Adopt PEP8 in MONAI/examples/notebooks/

[Warvito]

Is your feature request related to a problem? Please describe.
Some notebooks are not following the PEP8 style guide.

Describe the solution you'd like
Please, consider following the PEP8 style guide in the notebooks from MONAI/examples/notebooks/.
For example, in examples/notebooks/mednist_tutorial.ipynb, cell 4 has variables named using the CamelCase style instead snake_case (https://www.python.org/dev/peps/pep-0008/#id45), for example:

dataDir = './MedNIST/'
classNames = os.listdir(dataDir)
numClass = len(classNames)

Later, in the same notebook, the snake_case is adopted.

train_ds = MedNISTDataset(trainX, trainY, train_transforms)
train_loader = DataLoader(train_ds, batch_size=300, shuffle=True, num_workers=10)

val_ds = MedNISTDataset(valX, valY, val_transforms)
val_loader = DataLoader(val_ds, batch_size=300, num_workers=10)

[Warvito]

Please, also consider make consistent:

• the use of single and double quotes;
• the use of %-string formatting vs .format()-string formatting (I recommend the latter as suggested in the python docs https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting ).

[tvercaut]

This could be relevant to run flake8 on the notebooks:
https://stackoverflow.com/questions/26126853/verifying-pep8-in-ipython-notebook-code

[Nic-Ma]

Hi @Warvito ,

Thanks very much for your bug report!
I already submitted PR Project-MONAI/MONAI#301 to fix the issues in all the examples and notebooks, mainly include:

1. CamelCase style.
2. some missing blank space.
3. unify to use single quote.
4. unify to use string.format().
5. some missing dependencies in notebook.

Welcome to review the PR if you have interest.
Thanks.

[wyli]

this is still an issue and I think we need a more 'systematic' solution... Project-MONAI/MONAI#340 Project-MONAI/MONAI#346 only address those .py files

[wyli]

addressed by #107