umfive

umfive is a Python open source library for representing UK Met Office PP and UM fields file datasets with CF-netCDF-like structures that follow the API of pyfive, an HDF5 reader.

Read the umfive documentation

This is NOT an alternative to pyfive, it is a package which makes pp and fields files look like and taste ("quack like") chunked HDF5 files written by a NetCDF library.

API Contract (umfive vs pyfive)

umfive is designed to be pyfive-compatible as far as likely users of pyfive would need such compatability. That is, it produces a chunk index (for kerchunk) if you really want that, and it supports all the information needed by CF/CFDM workflows to make pp-data as CF-compliant as possible.

For the canonical pyfive interface, see the pyfive docs:

• https://pyfive.readthedocs.io/

What maps directly to pyfive

• umfive.File is registered as a umfive.File virtual type (when umfive is installed).
• umfive.Variable is registered as a umfive.Dataset virtual type.
• File/root-level members expected by pyfive-style callers are present:
  • attrs, groups, variables, dimensions, name, path, parent
• Mapping-style access works:
  • f["var"], iteration over variables, items(), len(f)
• Dataset-like variable members needed by downstream consumers are present:
  • shape, dtype, ndim, size, attrs, chunks/chunk_shape, file, parent
  • slicing/indexing via __getitem__ (for example f["var"][:])
  • read_direct, astype(...), iter_chunks(...)

Like pyfive, umfive is read-only:

- `File(..., mode="r")` is supported; write/update modes are not.

Important differences from pyfive

• No nested groups in PP/Fields model:
  • f["group/var"] is not supported.
  • groups exists for compatibility but is empty for current PP/Fields inputs.
• get_lazy_view(...) fallback behavior:
  • pyfive-style API entry exists, but returns the normal variable view with an info log.
• Some Dataset properties are intentionally placeholders (None) because they are not meaningful for PP/Fields records:
  • compression, compression_opts, shuffle, fletcher32, maxshape, fillvalue, dims, scaleoffset.
• Compatibility metadata is synthesized for CF/cfdm bridging:
  • dimension-scale datasets and DIMENSION_LIST are created where needed.
  • rotated-grid helper variables (for example latitude, longitude, rotated_latitude_longitude) may be exposed when implied by UM headers.
• umfive-specific extension API:
  • File.set_parallelism(thread_count=..., cat_range_allowed=...) is provided by umfive and is not part of pyfive.

Practical expectation

If your code treats umfive.File as a pyfive-like read object, common analysis workflows should work, including chunk-level access (PP records are treated as chunks).

Authorship

Key authors of this package are:

• David Hassell (@davidhassell)
• Alan Iwi (@alaniwi)
• Bryan Lawrence (@bnlawrence)