vfdev-5: @miguelvr can you also add a test for the argument ?
miguelvr: Sure thing 
miguelvr: @vfdev-5 I'm trying to do something similar to what I've done with the other unit tests.

However, I'm getting weird behaviours.

The snippet for the code is like this:
```python
def test_pbar_no_metric_names(capsys):

    n_epochs = 2
    loader = [1, 2]
    engine = Engine(update_fn)

    pbar = ProgressBar()
    pbar.attach(engine)

    engine.run(loader, max_epochs=n_epochs)

    captured = capsys.readouterr()
    stderr = captured.err.split('\r')
    err = list(map(lambda x: x.strip(), stderr))
    err = list(filter(None, err))
    actual = err[-1]
    expected = u'Epoch 2: [1/2]  50%|█████      [00:00<00:00]'
    assert actual == expected
```

The comparison with the stderr string is behaving in a weird way and I'm obtaining a bunch of hexadecimal characters. However, if I debug and do everything manually the assertion checks out...
miguelvr: LGTM!
diff --git a/ignite/contrib/handlers/tqdm_logger.py b/ignite/contrib/handlers/tqdm_logger.py
index 196f57f7..61a742ad 100644
--- a/ignite/contrib/handlers/tqdm_logger.py
+++ b/ignite/contrib/handlers/tqdm_logger.py
@@ -47,6 +47,7 @@ class ProgressBar:
 
         if metric_names is not None:
             if not all(metric in engine.state.metrics for metric in metric_names):
+                self._close(engine)
                 raise KeyError("metrics not found in engine.state.metrics")
 
             metrics = {name: '{:.2e}'.format(engine.state.metrics[name]) for name in metric_names}
@@ -72,7 +73,7 @@ class ProgressBar:
             engine (Engine): engine object
             metric_names (list): (Optional) list of the metrics names to log as the bar progresses
         """
-        if not isinstance(metric_names, list):
+        if metric_names is not None and not isinstance(metric_names, list):
             raise TypeError("metric_names should be a list, got {} instead".format(type(metric_names)))
 
         engine.add_event_handler(Events.EPOCH_COMPLETED, self._close)

tqm_logger: metric_names is currently not optional 
Hi,

https://github.com/pytorch/ignite/blob/master/ignite/contrib/handlers/tqdm_logger.py#L75
This line should be modified to make `metric_names` optional. Here is a suggestion:
```
if metric_names is not None and not isinstance(metric_names, list):
    raise TypeError("metric_names should be a list, got {} instead".format(type(metric_names)))
```

Thanks
diff --git a/tests/ignite/contrib/handlers/test_pbar.py b/tests/ignite/contrib/handlers/test_pbar.py
index aeecbb51..1fd3a68b 100644
--- a/tests/ignite/contrib/handlers/test_pbar.py
+++ b/tests/ignite/contrib/handlers/test_pbar.py
@@ -66,3 +66,23 @@ def test_pbar_with_metric():
 
     with pytest.raises(KeyError):
         trainer.run(data=data, max_epochs=1)
+
+
+def test_pbar_no_metric_names(capsys):
+
+    n_epochs = 2
+    loader = [1, 2]
+    engine = Engine(update_fn)
+
+    pbar = ProgressBar()
+    pbar.attach(engine)
+
+    engine.run(loader, max_epochs=n_epochs)
+
+    captured = capsys.readouterr()
+    err = captured.err.split('\r')
+    err = list(map(lambda x: x.strip(), err))
+    err = list(filter(None, err))
+    actual = err[-1]
+    expected = u'Epoch 2: [1/2]  50%|█████      [00:00<00:00]'
+    assert actual == expected

pip install -e .
parse_log_pytest
pytest
numpy mock pytest codecov pytest-cov tqdm scikit-learn visdom torchvision tensorboardX gym
apt-get update apt-get install -y gcc
3.6
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
attrs @ file:///opt/conda/conda-bld/attrs_1642510447205/work
certifi==2021.5.30
charset-normalizer==2.0.12
cloudpickle==2.2.1
codecov==2.1.13
coverage==6.2
dataclasses==0.8
decorator==4.4.2
gym==0.26.2
gym-notices==0.0.8
idna==3.10
importlib-metadata @ file:///tmp/build/80754af9/importlib-metadata_1631916693255/work
importlib-resources==5.4.0
iniconfig @ file:///home/linux1/recipes/ci/iniconfig_1610983019677/work
joblib==1.1.1
jsonpatch==1.32
jsonpointer==2.3
mock==5.2.0
more-itertools @ file:///tmp/build/80754af9/more-itertools_1637733554872/work
networkx==2.5.1
numpy==1.19.5
packaging @ file:///tmp/build/80754af9/packaging_1637314298585/work
Pillow==8.4.0
pluggy @ file:///tmp/build/80754af9/pluggy_1615976315926/work
protobuf==4.21.0
py @ file:///opt/conda/conda-bld/py_1644396412707/work
pyparsing @ file:///tmp/build/80754af9/pyparsing_1635766073266/work
pytest==6.2.4
pytest-cov==4.0.0
-e git+https://github.com/pytorch/ignite.git@83fe17dd513a4f0ed7fe1cfea6ea00541557465b#egg=pytorch_ignite
requests==2.27.1
scikit-learn==0.24.2
scipy==1.5.4
six==1.17.0
tensorboardX==2.6.2.2
threadpoolctl==3.1.0
toml @ file:///tmp/build/80754af9/toml_1616166611790/work
tomli==1.2.3
torch==1.10.1
torchvision==0.11.2
tornado==6.1
tqdm==4.64.1
typing_extensions @ file:///opt/conda/conda-bld/typing_extensions_1647553014482/work
urllib3==1.26.20
visdom==0.2.4
websocket-client==1.3.1
zipp @ file:///tmp/build/80754af9/zipp_1633618647012/work

name: ignite
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - attrs=21.4.0=pyhd3eb1b0_0
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - importlib-metadata=4.8.1=py36h06a4308_0
  - importlib_metadata=4.8.1=hd3eb1b0_0
  - iniconfig=1.1.1=pyhd3eb1b0_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - more-itertools=8.12.0=pyhd3eb1b0_0
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - packaging=21.3=pyhd3eb1b0_0
  - pip=21.2.2=py36h06a4308_0
  - pluggy=0.13.1=py36h06a4308_0
  - py=1.11.0=pyhd3eb1b0_0
  - pyparsing=3.0.4=pyhd3eb1b0_0
  - pytest=6.2.4=py36h06a4308_2
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - toml=0.10.2=pyhd3eb1b0_0
  - typing_extensions=4.1.1=pyh06a4308_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zipp=3.6.0=pyhd3eb1b0_0
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - charset-normalizer==2.0.12
      - cloudpickle==2.2.1
      - codecov==2.1.13
      - coverage==6.2
      - dataclasses==0.8
      - decorator==4.4.2
      - gym==0.26.2
      - gym-notices==0.0.8
      - idna==3.10
      - importlib-resources==5.4.0
      - joblib==1.1.1
      - jsonpatch==1.32
      - jsonpointer==2.3
      - mock==5.2.0
      - networkx==2.5.1
      - numpy==1.19.5
      - pillow==8.4.0
      - protobuf==4.21.0
      - pytest-cov==4.0.0
      - requests==2.27.1
      - scikit-learn==0.24.2
      - scipy==1.5.4
      - six==1.17.0
      - tensorboardx==2.6.2.2
      - threadpoolctl==3.1.0
      - tomli==1.2.3
      - torch==1.10.1
      - torchvision==0.11.2
      - tornado==6.1
      - tqdm==4.64.1
      - urllib3==1.26.20
      - visdom==0.2.4
      - websocket-client==1.3.1
prefix: /opt/conda/envs/ignite

tests/ignite/contrib/handlers/test_pbar.py::test_pbar_no_metric_names
tests/ignite/contrib/handlers/test_pbar.py::test_pbar tests/ignite/contrib/handlers/test_pbar.py::test_attach_fail_with_string tests/ignite/contrib/handlers/test_pbar.py::test_pbar_with_metric
ignite/contrib/handlers/tqdm_logger.py
ignite/contrib/handlers/tqdm_logger.py