ppfive 0.1.1

PP/Fields reader with pyfive-style high-level API

ppfive

A PP and Fields file reader that mimics relevant parts of the pyfive high-level API, with support for lazy metadata loading and parallel data loading when necessary.

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 (ppfive vs pyfive)

ppfive 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

• ppfive.File is registered as a pyfive.File virtual type (when pyfive is installed).
• ppfive.Variable is registered as a pyfive.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, ppfive 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, external, is_virtual.
• 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.
• ppfive-specific extension API:
  • File.set_parallelism(thread_count=..., cat_range_allowed=...) is provided by ppfive and is not part of pyfive.

Practical expectation

If your code treats ppfive.File and ppfive.Variable as pyfive-like read objects, 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)