Zappend

Enhancements

* A new configuration setting `append_step` can be used to validate
the step sizes between the labels of a coordinate variable associated with
the append dimension. Its value can be a number for numerical labels
or a time delta value of the form `8h` (8 hours) or `2D` (two days) for
date/time labels. The value can also be negative. (21)

* The configuration setting `append_step` can take the special values
`"+"` and `"-"` which are used to verify that the labels are monotonically
increasing and decreasing, respectively. (20)

* It is now possible to reference environment variables
in configuration files using the syntax `${ENV_VAR}`. (36)

* Added a demo Notebook `examples/zappend-demo.ipynb` and linked
it by a binder badge in README.md. (47)

Fixes

* When `slice_source` was given as class or function and passed
to the `zappend()` function either as configuration entry or as keyword
argument, a `ValidationError` was accidentally raised. (49)

* Fixed an issue where an absolute lock file path was computed if the target
Zarr path was relative in the local filesystem, and had no parent directory.
(45)

Enhancements

* Allow for passing custom slice sources via the configuration.
The new configuration setting `slice_source` is the name of a class
derived from `zappend.api.SliceSource` or a function that creates an instance
of `zappend.api.SliceSource`. If `slice_source` is given, slices passed to
the zappend function or CLI command will be interpreted as parameter(s)
passed to the constructor of the specified class or the factory function.
(27)

* It is now possible to configure runtime profiling of the `zappend`
processing using the new configuration setting `profiling`. (39)

* Added `--version` option to CLI. (42)

* Using `sizes` instead of `dims` attribute of `xarray.Dataset` in
implementation code. (25)

* Enhanced documentation including docstrings of several Python API objects.

Fixes

* Fixed a problem where the underlying i/o stream of a persistent slice dataset
was closed immediately after opening the dataset. (31)

* Now logging ignored encodings on level DEBUG instead of WARNING because they
occur very likely when processing NetCDF files.

Enhancements

* Introduced _slice factories_
- Allow passing slice object factories to the `zappend()` function.
Main use case is to return instances of a custom `zappend.api.SliceSource`
implemented by users. (13)

- The utility functions `to_slice_factories` and `to_slice_factory`
exported by `zappend.api` ease passing inputs specific for a custom
`SliceSource` or other callables that can produce a slice object. (22)

* Introduced new configuration flag `persist_mem_slices`.
If set, in-memory `xr.Dataset` instances will be first persisted to a
temporary Zarr, then reopened, and then appended to the target dataset. (11)

* Added initial documentation. (17)

* Improved readability of generated configuration documentation.

* Using `requirements-dev.txt` for development package dependencies.

Fixes

* Fixed problem when passing slices opened from NetCDF files. The error was
`TypeError: VariableEncoding.__init__() got an unexpected keyword argument 'chunksizes'`.
(14)

* Fixed problem where info about closing slice was logged twice. (9)

Metadata fixes in `setup.cfg`. No actual code changes.

*The initial release.*