code: def test_string_prefix(self, strings):
      length = 3
      # although we are utf-8 encoding below to avoid python exceptions,
      # StringPrefix op deals with byte-length prefixes, which may produce
      # an invalid utf-8 string. The goal here is just to avoid python
      # complaining about the unicode -> str conversion.
      strings = np.array(
          [a.encode("utf-8") for a in strings], dtype=object
      )
  
      def string_prefix_ref(strings):
          return (
              np.array([a[:length] for a in strings], dtype=object),
          )
  
      op = core.CreateOperator(
          "StringPrefix", ["strings"], ["stripped"], length=length
      )
      self.assertReferenceChecks(
          hu.cpu_do, op, [strings], string_prefix_ref
      )
  
file_path: pytorch/caffe2/python/operator_test/string_ops_test.py
imports: from caffe2.python import core
  from hypothesis import given, settings
  import caffe2.python.hypothesis_test_util
  import caffe2.python.serialized_test.serialized_test_util
  import hypothesis.strategies
  import numpy
label_desc: Use image node_id 1 for calling the TestStringOps obj's underlying member method code with example usage: obj.test_string_prefix(strings) and returns: np