code: def check_length(self, col=None):
      if type(self.obj) == ps.DataFrame or col is not None:
          return len(self.obj[col])
      else:
          try:
              return len(self.obj)
          except Exception as e:
              raise ValueError(str(e))
  
imports: import contextlib
  import numpy
  import pandas
  from pyspark import pandas
  from pyspark.testing.pandasutils import assert_produces_warning, ComparisonTestBase
  from pyspark.pandas.extensions import register_dataframe_accessor, register_series_accessor, register_index_accessor
label_desc: Use image node_id 4 for calling the CustomAccessor obj's underlying member method code with example usage: obj.check_length(col) and returns: len, len