class_docstr: This plan is used for storing information required for sample
  operations.
  
  Arguments:
      sample_freq: ConstantValueExpression
          A ConstantValueExpression which is the count of the
          gap between frames sampled.
code: def __str__(self):
      return "SamplePlan(sample_freq={})".format(self._sample_freq)
  
file_path: evadb/evadb/plan_nodes/sample_plan.py
imports: from evadb.expression.constant_value_expression import ConstantValueExpression
  from evadb.plan_nodes.abstract_plan import AbstractPlan
  from evadb.plan_nodes.types import PlanOprType
label_desc: Use image node_id 3 for calling the SamplePlan obj's underlying member method code with example usage: obj.__str__() and returns: str