Generates batched data in flat numpy arrays.

    Raises:
      ValueError: When too many generate calls are required.

def generate_flat_data(self):
    """Generates batched data in flat numpy arrays.

    Raises:
      ValueError: When too many generate calls are required.
    """
    # Construct the string statements.
    all_statements = []
    all_targets = []
    self.sequence_sizes_in = []
    self.sequence_sizes_out = []
    for _ in six.moves.range(self._batch_size):
      length, nest = self.curriculum_obj.fetch()
      seq_size_in = self._max_seq_length
      # Generate batch within max length.
      is_valid_sample = False
      tries_remaining = 10
      while not is_valid_sample:
        value, code = generate_code(length, nest, self._ops)
        tokens_in, seq_size_in = self.tokenize(
            code, self._max_seq_length, self._token_by_char)
        tokens_out, seq_size_out = self.tokenize(
            value, self._max_seq_length, self._token_by_char)
        is_valid_sample = self._max_seq_length >= seq_size_in
        if is_valid_sample:
          self.sequence_sizes_in.append(seq_size_in)
          self.sequence_sizes_out.append(seq_size_out)
        if tries_remaining == 0:
          raise ValueError("Could not generate a sample below the allowable "
                           "maximum, consider reducing either max_length or "
                           "max_nest.")
        else:
          tries_remaining -= 1
      all_statements += tokens_in
      all_targets += tokens_out
    # Store the flattened data.
    self.flat_data = np.array(all_statements, dtype=np.int64)
    self.num_tokens = self.flat_data.shape[0]
    self.flat_targets = np.array(all_targets, dtype=np.int64)
    self.num_tokens_target = self.flat_targets.shape[0]
    self.start_token = np.array(self.tokenize(
        [get_start_token()], 1)[0], dtype=np.int64)
    self.end_token = np.array(self.tokenize(
        [get_end_token()], 1)[0], dtype=np.int64)