code: def _env_vars_from_file(filename):
      
      def split_env(env):
          if '=' in env:
              return env.split('=', 1)
          else:
              return env, None
      env = {}
      for line in open(filename, 'r'):
          line = line.strip()
          if line and not line.startswith('#'):
              k, v = split_env(line)
              env[k] = v
      return env
docs: This code is copied from Docker Compose, so that we're exactly compatible
      with their `env_file` option