code: def where(cond, a, b, use_numexpr=True):
      
  
      if use_numexpr:
          return _where(cond, a, b)
      return _where_standard(cond, a, b)
docs: evaluate the where condition cond on a and b
  
          Parameters
          ----------
  
          cond : a boolean array
          a :    return if cond is True
          b :    return if cond is False
          use_numexpr : whether to try to use numexpr (default True)