As of January 2022 HelioPy will no longer be developed or supported. Most of HelioPy's functionality is now implemented elsewhere:
sunpy version 3.1 (released October 2021)
has support for reading CDF files. It also has functionality to search NASA's
CDAWeb via. sunpy.net.Fido
, which provides access to in-situ data from a
large range of in-situ heliospheric observatories.
The astrospice project re-implements all of this functionality, in a much more user and maintainer friendly codebase. It's currently actively developed, and accepting bug reports or feature requests.