 5, 5 #06/01/25 chg to 5,5 zero_reference_position: 150,150 #for use with stock z endstop. Added 06/01/25 gfp #gfp 09/19/25 moved here per MissChanger setup instructions [quad_gantry_level] #-------------------------------------------------------------------- ## Gantry Corners for 300mm Build ## Uncomment for 300mm build gantry_corners: -60,-10 360,370 ## Probe points points: #Dock NOT installed 50,25 50,225 250,225 250,25 #;> # End of Session Variables section |
To go the other way, we edited the ‘config_wt_dock.cfg’ file to add the closing marker ‘#;>’ to the end of the file, and then ran TOGGLE_CONFIG_MODE again to swap out the ‘no_dock’ “Session Variables” with teh ‘with_dock’ ones and then checked to make sure the Voron would reboot successfully (it did – yay!) and the “session variables” and ‘SAVE_CONFIG’ sections were correct.
Pull Request:
First we committed all the changes (principally the revised ‘config_switch.py’ script) to the local repo:
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cd ~/klipper-toolchanger git status git add klipper/extras/config_switch.py git commit -m "Fix CONFIG_TOGGLE: replace section in-place instead of appending Previously the toggle stripped the marked block and appended the new config at the end of printer.cfg. This caused progressive corruption, lost the SAVE_CONFIG position, and dropped the closing #;> marker. The new implementation: - Strictly replaces only the text between (and including) the #;< / #;> markers - Leaves all other content (including SAVE_CONFIG) untouched and in order - Always writes both markers into the config_*.cfg files - Creates a timestamped backup before every toggle - Adds clear error checking for missing/duplicate markers Tested with multiple dock / no-dock round-trips on a Voron 2.4 + MissChanger." |
Then before we do anything else, we need to fork Vin-y’s klipper-toolchanger repo to my Github account with
- Navigate to Vin-y’s Github klipper-toolchanger repo with: https://github.com/VIN-y/klipper-toolchanger
- Create a fork
- Push the local repo’s ‘fix-config-switch-in-place’ branch to the newly created fork with:
When the push is performed, Github creates a link that can be used for the pull request:
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pi@mainsailos:~/klipper-toolchanger $ git remote add myfork https://github.com/paynterf/klipper-toolchanger.git git push -u myfork fix-config-switch-in-place Enumerating objects: 9, done. Counting objects: 100% (9/9), done. Delta compression using up to 4 threads Compressing objects: 100% (4/4), done. Writing objects: 100% (5/5), 2.45 KiB | 2.45 MiB/s, done. Total 5 (delta 2), reused 0 (delta 0), pack-reused 0 remote: Resolving deltas: 100% (2/2), completed with 2 local objects. remote: remote: Create a pull request for 'fix-config-switch-in-place' on GitHub by visiting: remote: https://github.com/paynterf/klipper-toolchanger/pull/new/fix-config-switch-in-place remote: To https://github.com/paynterf/klipper-toolchanger.git * [new branch] fix-config-switch-in-place -> fix-config-switch-in-place branch 'fix-config-switch-in-place' set up to track 'myfork/fix-config-switch-in-place'. pi@mainsailos:~/klipper-toolchanger $ |
Here’s what the pull request looks like on Github, just before clicking the ‘Create Pull Request button:
And here’s what it looks like after creating the pull request:
It feels good to be able to contribute something of worth to the MISSChanger community, as I am certain that others have run into similar problems with TOGGLE_CONFIG_MODE.
Stay Tuned,
Frank