Can't see any indication in the 3D view , when changing mesh properties from python console Im using blender 2.75 in windows , i try to change the default cube model simple property data.edge[0].bevel_weight to 1.0 
but i don't see any bevel change in the cube model in the 3d View 
in the python console i do :

&gt;&gt;&gt; cube  = bpy.context.active_object
&gt;&gt;&gt; cube.data.edges[0]
bpy.data.meshes['Cube'].edges[0]
&gt;&gt;&gt; cube.data.edges[0].bevel_weight
0.0
&gt;&gt;&gt; cube.data.edges[1].bevel_weight = 1.0
&gt;&gt;&gt; cube.data.edges[1].bevel_weight
1.0


looks like in the script it is working but why i dont see any thing in the 3DView?
Make sure you aren't in edit mode. If this is part of a larger script (your example looks like Python Console code), the standard practice is to go into object mode, perform your actions, then enter edit mode again, ie.

import bpy

cube = bpy.context.active_object

# store editor state
is_editmode = (cube.mode == 'EDIT')
if is_editmode:
    bpy.ops.object.mode_set(mode='OBJECT', toggle=False)

# make your changes
cube.data.edges[0].bevel_weight = 1

# restore editor state
if is_editmode:
    bpy.ops.object.mode_set(mode='EDIT', toggle=False)