computus 1.1.0

Historical chronology tools (indiction, calendar systems, etc.)

Computus

A small Python library and command line tool for historical chronology.

Author

Ivan Debono

Features

• Indiction calculation for Anno Domini/Common Era and Byzantine Anno Mundi years
• Roman numeral conversion in both directions
• Julian and Gregorian calendar conversion
• Gregorian, Julian, and Orthodox Easter calculation
• Era conversion between AD/CE, BC/BCE, Byzantine AM, and AUC
• Simple historical date parsing

Installation

Using pip

pip install computus

Using uv

uv add computus

Or:

uv pip install computus

Usage (Python)

from computus import (
    arabic_to_roman,
    convert_era,
    easter,
    indiction,
    julian_to_gregorian,
    parse_historical_date,
    roman_to_arabic,
)

i = indiction(525)
print(i)                    # 3
print(arabic_to_roman(i))   # III

print(indiction(6033, "AM"))                # 3
print(convert_era(525, "AD", "AM"))         # 6033
print(julian_to_gregorian(1582, 10, 4))     # (1582, 10, 14)
print(easter(2024, "orthodox"))             # (2024, 5, 5)
print(roman_to_arabic("XLII"))              # 42
print(parse_historical_date("15 March 44 BC"))

Command Line Usage

The original short form still calculates an AD indiction:

computus 525

Example output:

Indiction: 3 (III)

Subcommands expose the full toolset:

computus indiction 6033 --calendar AM
computus roman XLII
computus roman 42
computus easter 2024 --calendar orthodox
computus convert 525 --from AD --to AM
computus calendar 1582 10 4 --from julian --to gregorian
computus parse "15 March 44 BC"

Historical Notes

calendar="AD" and calendar="CE" treat the input year as an Anno Domini/Common Era year. calendar="AM" treats the input year as a Byzantine Anno Mundi year directly. To convert an AD year to Byzantine AM first, use convert_era(year, "AD", "AM").

The library uses traditional historical year numbering: there is no year 0. Use BC/BCE era conversion for years before AD 1.

Development

python -m pip install -e ".[dev]"
pytest

License

PolyForm Noncommercial License 1.0.0

Copyright (c) 2026 Ivan Debono