def top_down_once(rule, fns=basic_fns):
    return do_one(rule, lambda expr: sall(top_down(rule, fns), fns)(expr))
If this is a shapefile, return the names of the fields in the DBF and their datattypes.  If this is a data
dataset/ETHPy150Open sympy/sympy/sympy/strategies/traverse.py/top_down_once--crossover with--dataset/ETHPy150Open hydroshare/hydroshare2/ga_resources/drivers/__init__.py/Driver.get_data_fields