pycsw is not a metadata editor.
pycsw is a fully compliant CSW server.
pycsw is flexible and headless; can be integrated into workflows without getting in the way, as well as seamless integration with Python environments.
pycsw is able to pull and store (“harvest”) layer information from other remote OGC services (WMS, WFS, WCS, WPS, WAF, CSW, SOS).
pycsw avoids any stylesheet conversions by storing metadata elements in a local database.
pycsw allows for remote updates to the local repository (“transactions”), through CSW-T.
pycsw allows for additional profiles/metadata formats to be plugged in.
pycsw includes a commandline utility to administer the metadata repository.
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Note
A detailed list of features and standards is maintained in the pycsw documentation here.