Mod the Machine

Problem debugging Python code

When using the latest two versions of the Python extension inside Visual Studio Code, then instead of VS Code showing up when you click "Edit" or "Debug" inside the  "Script and Add-Ins" dialog, another instance of Fusion 360 will come up 😬

Fortunately, you can simply downgrade back to version 2019.9.34911 of the Python extension to solve the problem:
- go to the Extensions tab in VS Code 
- click on the Settings button ⚙ of the Python extension
- select "Install Another Version..."
- select 2019.9.34911

Un-remove Fusion 360 add-in

Inside the "Scripts and Add-Ins" dialog you have the option to "Remove" a given add-in or script. This will not delete the add-in, but will simply mark it to be ignored in the future, and so it won't be listed or loaded anymore:

But how can you bring it back if you changed your mind? 🤔

1) Close Fusion 360 (if it's running)
2) Move the folder of the add-in to a temporary location - maybe place it in the trash? 
3) Start Fusion 360 - it will realize that the add-in does not exist anymore, so it can delete the note about ignoring it
4) Close Fusion 360
5) Move the add-in's folder back where it was before
6) Start Fusion 360 - the add-in will show up in the list again 😀

 

Constrain Sketch Blocks

You can group sketch geometry together by creating a SketchBlockDefinition out of them using the "Create Block" command:

If you have SketchBlock's (instances of SketchBlockDefinition) in your Sketch then through the UI you can constrain them together without creating any additional geometry in the SketchBlock's definition (SketchBlockDefinition) - e.g. using the midpoint of one of the lines of the SketchBlock:

If you try to do the same through the API, Inventor will crash! 😱

You can work around that by creating the constrained SketchPoint inside the SketchBlockDefinition, and use the representation of that point in the Sketch to add further constraints. Each object in the definition will be represented by a sketch object inside the sketch where you placed the SketchBlock. You can find out which object in the sketch is representing a given object from the SketchBlockDefinition by using the SketchBlock.GetObject() function. 
FYI: the first SketchPoint in the SketchBlockDefinition is always the insertion point:

If you wanted to constrain two instances of the same SketchBlockDefinition together by the midpoint of their 3rd and 1st line, then this is how you could do it:

Sub ConstrainBlockLine()
Dim oPartDoc As PartDocument
Dim oSketchLine As SketchLine
Dim oMiddlePoint1 As SketchPoint
Dim oMiddlePoint2 As SketchPoint
Dim oTG As TransientGeometry
Dim oSketch As PlanarSketch
Dim oSketchBlock1 As SketchBlock
Dim oSketchBlock2 As SketchBlock
Dim oSketchBlockDef As SketchBlockDefinition

Set oPartDoc = ThisApplication.ActiveDocument
Set oTG = ThisApplication.TransientGeometry

Set oSketch = oPartDoc.ComponentDefinition.Sketches(1)
Set oSketchBlock1 = oSketch.SketchBlocks.Item(1)
Set oSketchBlock2 = oSketch.SketchBlocks.Item(2)
Set oSketchBlockDef = oSketchBlock1.Definition

'edit Sketch
Call oSketch.Edit
'edit SketchBlock
Call oSketchBlock1.Edit

Dim oMiddlePointNative1 As SketchPoint
Set oMiddlePointNative1 = oSketchBlockDef.SketchPoints.Add(oTG.CreatePoint2d(0, 0), False)

Set oSketchLine = oSketchBlockDef.SketchLines(1)
Call oSketchBlockDef.GeometricConstraints.AddMidpoint(oMiddlePointNative1, oSketchLine)

Dim oMiddlePointNative2 As SketchPoint
Set oMiddlePointNative2 = oSketchBlockDef.SketchPoints.Add(oTG.CreatePoint2d(0, 0), False)

Set oSketchLine = oSketchBlockDef.SketchLines(3)
Call oSketchBlockDef.GeometricConstraints.AddMidpoint(oMiddlePointNative2, oSketchLine)

Call oSketchBlock1.ExitEdit(kExitToPrevious)

Set oMiddlePoint1 = oSketchBlock1.GetObject(oMiddlePointNative1)
Set oMiddlePoint2 = oSketchBlock2.GetObject(oMiddlePointNative2)

Call oSketch.GeometricConstraints.AddCoincident(oMiddlePoint1, oMiddlePoint2)

Call oSketch.ExitEdit

End Sub

Result:

Issues with migrating to Python 3.7.3

As I mentioned it in this blog post, the new version of Python (3.7.3) that Fusion 360 migrated to seems more strict, and is causing some add-ins to fail.

Here are the main issues I've seen pop up:

1) Having an empty code block: if/else, try/except, etc
Code:

try:
except:

Error:

Sorry: IndentationError: expected an indented block (PythonTest.py, line 25)

Solution: remove the whole block or just put a "pass" inside it:

try:
  pass
except:
  pass

2) Referencing a global variable multiple times in the same function using the "global" keyword - even if from different execution paths
Code:

my_global_variable = ""

def run(context):
  if ui:
    global my_global_variable
    my_global_variable = "True"
  else: 
    global my_global_variable
    my_global_variable = "False"

Error:

SyntaxError: name 'my_global_variable' is assigned to before global declaration

Solution: use the "global" references at the beginning of the function 

my_global_variable = ""

def run(context):
  global my_global_variable
  if ui:
    my_global_variable = "True"
  else: 
    my_global_variable = "False"

3) One other issue, which is not necessarily a result of the compiler's strictness, is that you may be relying on packages that are based on an earlier version of Python. If loading those modules is causing errors then you might have to upgrade those packages. It might be done in different ways depending on where you got those packages from. 

Cannot debug my Python add-in

Just wrote an article on how to debug your Python script/add-in

One thing missing from it is about what to do if the compiler runs into problems with the main module (vs an additional module your code is loading).
In that case, checking "Raised Exceptions" in the "Breakpoints" section is not enough 🙁
Your code will fail silently and the debug process won't start

You can work around that by running Python compile on your main module/main Python file to find out what the problem is with it.

Once you started debugging your code from Fusion 360 and ended up in VS Code, you can follow these steps:

1) Open up the Terminal in VS Code (View >> Terminal)

2) Open the .vscode\settings.json file of your add-in - this will have the path to the Python version that Fusion 360 is using

3) Copy the full path set for "python.pythonPath" into the terminal

4) Add "-m py_compile" to the text in the Terminal window

5) Drag&drop your Python file's tab into the Terminal - that will copy/paste the full path of that file in the Terminal

6) Now just hit enter in the Terminal and that should run the Python compiler, which should list the first error the compiler runs into 

Let's compare the error and our Python file:

In this case, the error message is not the clearest, but at least we have something to go on 🙂
Solution to this specific error is here: Issues with migrating to Python 3.7.3