Configuration to get Jupyter Lab's editor to trim whitespace at the end of each line when it saves a file.

jupyter-lab-config.py

# 1. Run: jupyter lab --generate-config
# 2. Edit $PATH/.jupyter/jupyter-lab-config.py, add the following at the end.
#
# In Jupyterhub, one needs to restart their "server" to get such config changes to take.

def strip_ws(t):
    return '\n'.join([i.rstrip() for i in t.split('\n')])


def scrub_output_pre_save(model=None, **kwargs):
    # """strip trailing space before saving"""
    if model['type'] == 'notebook':
        if model['content']['nbformat'] != 4:
            import sys
            print("skipping WS stripping since `nbformat` != 4", file=sys.stderr)
            return
        for cell in model['content']['cells']:
            if cell['cell_type'] == 'code':
                cell['source'] = strip_ws(cell['source'])
    elif model['type'] == 'file':
        if model['format'] == 'text':
            model['content'] = strip_ws(model['content'])


c.ContentsManager.pre_save_hook = scrub_output_pre_save