Polars · Module

.dt.year

Extracts the calendar year from Date or Datetime values. The expression returns Int32 output and can be composed with other Polars expressions.

How it works

Call .dt.year() on a Polars date-time expression to extract the calendar year from each value. It accepts Date and Datetime columns and produces an Int32 expression, which can be used in selections, filters, derived columns, or grouping expressions.

Syntax

Expr.dt.year()

Returns

Expr of data type Int32

Key points

Extracts the calendar year represented by each Date or Datetime value.
Works with both Polars Date and Datetime columns.
Returns the calendar-date year rather than an ISO week-based year.
Produces an Int32-typed expression.

Example: Extract calendar years

import polars as pl
from datetime import date

df = pl.DataFrame({"date": [date(2001, 1, 1), date(2002, 1, 1)]})
result = df.with_columns(
    pl.col("date").dt.year().alias("year")
)
print(result)

Adds a calendar-year column extracted from the Date column.

When to use it

Derive calendar-year features

Create a separate year column from a date or timestamp field.

Filter by year

Keep or exclude records based on their calendar year.

Group temporal data

Build year-based aggregations or grouping keys.

Interview questions

QWhat does Expr.dt.year() return, and which input types does it support?

Expr.dt.year() extracts the year from the underlying Date representation and applies to Date and Datetime columns. The resulting expression has data type Int32.

Follow-up: How would you obtain the ISO week-based year instead? Use the related Expr.dt.iso_year() expression.

QHow is Expr.dt.year() typically used in a DataFrame transformation?

Use it as part of an expression, such as pl.col("date").dt.year(), then alias or otherwise compose that expression. For example, with_columns can materialize the extracted year as a new column.

Follow-up: How could the extracted value be used for filtering? Compose it with a comparison, such as pl.col("date").dt.year() < 1990.

QWhat distinction should you make between dt.year() and dt.iso_year()?

The result is the calendar year represented by each date, not the ISO week-based year. Its output expression is typed as Int32.

Follow-up: Why might calendar and ISO years differ near New Year? ISO week dates can assign boundary days to the adjacent week-based year; use dt.iso_year() when that convention is required.

Expr.dt.iso_year
Expr.dt.month
Expr.dt.quarter
Expr.dt.day

Source: polars.Expr.dt.year. Checked 2026-10-15.