code: def calc_net(values):
      # Returns 0.0 if there are no values.
      return sum(values, np.float64())
  
imports: from __future__ import division
  import logbook
  import numpy
  from collections import namedtuple
  from math import isnan
  from six import iteritems, itervalues
  from catalyst.finance.performance.position import Position
  from catalyst.finance.transaction import Transaction
  from catalyst.utils.input_validation import expect_types
  import catalyst.protocol
  from catalyst.assets import Future, Asset
  from .position import positiondict
  from catalyst.constants import LOG_LEVEL
label_desc: Use image node_id 2 for calling a global function with example usage: calc_net(values) and returns: sum