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Add docstring examples for Scalar temporal functions #1424

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220 changes: 212 additions & 8 deletions python/datafusion/functions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1162,6 +1162,20 @@ def now() -> Expr:
"""Returns the current timestamp in nanoseconds.

This will use the same value for all instances of now() in same statement.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": [1]})
>>> result = df.select(
... dfn.functions.now().alias("now")
... )

Use .value instead of .as_py() because nanosecond timestamps
require pandas to convert to Python datetime objects.

>>> result.collect_column("now")[0].value > 0
True
"""
return Expr(f.now())

Expand Down Expand Up @@ -1222,6 +1236,18 @@ def to_timestamp(arg: Expr, *formatters: Expr) -> Expr:
For usage of ``formatters`` see the rust chrono package ``strftime`` package.

[Documentation here.](https://docs.rs/chrono/latest/chrono/format/strftime/index.html)

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-01-01T00:00:00"]})
>>> result = df.select(
... dfn.functions.to_timestamp(
... dfn.col("a")
... ).alias("ts")
... )
>>> str(result.collect_column("ts")[0].as_py())
'2021-01-01 00:00:00'
"""
return Expr(f.to_timestamp(arg.expr, *_unwrap_exprs(formatters)))

Expand All @@ -1230,6 +1256,18 @@ def to_timestamp_millis(arg: Expr, *formatters: Expr) -> Expr:
"""Converts a string and optional formats to a ``Timestamp`` in milliseconds.

See :py:func:`to_timestamp` for a description on how to use formatters.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-01-01T00:00:00"]})
>>> result = df.select(
... dfn.functions.to_timestamp_millis(
... dfn.col("a")
... ).alias("ts")
... )
>>> str(result.collect_column("ts")[0].as_py())
'2021-01-01 00:00:00'
"""
return Expr(f.to_timestamp_millis(arg.expr, *_unwrap_exprs(formatters)))

Expand All @@ -1238,6 +1276,18 @@ def to_timestamp_micros(arg: Expr, *formatters: Expr) -> Expr:
"""Converts a string and optional formats to a ``Timestamp`` in microseconds.

See :py:func:`to_timestamp` for a description on how to use formatters.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-01-01T00:00:00"]})
>>> result = df.select(
... dfn.functions.to_timestamp_micros(
... dfn.col("a")
... ).alias("ts")
... )
>>> str(result.collect_column("ts")[0].as_py())
'2021-01-01 00:00:00'
"""
return Expr(f.to_timestamp_micros(arg.expr, *_unwrap_exprs(formatters)))

Expand All @@ -1246,6 +1296,18 @@ def to_timestamp_nanos(arg: Expr, *formatters: Expr) -> Expr:
"""Converts a string and optional formats to a ``Timestamp`` in nanoseconds.

See :py:func:`to_timestamp` for a description on how to use formatters.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-01-01T00:00:00"]})
>>> result = df.select(
... dfn.functions.to_timestamp_nanos(
... dfn.col("a")
... ).alias("ts")
... )
>>> str(result.collect_column("ts")[0].as_py())
'2021-01-01 00:00:00'
"""
return Expr(f.to_timestamp_nanos(arg.expr, *_unwrap_exprs(formatters)))

Expand All @@ -1254,69 +1316,198 @@ def to_timestamp_seconds(arg: Expr, *formatters: Expr) -> Expr:
"""Converts a string and optional formats to a ``Timestamp`` in seconds.

See :py:func:`to_timestamp` for a description on how to use formatters.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-01-01T00:00:00"]})
>>> result = df.select(
... dfn.functions.to_timestamp_seconds(
... dfn.col("a")
... ).alias("ts")
... )
>>> str(result.collect_column("ts")[0].as_py())
'2021-01-01 00:00:00'
"""
return Expr(f.to_timestamp_seconds(arg.expr, *_unwrap_exprs(formatters)))


def to_unixtime(string: Expr, *format_arguments: Expr) -> Expr:
"""Converts a string and optional formats to a Unixtime."""
"""Converts a string and optional formats to a Unixtime.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["1970-01-01T00:00:00"]})
>>> result = df.select(dfn.functions.to_unixtime(dfn.col("a")).alias("u"))
>>> result.collect_column("u")[0].as_py()
0
"""
return Expr(f.to_unixtime(string.expr, *_unwrap_exprs(format_arguments)))


def current_date() -> Expr:
"""Returns current UTC date as a Date32 value."""
"""Returns current UTC date as a Date32 value.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": [1]})
>>> result = df.select(
... dfn.functions.current_date().alias("d")
... )
>>> result.collect_column("d")[0].as_py() is not None
True
"""
return Expr(f.current_date())


today = current_date


def current_time() -> Expr:
"""Returns current UTC time as a Time64 value."""
"""Returns current UTC time as a Time64 value.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": [1]})
>>> result = df.select(
... dfn.functions.current_time().alias("t")
... )

Use .value instead of .as_py() because nanosecond timestamps
require pandas to convert to Python datetime objects.

>>> result.collect_column("t")[0].value > 0
True
"""
return Expr(f.current_time())


def datepart(part: Expr, date: Expr) -> Expr:
"""Return a specified part of a date.

This is an alias for :py:func:`date_part`.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-07-15T00:00:00"]})
>>> df = df.select(dfn.functions.to_timestamp(dfn.col("a")).alias("a"))
>>> result = df.select(
... dfn.functions.datepart(dfn.lit("month"), dfn.col("a")).alias("m"))
>>> result.collect_column("m")[0].as_py()
7
"""
return date_part(part, date)


def date_part(part: Expr, date: Expr) -> Expr:
"""Extracts a subfield from the date."""
"""Extracts a subfield from the date.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-07-15T00:00:00"]})
>>> df = df.select(dfn.functions.to_timestamp(dfn.col("a")).alias("a"))
>>> result = df.select(
... dfn.functions.date_part(dfn.lit("year"), dfn.col("a")).alias("y"))
>>> result.collect_column("y")[0].as_py()
2021
"""
return Expr(f.date_part(part.expr, date.expr))


def extract(part: Expr, date: Expr) -> Expr:
"""Extracts a subfield from the date.

This is an alias for :py:func:`date_part`.
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@kosiew kosiew Mar 13, 2026

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datepart, extract, and datetrunc are aliases, but each now carries its own full doctest.

I think setting up one example would risk of docs drift between the canonical function and its alias.


Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-07-15T00:00:00"]})
>>> df = df.select(dfn.functions.to_timestamp(dfn.col("a")).alias("a"))
>>> result = df.select(
... dfn.functions.extract(dfn.lit("day"), dfn.col("a")).alias("d"))
>>> result.collect_column("d")[0].as_py()
15
"""
return date_part(part, date)


def date_trunc(part: Expr, date: Expr) -> Expr:
"""Truncates the date to a specified level of precision."""
"""Truncates the date to a specified level of precision.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-07-15T12:34:56"]})
>>> df = df.select(dfn.functions.to_timestamp(dfn.col("a")).alias("a"))
>>> result = df.select(
... dfn.functions.date_trunc(
... dfn.lit("month"), dfn.col("a")
... ).alias("t")
... )
>>> str(result.collect_column("t")[0].as_py())
'2021-07-01 00:00:00'
"""
return Expr(f.date_trunc(part.expr, date.expr))


def datetrunc(part: Expr, date: Expr) -> Expr:
"""Truncates the date to a specified level of precision.

This is an alias for :py:func:`date_trunc`.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": ["2021-07-15T12:34:56"]})
>>> df = df.select(dfn.functions.to_timestamp(dfn.col("a")).alias("a"))
>>> result = df.select(
... dfn.functions.datetrunc(
... dfn.lit("year"), dfn.col("a")
... ).alias("t")
... )
>>> str(result.collect_column("t")[0].as_py())
'2021-01-01 00:00:00'
"""
return date_trunc(part, date)


def date_bin(stride: Expr, source: Expr, origin: Expr) -> Expr:
"""Coerces an arbitrary timestamp to the start of the nearest specified interval."""
"""Coerces an arbitrary timestamp to the start of the nearest specified interval.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> result = ctx.sql(
... "SELECT date_bin(interval '1 day',"
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@kosiew kosiew Mar 13, 2026

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It would be more consistent to use
dfn.functions.date_bin
here

... " timestamp '2021-07-15 12:34:56',"
... " timestamp '2021-01-01') as b"
... )
>>> str(result.collect_column("b")[0].as_py())
'2021-07-15 00:00:00'
"""
return Expr(f.date_bin(stride.expr, source.expr, origin.expr))


def make_date(year: Expr, month: Expr, day: Expr) -> Expr:
"""Make a date from year, month and day component parts."""
"""Make a date from year, month and day component parts.

Examples:
---------
>>> from datetime import date
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"y": [2024], "m": [1], "d": [15]})
>>> result = df.select(
... dfn.functions.make_date(dfn.col("y"), dfn.col("m"),
... dfn.col("d")).alias("dt"))
>>> result.collect_column("dt")[0].as_py()
datetime.date(2024, 1, 15)
"""
return Expr(f.make_date(year.expr, month.expr, day.expr))


Expand Down Expand Up @@ -1393,7 +1584,20 @@ def named_struct(name_pairs: list[tuple[str, Expr]]) -> Expr:


def from_unixtime(arg: Expr) -> Expr:
"""Converts an integer to RFC3339 timestamp format string."""
"""Converts an integer to RFC3339 timestamp format string.

Examples:
---------
>>> ctx = dfn.SessionContext()
>>> df = ctx.from_pydict({"a": [0]})
>>> result = df.select(
... dfn.functions.from_unixtime(
... dfn.col("a")
... ).alias("ts")
... )
>>> str(result.collect_column("ts")[0].as_py())
'1970-01-01 00:00:00'
"""
return Expr(f.from_unixtime(arg.expr))

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@kosiew kosiew Mar 13, 2026

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The PR title is Add docstring examples for scalar temporal functions, but to_date, to_time, and to_local_time still have no examples. Since those are public temporal wrappers in the same section, this feels incomplete.


Expand Down
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