bai2 0.15.0

BAI2 Parser

Python module for parsing and writing BAI2 files.

The library is not production ready at the moment as we don’t have enough data to test against, please help us improve it.

Requirements

Only tested on Python 3.10+, but should work on 3.7+.

Installation

pip install bai2

Usage

To use bai2 in a project

from bai2 import bai2

# parse from a file
with open(<file-path>) as f:
    bai2_file = bai2.parse_from_file(f)

# parse from a string
bai2_file = bai2.parse_from_string(<bai2_as_string>)

# parse from lines
bai2_file = bai2.parse_from_lines(<bai2_as_lines>)

The parse_from_* methods return a bai2.models.Bai2File object which can be used to inspect the parsed data.

To write a BAI2 file:

from bai2 import bai2
from bai2 import models

bai2_file = models.Bai2File()
bai2_file.header.sender_id = 'EGBANK'

bai2_file.children.append(models.Group())

transactions = [models.TransactionDetail(amount=100)]
bai2_file.children[0].children.append(models.Account(children=transactions))

# write to string
output = bai2.write(bai2_file)

Models

Models structure:

Bai2File
    Bai2FileHeader
    Group
        GroupHeader
        Account
            AccountIdentifier
            TransactionDetail
            AccountTrailer
        GroupTrailer
    Bai2FileTrailer

Section models define a header, a trailer and a list of children whilst single models define properties matching the bai2 fields.

Each Model has a rows property with the original rows from the BAI2 file.

Exceptions

The parse method might raise 3 exceptions:

1. ParsingException: when the file contains an error and the library can’t interpret the data

2. NotSupportedYetException: when the library doesn’t support the feature yet

3. IntegrityException: when the control totals or the number of objects reported in the trailers don’t match the ones in the file.

Incongruences

We’ve noticed that different banks implement the specs in slightly different ways and the parse method might therefore raise an ParsingException. It is expected to work correctly with files produced by NatWest, RBS, and JP Morgan.

We don’t know yet how to deal with these cases as we don’t have access to many bai2 files so we can’t test it as we would like. You can help by submitting pull requests with sample bai2 files.

For parsing custom transaction type codes that are specific to your use case, you can try overriding the default set:

from bai2.constants import TypeCodes, TypeCode, TypeCodeLevel, TypeCodeTransaction

TypeCodes['299'] = TypeCode('299', TypeCodeTransaction.credit, TypeCodeLevel.detail, 'Custom transaction')

Development

Please report bugs and open pull requests on GitHub. Please add an item to the History section to explain code changes.

To work on changes to this library, it’s recommended to install it in editable mode into a virtual environment, i.e. pip install --editable .

Use python -m tests to run all tests locally. Alternatively, you can use tox if you have multiple python versions.

[Only for GitHub team members] Distribute a new version to PyPI by:

• updating the VERSION tuple in bai2/__init__.py

• adding a note to the History

• publishing a release on GitHub which triggers an upload to PyPI; alternatively, run python -m build; twine upload dist/* locally

History

0.15.0 (2025-11-04)

Testing on python 3.10 to 3.14. Improve linting and modernise code style. Migrated to trusted publishing.

0.14.0 (2024-04-04)

Adds support for charitable organizations/Donor Advised Funds codes 706 and 708 (thanks @coop-nfg).

0.13.0 (2024-01-16)

Parse bai2 files with empty lines, trailing whitespace (thanks @Isaben).

0.12.0 (2023-11-16)

Migrated test, build and release processes away from deprecated setuptools commands. No significant library changes.

0.11.0 (2023-02-17)

Adds support for Real Time Payment detail codes 158 and 458 (thanks @LSakey).

0.10.0 (2023-02-16)

Improve parsing of account identifier records with respect to varying number of commas used by different banks (thanks @forforeach).

0.9.2 (2023-01-13)

Maintenance release, no library changes.

0.9.1 (2022-12-22)

Add support for 829 ‘SEPA Payments’ type code (thanks @podj).

0.9.0 (2022-12-21)

More lenient parsing where integers are expected (thanks @daniel-butler). Add support for 827 & 828 ‘SEPA Payments’ type codes (thanks @podj). Remove testing for python versions below 3.7 (the library is still likely to work with 3.6). Add testing for python 3.11.

0.8.2 (2022-01-26)

No library changes. Add testing for python 3.9 and 3.10.

0.8.0 (2020-11-11)

Remove support for python versions below 3.6.

0.7.0 (2019-10-03)

rows no longer required in BAI2 models (c.f. issue 12 and PR 13).

0.6.0 (2019-09-18)

Fix regular expression escaping. Add python 3.7 testing.

0.5.0 (2018-03-05)

Updated packaging details and improved python version compatibility.

0.1.0 (2015-08-06)

Original release.

Copyright

Copyright (C) 2025 HM Government (Ministry of Justice Digital & Technology). See LICENSE.txt for further details.