This package provides a python wrapper around the IBM Informix C-ISAM library or alternatively the provided vbisam open source library that provides a drop-in replacement of the C-ISAM library.
The primary reason for this package was to permit a virtual table implementation to be written for the APSW SQLite wrapper package, without having to resort to writing an extension module.
Although the original C-ISAM is owned and copyrighted by IBM, who now owns the product, originally provided by Informix, both the 32-bit and 64-bit variants of the libaries for Linux are in the git repository.
Also as part of the repository is a slightly modified version of VBISAM (v2.1.1) at the time, which can be built using the meson build system, a copy of the library is included built as a 64-bit library.
In order to generate the necessary lowlevel interface extensions, use the following command:
$ python utils/bldlibisam.py
this will generate and copy all the necessary files that are required by the backend support.
The default setting of the backend is to use CFFI and the VBISAM library. To change this modify the conf.py or set the environment variable 'PYISAM_BACKEND'.
The variable should have the format 'BACKEND.VARIANT' where BACKEND is one of 'ctypes' or 'cffi', VARIANT is one of 'ifisam', or 'vbisam'.
A number of tests are provided which makes use of the sample data found in the 'data' directory, this are also the tables defined in the 'pyisam.tabdefnsr.stxtables' module. To run all the tests, run the following command:
$ python -m tests
To run a particular test, run the following command:
$ python -m tests -tNUM
To get help on the tests, run the following command:
$ python -m tests -h
As C-ISAM and VBISAM do not natively store the layout of a record, there is a need to provide the definition manually using a similar way that the sample tables are defined in the 'pyisam/tabdefns' subdirectory. As an alternative, the record can be constructed at runtime using the DynamicTableDefn defined in 'pyisam.tabdefns.dynamic'.
The 'pyisam.tabdefns.fldfile' module provides an conversion from the '.fld' file as used by the legacy SuperNova program, now owned by MicroFocus, and generates an instance of the 'DynamicTableDefn' which fields named as 'fldNNN' where NNN is an incrementing number starting from 1, as there are no field names stored within the '.fld' file. Also, there is no index information stored either, this is picked up by 'ISAMtable' when the first 'read' is invoked, in this case the indexes are named 'INDEXnnn' where nnn is likewis an incrementing number from 1.
The 'pyisam.tabdefns.stxtables' module provides, currently, a small number of table defintions that have been created manually, which provides both field and index information including names that correspond to tables used the legacy Strategix/OneOffice product, originally produced by TIS Software Ltd, now owned by Kerridge Commerical Systems. An alternative module will provide the '.dsc' file which provides the field and indexes which can be used to generate an instance of 'DynamicTableDefn' in a similar way to the 'fldfile' module does.
Currently there is no installation method to install the package into place, as this is still a work in progress.