code: def _shift_months_back(date, shift):
      assert date.day == 1, date
      for _day in range(shift):
          date = (date - timedelta(days=1)).replace(day=1)
      return date
  
imports: from datetime import datetime, date, time, timedelta
  from guild import _yacc
  from .None import trlex
label_desc: Use image node_id 33 for calling a global function with example usage: _shift_months_back(date, shift) and returns: date