Python script to insert gcode commands before a layer

From time to time I need to insert a pause in gcode to change filament. It's a nuisance to manually edit gcode and have to count layers or search for "g1 z". So I wrote a simple python script to automate this and other similar things (e.g., inserting a temperature change). [Here](https://github.com/arpruss/miscellaneous-scad/blob/master/scripts/insert.py) it is (click on "Raw" to download).

USE AT YOUR OWN RISK.

You should first edit the script to change the parking command for pauses. I set X to -12, which should work for my DaVinci 1.0a (Repetier) printer.

The script is designed for gcode produced by Slic3r and my Repetier-based DaVinci 1.0a. You should examine the output the first few times yourself to make sure that you are happy with it and it works with your slicer/printer and isn't confused by preambles in detecting layers.


Here is how to run it:

python insert.py filename.gcode layerspec layercommands layerspec layercommands ...

The layers must be given in order, lowest to highest, and are specified by the `layerspec`s, which can be:

* `zN` : z-coordinate rises to `N` millimeters or higher (also, can say: `Nmm`)
* `lN`: layer number `N` (first layer is number 1; also, can omit the `l` and just give an integer)

The `layercommands` can be:

* `tN`: set extruder temperature to N degrees
* `"pPause message"`: park, print message, pause (`M25`; this is the SD-card pause command), and return to xyz coordinates
* `"ARBITRARY GCODE`" (multiple lines can be separated by colons; capitalization is strongly recommended not to be confused with lowercase `insert.py` commands)

Note that if you're not using an SD card to feed the file, the `M25` pause may not be what you want, and you may want to do `"@pause message"` instead (using the ARBITRARY GCODE option).

There is no support for checksums in the gcode file.