class_docstr: Useful commands
  - run all tests: pytest examples/orderbook_data/example.py
  - run a single test:  pytest -s --pdb --disable-warnings examples/orderbook_data/example.py::TestClass::test_basic01
class_docstr_tok: ["Useful","commands","-","run","all","tests",":","pytest","examples\/orderbook_data\/example.py","-","run","a","single","test",":","pytest","-s","--","pdb","--","disable-warnings","examples\/orderbook_data\/example.py",":",":TestClass",":",":test_basic01"]
code: def expr7_3_init(funccode, code, time_interval):
      # NOTE: It depends on transaction frequency
      return f"Rolling(Eq($function_code,  {ord(funccode)}) & {code}($ask_order, $bid_order) , '{time_interval}s', 'sum') / Rolling($function_code, '{time_interval}s', 'count')"
  
imports: from arctic.arctic import Arctic
  import qlib
  from qlib.data import D
  import unittest
label_desc: Use image node_id 17 for calling the TestClass obj's underlying member method code with example usage: obj.expr7_3_init(funccode, code, time_interval) and returns: str, ord, str, code, str, time_interval, str, time_interval, str