class_docstr: The Tqdm callback outputs the progress and metrics for training and validation loops to the console using TQDM.
  The given key is used to label validation output.
  
  Example: ::
  
      >>> import torch.nn
      >>> from torchbearer import Trial
      >>> from torchbearer.callbacks import Tqdm
  
      # Example Trial which forgoes the usual printer for a customised tqdm printer.
      >>> printer = Tqdm(precision=8)
      # Note that outputs are written to stderr, not stdout as shown in this example
      >>> trial = Trial(None, callbacks=[printer], verbose=0).for_steps(1).run(1)
      0/1(t): 100%|...| 1/1 [00:00<00:00, 29.40it/s]
  
  Args:
      tqdm_module: The tqdm module to use. If none, defaults to tqdm or tqdm_notebook if in notebook
      validation_label_letter (str): The letter to use for validation outputs.
      precision (int): Precision of the number format in decimal places
      on_epoch (bool): If True, output a single progress bar which tracks epochs
      tqdm_args: Any extra keyword args provided here will be passed through to the tqdm module constructor.
          See `github.com/tqdm/tqdm#parameters <https://github.com/tqdm/tqdm#parameters>`_ for more details.
  
  State Requirements:
      - :attr:`torchbearer.state.EPOCH`: The current epoch number
      - :attr:`torchbearer.state.MAX_EPOCHS`: The total number of epochs for this run
      - :attr:`torchbearer.state.STEPS`: The total number of steps / batches / iterations for this epoch
      - :attr:`torchbearer.state.METRICS`: The metrics dict to print
      - :attr:`torchbearer.state.HISTORY`: The history of the :class:`.Trial` object
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code: def _update(self, state):
      self._loader.update(1)
      self._loader.set_postfix_str(
          _format_metrics(state[torchbearer.METRICS], self.rounder)
      )
  
imports: from __future__ import print_function
  from collections import OrderedDict
  from functools import partial
  from tqdm import tqdm
  import torchbearer
  from torchbearer.callbacks import Callback
label_desc: Use image node_id 3 for calling the Tqdm obj's underlying member method code with example usage: obj._update(state) without return types