code: def asset_start(asset_info, asset):
      ret = asset_info.loc[asset]["start_date"]
      if ret.tz is None:
          ret = ret.tz_localize("UTC")
      assert ret.tzname() == "UTC", "Unexpected non-UTC timestamp"
      return ret
  
imports: from numpy import arange, array, eye, float64, full, iinfo, uint32
  from numpy.random import RandomState
  from pandas import DataFrame, Timestamp
  from six import iteritems
  from sqlite3 import connect
  from .base import PipelineLoader
  from .frame import DataFrameLoader
  from catalyst.data.us_equity_pricing import SQLiteAdjustmentReader, SQLiteAdjustmentWriter, US_EQUITY_PRICING_BCOLZ_COLUMNS
  from catalyst.utils.numpy_utils import bool_dtype, datetime64ns_dtype, float64_dtype, int64_dtype, object_dtype
label_desc: Use image node_id 2 for calling a global function with example usage: asset_start(asset_info, asset) and returns: ret