Blender Sushi Script to select some meshes within specific distance to an Empty in 3D scene. User can adjust the Distance value.

jgbpy_selectMeshBasedOnDistance.py

import bpy

def selectMeshBasedOnDistance(distance, empty):
    """
    A simple script to calculate the distance of all
    mesh in the scene relative to the selected camera
    """
    
    # Firstly, deselect all objects in the scene
    bpy.ops.object.select_all(action='DESELECT')  
        
    # Get all objects in the scene of type 'MESH'
    meshes = []
    for item in bpy.data.objects:  
        if item.type == 'MESH':  
            meshes.append(item)
    
    # Check if empty argument given is a type of empty
    if empty.type != 'EMPTY':
        print("Please specify an empty!")

    # Create and clear an array to store mesh within the specified distance
    meshToSelect = []
    del(meshToSelect[:])
    print(meshToSelect)
    
    # Get the camera positions in world space
    #emptyXform = empty.matrix_world * empty.location
    emptyXform = empty.location

    # Get the mesh xform and distance from camera
    for mesh in meshes:
        #meshXform = mesh.matrix_world * mesh.location
        meshXform = mesh.location
        meshDistanceFromEmpty=(meshXform-emptyXform).length
        print(mesh, meshDistanceFromEmpty)
        if meshDistanceFromEmpty < distance:
            meshToAdd = []
            meshToAdd = mesh
            meshToSelect.append(meshToAdd)
    print(meshToSelect)
        
    # adding if for error checking, Python does not like selecting empty list
    if(len(meshToSelect))>0:
        for item in meshToSelect:
            item.select=True

# My Test 1:  
# selectMeshBasedOnDistance(20, bpy.context.selected_objects[0])

# My Test 2:  
selectMeshBasedOnDistance(5, bpy.data.objects['Empty'])