How can i get the weight for all vertices in a vertex group? I have created this function to get the weights from a group:

def get_weights(ob, vgroup):
    weights = []
    for index, vert in enumerate(ob.data.vertices):
        for group in vert.groups:
            if group.group == vgroup.index:
                weights.append([index, group.weight])
    return weights


Is there any better more efficient way to do this?
For The RNA mesh API, your example is quite good, one minor change you can make is to break once the group index is found.

Instead of making a large list, you could use a generator function, this can save memory for the cases you can iterate over the elements, and be converted to a list or tuple if you need, it has the same worst-case time, but in practice will often save some looping.

import bpy
obj = bpy.context.object

def get_weights(ob, vgroup):
    group_index = vgroup.index
    for i, v in enumerate(ob.data.vertices):
        for g in v.groups:
            if g.group == group_index:
                yield (i, g.weight)
                break

import bpy
obj = bpy.context.object
vgroup = obj.vertex_groups[0]

# iterate over index, weights
for i, w in get_weights(obj, vgroup):
    print(i, w)

# if you need as a list...
weights = list(get_weights(obj, vgroup))
print(weights)


Note, in some similar cases to this, you can use list-comprehension, however having to check the vertex is in the group causes the checks within the list-comprehension to become quite convoluted, so best avoid in this case.