uk-bank-statement-anonymiser 0.1.4

Anonymise UK bank statement PDFs by scrambling personal data while preserving document structure.

uk-bank-statement-anonymiser

Anonymise UK bank statement PDFs by scrambling personal data while preserving the document's visual structure and layout. All letters in transaction descriptions are replaced with random alternatives; dates, payment codes, protected phrases, and numeric identifiers (sort codes, account numbers, IBANs, card numbers) are handled deterministically so the anonymised output remains internally consistent across pages.

Supported statement types

• HSBC UK current account
• HSBC UK savings account
• Natwest current account
• TSB Spend & Save account
• TSB credit card

Other UK bank PDFs may work, but have not been tested.

Requirements

• Python 3.14+
• pikepdf (installed automatically)

Installation

pip install uk-bank-statement-anonymiser

Quick start

By default, the library automatically detects and anonymises dates, sort codes, account numbers, card numbers, and other sensitive patterns. For custom rules—to force specific replacements or protect additional phrases—see User config files below.

from bank_statement_anonymiser import anonymise_pdf

# Minimal — output written alongside input as "anonymised_<original_name>.pdf"
anonymise_pdf("statement.pdf")

# Explicit output path (recommended — avoids exposing the original filename)
anonymise_pdf("statement.pdf", "safe_output_name.pdf")

User config files

The library ships two system config files (bundled in the package, committed to source control) that cover common protected phrases and known numeric patterns:

File	Purpose
always_anonymise_system.toml	Force specific strings to a known replacement value
never_anonymise_system.toml	Protect specific phrases from being scrambled

You can supplement these with your own files passed as arguments to anonymise_pdf:

anonymise_pdf(
    "statement.pdf",
    "output.pdf",
    always_anonymise_path="my_always_anonymise.toml",
    never_anonymise_path="my_never_anonymise.toml",
)

System config provides defaults; your custom config overrides or extends them. For always_anonymise: your rules win on any clash. For never_anonymise: both system and user lists are combined (union).

User config files should not be committed to source control — they will typically contain real account numbers, sort codes, or names that you are trying to protect.

always_anonymise.toml format

# Force exact string replacements before the scramble pass.
# User file wins over system file on a clash.

"40-37-28" = "00-00-00"
"12345678" = "00000000"
"Jason Farrar" = "John Doe"

never_anonymise.toml format

# Phrases listed here are left exactly as-is during the scramble pass.
# Matching is case-insensitive and whitespace-insensitive.

exclude = [
    "My Bank",
    "My Employer Ltd",
]

API reference

anonymise_pdf

def anonymise_pdf(
    input_path: str | Path,
    output_path: str | Path | None = None,
    always_anonymise_path: str | Path | None = None,
    never_anonymise_path: str | Path | None = None,
    debug: bool = False,
) -> Path

Anonymises a single PDF and returns the path to the output file.

Parameter	Description
input_path	Path to the input PDF
output_path	Path for the output PDF. If omitted, writes anonymised_<stem><suffix> in the same directory as the input
always_anonymise_path	Path to a user always_anonymise.toml (optional)
never_anonymise_path	Path to a user never_anonymise.toml (optional)
debug	Print diagnostic information to stdout when True
Returns	Path to the output PDF file

How it works

The anonymiser works in three steps:

1. Identify sensitive data — Detects sort codes, account numbers, IBANs, card numbers, and other patterns defined in config. Each gets a deterministic fake replacement (e.g. 40-37-28 → 28-28-28 — last two digits repeated). This ensures the same data point is always replaced with the same fake value, even across multiple pages.

2. Protect structural text — Dates, payment type codes, bank URLs, and any phrases in your never_anonymise config are left unchanged. This preserves the document's readability and structure.

3. Scramble remaining text — All other letters are scrambled (e.g. Barclays → Dqhyqbvd), while digits and symbols stay intact. The PDF's layout, fonts, images, and line breaks remain unchanged.

Licence

MIT — see LICENSE.