Âm Lịch Việt Nam - Vietnamese Lunar Calendar for Python 🇻🇳

Goal: lightweight - typed - dependency-free - accurate - easy to trust

lunar-vn is designed for:

• Vietnamese calendar apps
• Tết and lunar holiday reminders
• HR, payroll, booking, and event systems
• Bots that need Vietnamese lunar dates
• Cultural, astrology, and Can Chi applications
• Backend services that need a small, typed, no-dependency package
• Personal and business systems that need predictable calendar behavior

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Features

• No Dependencies: Small package with strict typing support (PEP-561 compliant).
• Production-friendly: Deterministic local functions with no runtime service dependency.
• Support Can Chi: Heavenly Stems and Earthly Branches for year, month, day, hour.
• Vietnamese Holidays: Common solar and lunar holidays included.
• Holiday Lists: Get year-specific Vietnamese holiday dates for app and reminder workflows.
• Convert Solar → Lunar: Accepts robust datetime.date inputs.
• Convert Lunar → Solar: Accurate conversion using the Ho Ngoc Duc algorithm.
• Supported Range: Solar dates from 1900-01-01 to 2100-12-31.
• Leap month support: Handled automatically.
• Timezone support: Default UTC+7 (Vietnam).
• Full-range tested: The test suite roundtrips every supported solar date.
• Processing Time Benchmark: High-performance conversions using internal caching (clear_cache supported).

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Installation

pip install lunar-vn

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Usage Examples

Basic Conversion

import datetime as dt
from lunar_vn import solar_to_lunar, lunar_to_solar, LunarDate

# Vietnamese Lunar New Year 2026
solar_date = dt.date(2026, 2, 17)
lunar_date = solar_to_lunar(solar_date)

print(lunar_date) # LunarDate(day=1, month=1, year=2026, leap=False)

# Lunar -> Solar
print(lunar_to_solar(LunarDate(1, 1, 2026))) # 2026-02-17

Get today's Vietnamese lunar date

import datetime as dt
from lunar_vn import solar_to_lunar

today = dt.date.today()
lunar = solar_to_lunar(today)

print(f"Solar: {today}")
print(f"Lunar: {lunar.day}/{lunar.month}/{lunar.year}")
print(f"Leap month: {lunar.leap}")

Can Chi and Holidays

from lunar_vn import solar_to_lunar, can_chi, holidays, list_holidays
import datetime as dt

date = dt.date(2024, 2, 10)
lunar = solar_to_lunar(date)

# Get Year Can Chi
print(can_chi.get_year_can_chi(lunar.year))  # Giáp Thìn

# Get Day Can Chi (requires JDN)
from lunar_vn import jd_from_date
jdn = jd_from_date(date.day, date.month, date.year)
print(can_chi.get_day_can_chi(jdn))  # Giáp Thìn

# Check for Holiday
print(holidays.get_holiday(date))  # Tết Nguyên Đán

# List holidays observed in a Gregorian year
for solar_date, name in list_holidays(2026):
    print(solar_date, name)

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Vietnamese Holidays

lunar-vn includes common Vietnamese solar and lunar holidays.

Solar holidays include:

• Tết Dương Lịch
• Ngày Lễ Tình Nhân (Valentine)
• Ngày Quốc Tế Phụ Nữ
• Ngày Giải Phóng Miền Nam
• Ngày Quốc Tế Lao Động
• Ngày Quốc Tế Thiếu Nhi
• Ngày Quốc Khánh
• Ngày Phụ Nữ Việt Nam
• Ngày Nhà Giáo Việt Nam
• Ngày Thành Lập Quân Đội Nhân Dân Việt Nam
• Lễ Giáng Sinh

Lunar holidays include:

• Tết Nguyên Đán
• Rằm Tháng Giêng
• Tết Hàn Thực
• Giỗ Tổ Hùng Vương
• Lễ Phật Đản
• Tết Đoan Ngọ
• Lễ Thất Tịch
• Lễ Vu Lan
• Tết Trung Thu
• Tết Hạ Nguyên
• Tết Ông Công Ông Táo

Generic lunar reminders are also returned for non-leap months:

• Mùng 1
• Rằm

Specific lunar holidays still take precedence over these reminders.

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Benchmark

To run the benchmark script:

PYTHONPATH=src python3 scripts/benchmark.py

Expected: > 100,000 conversions per second.

When installed as a package, python scripts/benchmark.py also works.

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Accuracy and Scope

lunar-vn focuses on the core Vietnamese lunar calendar use case: conversion, Can Chi naming, and common holiday lookup. It intentionally avoids broader Vạn Sự, astrology, and auspicious-day features so the API stays small and easy to verify.

The supported solar date range is 1900-01-01 through 2100-12-31. The test suite includes an exhaustive solar → lunar → solar roundtrip across that full range.

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Comparison with Chinese Lunar Calendar

See documentation.

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Attribution

The Vietnamese lunar calendar algorithm is described by Ho Ngoc Duc on: https://xemamlich.uhm.vn

This library is a Python re-implementation of the published algorithm.

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License

MIT License.