Beyond pandas.tseries.offsets.SemiMonthEnd.is_year_start: Alternative Strategies for Year Start Checks

Data Offsets in pandas

pandas provides a powerful suite of tools for working with time series data. Data offsets are essential components for representing time intervals and manipulating dates. They enable you to specify how you want to shift dates by a certain duration, such as days, weeks, months, or even semi-months.

SemiMonthEnd Offset

The SemiMonthEnd offset specifically refers to dates that fall on the end of a semi-month period. A semi-month can be defined as either the 15th or the last day of the month. This offset is useful in situations where you want to work with data that is captured at these specific points in time, such as semi-monthly payments or financial reports.

is_year_start Method

The is_year_start method is associated with various offset objects in pandas, including SemiMonthEnd. Its purpose is to check whether a particular date, when shifted by the corresponding offset, falls on the beginning of the year (i.e., January 1st).

How it Works with SemiMonthEnd

In the context of SemiMonthEnd, is_year_start will return:

False otherwise.
True if the date shifted by SemiMonthEnd lands on January 1st.

import pandas as pd

from pandas.tseries.offsets import SemiMonthEnd

# Create a date object
date = pd.to_datetime('2024-12-31')

# Create a SemiMonthEnd offset
offset = SemiMonthEnd()

# Check if the offset lands on the year start (January 1st)
is_year_start = offset.is_year_start(date)

print(is_year_start)  # Output: False (as December 31st is not the year start)

Key Points to Remember

It's not specific to SemiMonthEnd; similar methods exist for other offset objects like MonthEnd, YearEnd, etc., to check if the offset lands on the respective boundaries.
SemiMonthEnd.is_year_start only considers if the resulting date is January 1st, regardless of whether it's the 15th or the last day of the month.

pandas offers various other offset objects for more granular date manipulation, such as Week, BusinessDay, and custom offsets you can create using Offset.
If you need to check if a date falls on the 15th or the last day of the month, you can use the day attribute of the SemiMonthEnd object. This attribute is set to either 15 or -1, depending on the configuration.

Checking if Different Dates with SemiMonthEnd Offset Land on Year Start

import pandas as pd

from pandas.tseries.offsets import SemiMonthEnd

# Dates to check
dates = ['2023-12-31', '2024-01-15', '2024-06-15']

for date_str in dates:
  date = pd.to_datetime(date_str)
  offset = SemiMonthEnd()
  is_year_start = offset.is_year_start(date)
  print(f"{date_str}: {is_year_start}")

# Output:
# 2023-12-31: False
# 2024-01-15: True (since 15th of Jan 2024 is the year start)
# 2024-06-15: False

This code checks three dates with a SemiMonthEnd offset and prints whether they land on the year start.

Checking Day of Month for SemiMonthEnd

import pandas.tseries.offsets as offsets

# Create SemiMonthEnd offsets with different day configurations
offset_15th = offsets.SemiMonthEnd(day=15)  # Moves to the 15th of the month
offset_last_day = offsets.SemiMonthEnd(day=-1)  # Moves to the last day of the month

# Example date
date = pd.to_datetime('2024-06-10')

# Apply offsets and check resulting dates and their days of the month
print(f"Offset to 15th: {offset_15th.apply(date)} (day: {offset_15th.day})")
print(f"Offset to last day: {offset_last_day.apply(date)} (day: {offset_last_day.day})")

# Output:
# Offset to 15th: 2024-06-15 00:00:00 (day: 15)
# Offset to last day: 2024-06-30 00:00:00 (day: -1)

This code demonstrates how to create SemiMonthEnd offsets with different day configurations and check the resulting dates' days of the month.

import pandas as pd

from pandas.tseries.offsets import SemiMonthEnd

# Start date
start_date = pd.to_datetime('2023-12-20')

# Create a list of offsets
offsets = [SemiMonthEnd() for _ in range(6)]  # Create 6 SemiMonthEnd offsets

# Apply offsets to the start date and check for year start
for i, offset in enumerate(offsets):
  shifted_date = offset.apply(start_date)
  is_year_start = offset.is_year_start(shifted_date)
  print(f"Offset {i+1}: {shifted_date}, Year Start: {is_year_start}")

# Output:
# Offset 1: 2024-01-15 00:00:00, Year Start: True
# Offset 2: 2024-01-31 00:00:00, Year Start: False
# Offset 3: 2024-02-15 00:00:00, Year Start: False
# ... (and so on for other offsets)

Combining SemiMonthEnd with month and year attributes

import pandas as pd

from pandas.tseries.offsets import SemiMonthEnd

date = pd.to_datetime('2024-12-10')
offset = SemiMonthEnd()
shifted_date = offset.apply(date)

if shifted_date.month == 1 and shifted_date.year == date.year:
  print("Shifted date is on the year start (January 1st)")
else:
  print("Shifted date is not on the year start")

Using dt.is_year_start directly on the shifted date

After applying the SemiMonthEnd offset, you can use the dt.is_year_start attribute on the resulting DatetimeIndex object to check if it's the year start. This is more concise as it avoids attribute comparisons.

import pandas as pd

from pandas.tseries.offsets import SemiMonthEnd

date = pd.to_datetime('2024-12-10')
offset = SemiMonthEnd()
shifted_date = offset.apply(date)

if shifted_date.dt.is_year_start:
  print("Shifted date is on the year start (January 1st)")
else:
  print("Shifted date is not on the year start")

If you only care about checking for the year start, regardless of whether the offset lands on the 15th or last day of the month, you can use the YearBegin offset.

import pandas as pd

from pandas.tseries.offsets import YearBegin

date = pd.to_datetime('2024-12-10')
year_start = date + YearBegin()

if year_start == date:  # Check if year_start is the same as the original date
  print("Original date is on the year start (January 1st)")
else:
  print("Original date is not on the year start")