Conversion Functions

The library provides two utility functions for converting between Anno Domini (AD/Gregorian) and Bikram Sambat (BS/Nepali) dates.

Import

from nepali_date_library import ADtoBS, BStoAD

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ADtoBS()

Converts an Anno Domini (AD) date to a Bikram Sambat (BS) date.

Signature

def ADtoBS(adDate: str) -> str:

Parameters

Parameter	Type	Description
adDate	str	AD date in YYYY-MM-DD format

Returns

str - BS date in YYYY-MM-DD format

Example

from nepali_date_library import ADtoBS

# Convert Gregorian date to Nepali date
bs_date = ADtoBS("2026-01-14")
print(bs_date) # '2082-10-01'

# More examples
print(ADtoBS("2024-04-13")) # '2080-12-31' (Last day of 2080)
print(ADtoBS("2024-04-14")) # '2081-01-01' (Nepali New Year 2081)
print(ADtoBS("2025-04-14")) # '2082-01-01' (Nepali New Year 2082)

Error Handling

The function raises an error in the following cases:

# Invalid format
try:
    ADtoBS("2026/01/14") # Wrong separator
except ValueError as e:
    print(e) # Invalid date format. Expected format: YYYY-MM-DD

# Invalid date
try:
    ADtoBS("2026-13-01") # Invalid month
except ValueError as e:
    print(e) # Invalid date provided

# Out of range
try:
    ADtoBS("1940-01-01") # Before supported range
except ValueError as e:
    print(e) # Failed to convert AD to BS

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BStoAD()

Converts a Bikram Sambat (BS) date to an Anno Domini (AD) date.

Signature

def BStoAD(bsDate: str) -> str:

Parameters

Parameter	Type	Description
bsDate	str	BS date in YYYY-MM-DD format

Returns

str - AD date in YYYY-MM-DD format

Example

from nepali_date_library import BStoAD

# Convert Nepali date to Gregorian date
ad_date = BStoAD("2082-10-01")
print(ad_date) # '2026-01-14'

# More examples
print(BStoAD("2081-01-01")) # '2024-04-14' (Nepali New Year 2081)
print(BStoAD("2082-01-01")) # '2025-04-14' (Nepali New Year 2082)
print(BStoAD("2080-12-31")) # '2024-04-13'

Error Handling

# Invalid format
try:
    BStoAD("2082/10/01") # Wrong separator
except ValueError as e:
    print(e) # Invalid date format. Expected format: YYYY-MM-DD

# Out of range
try:
    BStoAD("1975-01-01") # Before BS 1976
except ValueError as e:
    print(e) # Invalid date provided or out of range

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Supported Date Range

Both conversion functions work within the following range:

Calendar	Start	End
Bikram Sambat (BS)	1976-01-01	2100-12-30
Anno Domini (AD)	1919-04-13	~2044-04

Dates outside this range may raise a ValueError.

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Using with NepaliDate Class

You can also perform conversions using the NepaliDate class:

from datetime import datetime
from nepali_date_library import NepaliDate

# AD to BS using constructor
ad_datetime = datetime(2026, 1, 14)
nepali_date = NepaliDate(ad_datetime)
print(nepali_date.format("YYYY-MM-DD")) # 2082-10-01

# BS to AD using get_english_date()
bs_date = NepaliDate("2082-10-01")
ad_datetime = bs_date.get_english_date()
print(ad_datetime.strftime("%Y-%m-%d")) # 2026-01-14

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Common Patterns

Batch Conversion

from nepali_date_library import ADtoBS

ad_dates = ["2026-01-14", "2026-02-15", "2026-03-16"]
bs_dates = [ADtoBS(date) for date in ad_dates]
print(bs_dates)
# ['2082-10-01', '2082-11-03', '2082-12-03']

Safe Conversion with Error Handling

from nepali_date_library import ADtoBS

def safe_ad_to_bs(ad_date: str) -> str:
    try:
        return ADtoBS(ad_date)
    except ValueError:
        return None

print(safe_ad_to_bs("2026-01-14")) # '2082-10-01'
print(safe_ad_to_bs("invalid"))    # None