code: def __len__(self):
      return len(self.array)
  
imports: import numpy
  from ..base import BaseEstimator, ClassifierMixin
  from .testing import assert_true
  from .validation import _num_samples, check_array
label_desc: Use image node_id 2 for calling the MockDataFrame obj's underlying member method code with example usage: obj.__len__() and returns: len