with ruamel.yaml==0.14.12 or older, the 'vnfsdk csar-validate' reports the following warnings:

home/lulianhao/onap/vnfsdk/pkgtools/vnfsdk_pkgtools/packager/csar.py:264: UnsafeLoaderWarning:
The default 'Loader' for 'load(stream)' without further arguments can be unsafe.
Use 'load(stream, Loader=ruamel.yaml.Loader)' explicitly if that is OK.
Alternatively include the following in your code:

import warnings
warnings.simplefilter('ignore', ruamel.yaml.error.UnsafeLoaderWarning)

In most other cases you should consider using 'safe_load(stream)'
self.metadata.update(yaml.load(f))