Setting objects into edit mode often seems to fail in python script

Question

I am only just starting to learn/use python in blender. I have the following script

import bpy

for obj in bpy.data.objects:

    if obj.name[0:4] == "Text" and obj.type == "MESH":

        bpy.context.scene.objects.active = obj
        bpy.ops.object.mode_set(mode = 'EDIT')
        print(bpy.context.mode)


        #bpy.ops.mesh.select_all(action = 'SELECT')
        #print(bpy.ops.mesh.remove_doubles(0.0001))
        bpy.ops.object.mode_set(mode = 'OBJECT')

I am trying to work out why I keep getting a context error for bpy.ops.mesh.select_all so I added the print(bpy.context.mode) line and commented out the line that was failing (plus the next line which takes action)

what I get in the console (this script is being run from the console rather than run in place) is a mixture of 'OBJECT' and 'EDIT_MESH' outputs.. suggesting that mode_set is failing a lot of the time.

What am I doing wrong?

I am using blender 2.68a on Windows 7.

Edit I discovered the actual cause of my issue (hinted at by Adhi's edit) and wanted to add it to my post so that others can take something away from this - the objects that were not being switched into edit mode were on another layer. Once I made all layers active my script was able to switch all objects into edit mode. So basically an object in an unselected layer cannot be set into edit mode.

I am also grateful for the other help and suggestions, they have been useful to help me learn python scripting within blender which is something I would love to use more extensively.

Answer 1

As mentioned by dimus, your problem is solved by adding keyword to the mesh.remove_doubles operator's first argument, meant as threshold property value. With that little bug fixed, your script works properly.

What causes the error is that, keyword arguments are used to set operator properties, and positional arguments to set how the operator is called (further explained in the API docs). By not using a keyword for the first argument, you're turning it into a positional argument, thus interpreted as operator execution context which is an error.

EDIT: Another possible error is iterating over bpy.data.objects, which comprises of all objects in every scene in a file. The script is bound to fail if there's more than one scene in a file containing a MESH object, because it'll try to make object from a different scene the active object of current scene which is contextually incorrect. You should iterate over bpy.context.scene.objects instead.

Here's the amended code, can't see any other bug:

import bpy

scene = bpy.context.scene
scene.layers = [True] * 20 # Show all layers

for obj in scene.objects:
    if obj.type == 'MESH':
        scene.objects.active = obj

        bpy.ops.object.mode_set(mode='EDIT')
        bpy.ops.mesh.remove_doubles(threshold=0.0001)
        bpy.ops.object.mode_set(mode='OBJECT')

Answer 2

I, too, have had issues in the past using the mesh select_all operator from within Edit mode. As an alternative, try looping through all of the vertices and setting their select property to True. Then, switch into Edit mode before doing the Remove Doubles operator. Your code should look something like this:

for obj in bpy.data.objects:

    if obj.name[0:4] == "Text" and obj.type == 'MESH':

        bpy.context.scene.objects.active = obj
        for vert in obj.vertices:
            vert.select = True
        bpy.ops.object.mode_set(mode='EDIT')
        bpy.ops.mesh.remove_doubles(threshold=0.0001)
        bpy.ops.object.mode_set(mode='OBJECT')

Answer 3

I came across this subject and want to post my solution, removing doubles of object with given objectname :

def myremovedoubles(objectname, mergedist):
    obj = None
    try:
        obj = bpy.data.objects[objectname]
    except ( RuntimeError ):
        pass  
    if (obj != None): 
        try:
            bpy.ops.object.mode_set(mode='OBJECT')
            bpy.ops.object.select_all(action='DESELECT')
            bpy.data.objects[objectname].select = True            
            scene.objects.active = obj
            bpy.ops.object.mode_set(mode='EDIT')
            bpy.ops.mesh.remove_doubles(mergedist=mergedist)
            bpy.ops.object.mode_set(mode='OBJECT')
            return True
        except ( RuntimeError ):
            pass  
    return False   

this function will return True if executed without RuntimeError, meaning the remove_doubles function was executed

it doesn't crash when the object doesn't exist it sets the object as the only active (and selected) it switches between modes, assuming mode='OBJECT' is the default