default.nix

with import <nixpkgs> {};
runCommand "script" 
{ buildInputs = [ (python.withPackages (ps: with ps; [ numpy opencv3 ])) ]; } 
''
    mkdir -pv $out/bin/
    cp -vi ${./script.py} $out/bin/output
    patchShebangs $out/bin/
''

script.py

#!/usr/bin/env python2.7
import numpy as np
import cv2
import sys
import json
import os
import math
import warnings
import argparse
import string