How to make this script to quickly set specific weights?

Question

I have an idea how to get a faster workflow when assigning weights in edit mode, and would like to know how hard this would be to make in python as an addon:

Before: I'm manually setting weights using this method:

1. Select one or more vertices
2. Select a vertex group
3. Choose a weight, by entering 0.2 and pressing enter
4. Click Assign

If I'm not happy with it, repeat 3-4 until I'm happy. This can be quite cumbersome and a lot of clicking and typing.

After: With my addon, it would be one less step, like this:

1. Select one or more vertices
2. Select a vertex group
3. Click 20 - And 0.2 is assigned in one click

If I'm not happy with it, I just click another value. It would save a lot of time for me.

And as an extra bonus, if this is possible, there is also a Liveweight slider, that updates the vertex group as I drag the slider, and I see the result right away. Pretty much like the Vertex weights in the Properties panel, but this affects all selected vertices.

Would this be possible, and where would I start? I have never coded anything in python, but I've been coding for a long time, mostly PHP and Javascript, so I think I can figure out the basics, if I get some pointers.

Also, is it possible to put this inside the Vertex Group section, or does it need to be in a separate panel?

Here's a rough screenshot of my idea as a separate panel, sorry for a weird number of buttons

Here's the code I've made so far. I got it working when I had another similar script loaded, but when I use only this, I only get the Panel, not the buttons. Is there a class I missed or something?

Now I'd be happy for some tips on finding the active vertex group and assigning the vertex values to the selected vertices.

I tried to implement the code, but I'm not sure if I should tab in the for loop, and make it iterate through all vertices.

bl_info = {
    "name": "Quickly set weights of Vertex Groups",
    "author": "nicmar",
    "version": (1, 0),
    "blender": (2, 78, 0),
    "location": "Properties Editor > Object data > Vertex Groups",
    "description": "Quickly set Vertex Groups with assigned weight and live edit",
    "warning": "",
    "wiki_url": "",
    "category": "Mesh"}

import bpy
import time

from bpy.types import Panel

class QuickWeightPanel(bpy.types.Panel):
    bl_label = "Quick Vertex Weights"
    bl_space_type = "PROPERTIES";
    bl_region_type = "WINDOW";
    bl_context = "data"
    #bl_category = "Test"
       
    def draw(self,context):
        layout = self.layout

        row = layout.row(align=True)
        row.alignment = 'EXPAND'
        row.operator("my.button", text="0").number=0
        row.operator("my.button", text="10").number=0.1
        row.operator("my.button", text="25").number=0.25
        row.operator("my.button", text="40").number=0.4
        row.operator("my.button", text="50").number=0.5
        row.operator("my.button", text="60").number=0.6
        row.operator("my.button", text="75").number=0.75
        row.operator("my.button", text="90").number=0.9
        row.operator("my.button", text="100").number=1


class MyOp(bpy.types.Operator): #The operator class derived from Operator
    bl_idname="my.button" #Same as in row.operator
    bl_label="my.button blabla" #Needed

    number=bpy.props.FloatProperty() #The property used in row.operator

    def execute(self, context): #Is trigered by buttons


        # Toggle into edit mode
        obj=bpy.context.active_object
        
        # Toggle into object mode (Wrong? I need to be in edit mode to set weights?)
        #prevMode = obj.mode
        #bpy.ops.object.mode_set(mode='OBJECT', toggle=False)

        # Get active vertex group index
        active_vertex_group_index = obj.vertex_groups.active_index

        # Should I use this?
        #g=obj.vertex_groups['group name']
        
        # Loop through and get all selected vertices i v (?)
        [v for v in obj.data.vertices if v.select] 
        # Get first?
        v = obj.data.vertices[0]
        # Get the data for the group accessed by the group index 
        vg=v.groups[active_vertex_group_index]
        # Set weight of active vertices in active weight group
        # vg.weight = 0.5
        # Print weight of current vertex
        print(vg.weight) 
        
        # Return to previous mode before operator 
        bpy.ops.object.mode_set(mode=prevMode, toggle=False)

        return {'FINISHED'}     


def register():
    bpy.utils.register_module(__name__)
    #bpy.types.Data.ignit_panel = bpy.props.PointerProperty(type=IgnitProperties)


def unregister():
    bpy.utils.unregister_module(__name__)
    #del bpy.types.Data.ignit_panel


if __name__ == "__main__":
    register()

Answer 1

If that can save you some time. See the commented part below:

bl_info = {
    "name": "Quickly set weights of Vertex Groups",
    "author": "nicmar",
    "version": (1, 0),
    "blender": (2, 78, 0),
    "location": "Properties Editor > Object data > Vertex Groups",
    "description": "Quickly set Vertex Groups with assigned weight and live edit",
    "warning": "",
    "wiki_url": "",
    "category": "Mesh"}

import bpy
import time
from bpy.types import Panel

class QuickWeightPanel(bpy.types.Panel):
    bl_label = "Quick Vertex Weights"
    bl_space_type = "PROPERTIES";
    bl_region_type = "WINDOW";
    bl_context = "data"
    #bl_category = "Tomte"

    def draw(self,context):

        layout = self.layout

        row = layout.row(align=True)
        row.alignment = 'EXPAND'
        
        row.operator("my.button", text="0").number=0
        row.operator("my.button", text="10").number=0.1
        row.operator("my.button", text="25").number=0.25
        row.operator("my.button", text="40").number=0.4
        row.operator("my.button", text="50").number=0.5
        row.operator("my.button", text="60").number=0.6
        row.operator("my.button", text="75").number=0.75
        row.operator("my.button", text="90").number=0.9
        row.operator("my.button", text="100").number=1

class MyOp(bpy.types.Operator): #The operator class derived from Operator
    bl_idname="my.button" #Same as in row.operator
    bl_label="my.button blabla" #Needed
    
    number=bpy.props.FloatProperty() #The property used in row.operator

    def execute(self, context): #Is trigered by buttons
        print("Test", self.number) #With the associated value
        return {'FINISHED'}

def register():
    bpy.utils.register_module(__name__)

def unregister():
    bpy.utils.unregister_module(__name__)

if __name__ == "__main__":
    register()

To go further on the addon:

• Active object and its type

obj=bpy.context.active_object

obj.type needs to be 'MESH'

• Object groups

obj.vertex_groups contains the groups.

Use obj.vertex_groups.new(...) to create one or remove(...) to remove

g=obj.vertex_groups['group name']

g.index used in vertices (see below)

obj.vertex_groups.active_index is the currently selected group in the property panel

• Object data

obj.data all object inner data

obj.data.vertices its vertices

[v for v in obj.data.vertices if v.select] selected vertices

v = obj.data.vertices[0]

v.groups contains the weights for each group v is involved in

vg=v.groups[groupIndex] the data for the group accessed by the group index

vg.weight is the weight

You'll probably need something like

prevMode = obj.mode

bpy.ops.object.mode_set(mode='OBJECT', toggle=False)

#... your code here

bpy.ops.object.mode_set(mode=prevMode, toggle=False)

To retrieve safely the selected vertices and come back to the mode selected before script execution.

Answer 2

In the newer versions of blender you need to use a colon symbol instead of equal symbol operator.

So the operator from the example above becomes:

class MyOp(bpy.types.Operator): 
bl_idname="my.button" 
bl_label="my.button blabla" 

number : bpy.props.FloatProperty() # Equal symbol is changed to colon

def execute(self, context): 
    print("Test", self.number) 
    return {'FINISHED'}

(This is an answer to the comment made by Gary, but I don't have enough reputation to comment)