class_docstr: Tacotron2 module for end-to-end text-to-speech (E2E-TTS).
  
  This is a module of Spectrogram prediction network in Tacotron2 described
  in `Natural TTS Synthesis
  by Conditioning WaveNet on Mel Spectrogram Predictions`_,
  which converts the sequence of characters
  into the sequence of Mel-filterbanks.
  
  .. _`Natural TTS Synthesis by Conditioning WaveNet on Mel Spectrogram Predictions`:
     https://arxiv.org/abs/1712.05884
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docstr: Return base key names to plot during training.
  
  keys should match what `chainer.reporter` reports.
  If you add the key `loss`, the reporter will report `main/loss`
  and `validation/main/loss` values.
  also `loss.png` will be created as a figure visulizing `main/loss`
  and `validation/main/loss` values.
  
  Returns:
      list: List of strings which are base keys to plot during training.
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code: def base_plot_keys(self):
      """Return base key names to plot during training.
  
      keys should match what `chainer.reporter` reports.
      If you add the key `loss`, the reporter will report `main/loss`
      and `validation/main/loss` values.
      also `loss.png` will be created as a figure visulizing `main/loss`
      and `validation/main/loss` values.
  
      Returns:
          list: List of strings which are base keys to plot during training.
  
      """
      plot_keys = ["loss", "l1_loss", "mse_loss", "bce_loss"]
      if self.use_guided_attn_loss:
          plot_keys += ["attn_loss"]
      if self.use_cbhg:
          plot_keys += ["cbhg_l1_loss", "cbhg_mse_loss"]
      return plot_keys
  
imports: import logging
  import numpy
  import torch
  import torch.nn.functional
  from espnet.nets.pytorch_backend.nets_utils import make_non_pad_mask
  from espnet.nets.pytorch_backend.rnn.attentions import AttForward, AttForwardTA, AttLoc
  from espnet.nets.pytorch_backend.tacotron2.cbhg import CBHG, CBHGLoss
  from espnet.nets.pytorch_backend.tacotron2.decoder import Decoder
  from espnet.nets.pytorch_backend.tacotron2.encoder import Encoder
  from espnet.nets.tts_interface import TTSInterface
  from espnet.utils.cli_utils import strtobool
  from espnet.utils.fill_missing_args import fill_missing_args
label_desc: Use image node_id 6 for calling the Tacotron2 obj's underlying member method code with example usage: obj.base_plot_keys() and returns: plot_keys