Python Pandas - Return the frequency object from the PeriodIndex object

The PeriodIndex.freq property in Pandas returns the frequency object associated with a PeriodIndex. This property is useful for understanding the time interval pattern of your period data.

What is PeriodIndex?

A PeriodIndex is an immutable array that holds ordinal values representing regular periods in time. Each period represents a span of time (like a day, month, or year) rather than a specific timestamp.

Creating a PeriodIndex with Frequency

When creating a PeriodIndex, you specify the frequency using the freq parameter ?

import pandas as pd

# Create a PeriodIndex with daily frequency
periodIndex = pd.PeriodIndex(['2021-09-25', '2019-10-30', '2020-11-20',
                              '2021-07-15', '2022-06-12', '2023-07-10'], freq="D")

print("PeriodIndex:")
print(periodIndex)

PeriodIndex:
PeriodIndex(['2021-09-25', '2019-10-30', '2020-11-20', '2021-07-15', '2022-06-12', '2023-07-10'], dtype='period[D]')

Accessing the Frequency Object

Use the freq property to retrieve the frequency object ?

import pandas as pd

periodIndex = pd.PeriodIndex(['2021-09-25', '2019-10-30', '2020-11-20',
                              '2021-07-15', '2022-06-12', '2023-07-10'], freq="D")

# Get the frequency object
frequency = periodIndex.freq
print("Frequency object:", frequency)
print("Frequency type:", type(frequency))

Frequency object: <Day>
Frequency type: <class 'pandas._libs.tslibs.offsets.Day'>

Different Frequency Examples

Here are examples with different frequency settings ?

import pandas as pd

# Monthly frequency
monthly_periods = pd.PeriodIndex(['2021-01', '2021-02', '2021-03'], freq="M")
print("Monthly frequency:", monthly_periods.freq)

# Quarterly frequency  
quarterly_periods = pd.PeriodIndex(['2021Q1', '2021Q2', '2021Q3'], freq="Q")
print("Quarterly frequency:", quarterly_periods.freq)

# Yearly frequency
yearly_periods = pd.PeriodIndex(['2021', '2022', '2023'], freq="Y")
print("Yearly frequency:", yearly_periods.freq)

Monthly frequency: <MonthEnd>
Quarterly frequency: <QuarterEnd: startingMonth=12>
Yearly frequency: <YearEnd: month=12>

Common Frequency Codes

Conclusion

The freq property provides access to the frequency object of a PeriodIndex, helping you understand the time interval pattern. This is essential for time series analysis and period-based operations in Pandas.