FIX: a temporary workaround for pip-19.0.1 issues
MODIFY
repo2docker/buildpacks/python/__init__.py
repo2docker/buildpacks/python/__init__.py
@@ -63,6 +63,7 @@ class PythonBuildPack(CondaBuildPack):
if os.path.exists(requirements_file):
assemble_scripts.append((
'${NB_USER}',
+ 'pip install "pip<19" && ' + \
'{} install --no-cache-dir -r "{}"'.format(pip, requirements_file)
))

FIX: a temporary workaround for pip-19.0.1 issues