opensalestax-python

Python SDK for OpenSalesTax — calculate US sales tax via the engine's v1 HTTP API.

A thin, well-typed wrapper around the engine's four endpoints. Used by the OpenSalesTax connectors for Odoo and ERPNext, and suitable for any Python application that needs destination-based US sales-tax calculation.

Install

pip install opensalestax

Requires Python 3.10+.

Quickstart

from decimal import Decimal
from opensalestax import OpenSalesTaxClient, Address, LineItem

with OpenSalesTaxClient(base_url="http://localhost:8080") as client:
    result = client.calculate(
        address=Address(zip5="55401"),  # Minneapolis, MN
        line_items=[
            LineItem(amount=Decimal("100.00"), category="general"),
        ],
    )

    print(f"Subtotal:  ${result.subtotal}")
    print(f"Tax:       ${result.tax_total}")
    for line in result.lines:
        for j in line.jurisdictions:
            print(f"  {j.name} ({j.type}) {j.rate_pct}%: ${j.tax}")

Output (against engine v0.54+):

Subtotal:  $100.00
Tax:       $9.0250
  Minneapolis (city) 0.50000%: $0.5000
  Hennepin County (county) 0.15000%: $0.1500
  Minnesota (state) 6.87500%: $6.8750
  Hennepin County Transit Sales Tax (district) 0.50000%: $0.5000
  Metro Area Transportation Sales Tax (district) 0.75000%: $0.7500
  Metro Area Sales and Use Tax for Housing (district) 0.25000%: $0.2500

API

OpenSalesTaxClient

OpenSalesTaxClient(
    base_url: str,                    # engine URL, e.g. "http://localhost:8080"
    api_key: str | None = None,       # optional Bearer token
    timeout: float = 10.0,            # seconds
    user_agent: str | None = None,    # appended to default UA
    verify: bool = True,              # TLS verification
)

Use as a context manager (recommended) or call client.close() manually.

Methods

Models

All models are immutable (frozen=True) Pydantic v2. Money and rates use decimal.Decimal to preserve precision; rates are expressed as percents (e.g. Decimal("6.875") means 6.875%).

• Address(zip5, zip4=None) — engine v1 is ZIP-only
• LineItem(amount, category="general") — pre-tax amount as Decimal
• JurisdictionBreakdown(name, type, rate_pct, tax) — one taxing authority
• CalculatedLine(amount, category, tax, rate_pct, jurisdictions, note)
• CalculationResult(subtotal, tax_total, lines, disclaimer)
• RateStack(input, jurisdictions, combined_rate_pct, disclaimer)
• HealthResponse(status, version, database_connected)
• StateCoverage(abbrev, name, has_sales_tax, sst_member, tier, notes)

Errors

Flat hierarchy — connectors typically catch one or two:

from opensalestax import (
    OpenSalesTaxError,            # base class
    OpenSalesTaxNetworkError,     # timeout, connection refused, DNS, TLS
    OpenSalesTaxAPIError,         # non-2xx HTTP response (.status_code, .response_body)
    OpenSalesTaxValidationError,  # response shape didn't match SDK models
    NonUSDError,                  # non-USD or non-US address
)

Recommended pattern in a connector:

try:
    result = client.calculate(address=addr, line_items=items)
except OpenSalesTaxNetworkError:
    fall_back_to_catalog_rate()      # engine unreachable
except OpenSalesTaxAPIError as e:
    if e.status_code >= 500:
        fall_back_to_catalog_rate()  # engine glitch
    else:
        surface_to_merchant(e)       # 4xx — config / data issue

Compatibility

The engine's v1 HTTP API is the contract. Internal Python modules are not — connectors must use this SDK or call the HTTP API directly.

Calculation only

Tax calculations are provided as-is for convenience. The merchant is solely responsible for tax-collection accuracy and remittance to the appropriate jurisdictions. Verify against your state Department of Revenue before remitting.

This SDK does not:

• File tax returns or remit collected tax (engine constitution §13)
• Validate addresses
• Cache calculations (caller's responsibility — caching policy is platform-specific)
• Retry transient errors (caller's responsibility)

Connectors that use this SDK

• ejosterberg/opensalestax-odoo — Odoo Community 16.0/17.0/18.0 connector
• (ERPNext connector planned)

Development

git clone https://github.com/ejosterberg/opensalestax-python.git
cd opensalestax-python
uv venv
uv pip install -e ".[dev]"

# Quality gate
ruff check src tests
ruff format --check src tests
mypy --strict src/opensalestax
pytest --cov=opensalestax --cov-fail-under=90

# Live tests against an actual engine (skipped by default)
RUN_LIVE_TESTS=1 OST_BASE_URL=http://localhost:8080 pytest -m live -v

Contributing

See CONTRIBUTING.md. All commits must carry a DCO sign-off (git commit -s). No AI co-author trailers.

License

Apache 2.0. Apache 2.0 + DCO sign-off + SPDX header on every source file.