• Attribute data with a single value is now returned as a Python scalar instead of a numpy array.

  • Added missing changelog entries for 1.1.1 and 1.1.2.


  • Fixed a minor bug when writing CDF files.


  • Added terminate_on_warning and auto_fix_depends options to ~cdflib.xarray.xarray_to_cdf.xarray_to_cdf. See the docstring for more info.


  • If the deflate library is installed it is now used to decompress data, which can lead to around 2x speedups over the native gzip Python library.

  • Fixed reading attributes with multiple entries when using cdflib.cdfread.CDF.globalattsget.



  • Fixed issue where multi-dimensional variables were dropped when converting to xarray.

  • Replaced all print and warning statements with a logger, cdflib.logging.logger.


  • The variable parameter to cdflib.cdfread.CDF.varattsget is no longer optional. Not specifying it raised an error anyway in previous versions of cdflib.

  • Fixed an error loading CDF files without a pad value set.


To make the xarray functionality easier to discover and import, a new cdflib.xarray namespace has been added. This means the recommended way to import the xarray functionality is now from cdflib.xarray import cdf_to_xarray, xarray_to_cdf


To keep astropy and xarray as optional dependencies, cdfastropy, cdf_to_xarray, and xarray_to_cdf are no longer available under cdflib. Instead import them from cdflib.xarray_to_cdf.xarray_to_cdf, cdflib.cdf_to_xarray.cdf_to_xarray, or cdflib.epochs_astropy.CDFAstropy.


Version 1.0.0 is a new major version for cdflib, and contains a number of breaking changes. These have been made to improve consistency across the package, and make it easier to maintain and build on the package going forward in the future.

Although we have tried our best to not introduce new bugs and list all changes below, some things may have slipped through the cracks. If you have any issues, please do not hesitate to open them at

Python support

cdflib is now only tested on Python 3.8, 3.9, 3.10, and 3.11. It may work for older versions of Python, but this is not guarenteed. If you need to use cdflib on an older version of Python, please open an issue to discuss whether the cdflib maintainers can support this.

Returning arrays

All to_np keyword arguments have been removed throughout the library, and the code now behaves as if to_np=True throughout. This change has been made to reduce code omplexity and make maintaining the code easier. If you need outputs as lists, call .tolist() on the output array.

to_np=True was the deafult in cdfread, so if you weren’t specifying it behaviour will not change there. to_np=False was the default in epochs, so if you weren’t specifying it there beahviour will change.

Changes to CDF method returns

Most of the methods that return data from the CDF reader class have had their return types changed from dictionaries to dataclasses. This allows the return type to be more clearly documented (see Dataclasses), for internal checks to be made to make sure data types are consistent, and a nicer representation when the return values are printed.

Where previously an item would have been accessed as dict["value"], items in the dataclasses can be accessed using dataclass.value.

The methods that have been updated are:

Other breaking changes

  • The CDF factory class (cdflib.CDF) has been removed, and cdflib.CDF is now the reader class. This change has been made to prevent potential confusion when the user makes a mistake in specifying the file to open, and cdflib would silently create a writer class instead. If you want to create a CDF writer class, explicitly import cdflib.cdfwrite.CDF instead.

  • cdflib.cdfread.CDF.varget no longer takes an inq argument. Instead use the new method cdflib.cdfread.CDF.vdr_info to get the VDR info.

  • getVersion() methods have been removed throughout the package. Instead the CDF version can be read from class attributes.

  • Removed cdflib.cdfepochs.CDFepoch.getLeapSecondLastUpdated. Directly inspect CDFepoch.LTS instead to get the last date at which a leapsecond was added.

  • The expand keyword argument to cdflib.cdfread.CDF.varget has been removed. Use CDF.varinq to get variable information instead.

  • The expand keyword argument to CDF.globalattsget and CDF.varattsget has been removed. Use cdflib.cdfread.CDF.attinq to get attribute information instead.

  • Removed CDF.print_attrs

  • The version, release, and increement attributes of CDF have been removed.

  • Removed the record_range_only argument to cdflib.cdfread.CDF.varget.

  • Removed CDF.epochrange. Use cdflib.cdfread.CDF.varinq instead to get the data ranges.

New features

  • Type hints have been added across the majority of the package.


  • "Majority" is now correctly read from the CDF spec if present.