1 files changed, 60 insertions, 0 deletions
diff --git a/venv/lib/python3.8/site-packages/narwhals/_duration.py b/venv/lib/python3.8/site-packages/narwhals/_duration.py
new file mode 100644
index 0000000..87b6d83
--- /dev/null
+++ b/venv/lib/python3.8/site-packages/narwhals/_duration.py
@@ -0,0 +1,60 @@
+"""Tools for working with the Polars duration string language."""
+
+from __future__ import annotations
+
+import re
+from typing import TYPE_CHECKING, Literal, cast, get_args
+
+if TYPE_CHECKING:
+    from typing_extensions import TypeAlias
+
+__all__ = ["IntervalUnit", "parse_interval_string"]
+
+IntervalUnit: TypeAlias = Literal["ns", "us", "ms", "s", "m", "h", "d", "mo", "q", "y"]
+"""A Polars duration string interval unit.
+
+- 'ns': nanosecond.
+- 'us': microsecond.
+- 'ms': millisecond.
+- 's': second.
+- 'm': minute.
+- 'h': hour.
+- 'd': day.
+- 'mo': month.
+- 'q': quarter.
+- 'y': year.
+"""
+
+PATTERN_INTERVAL: re.Pattern[str] = re.compile(
+    r"^(?P<multiple>\d+)(?P<unit>ns|us|ms|mo|m|s|h|d|q|y)\Z"
+)
+MONTH_MULTIPLES = frozenset([1, 2, 3, 4, 6, 12])
+QUARTER_MULTIPLES = frozenset([1, 2, 4])
+
+
+def parse_interval_string(every: str) -> tuple[int, IntervalUnit]:
+    """Parse a string like "1d", "2h", "3m" into a tuple of (number, unit).
+
+    Returns:
+        A tuple of multiple and unit parsed from the interval string.
+    """
+    if match := PATTERN_INTERVAL.match(every):
+        multiple = int(match["multiple"])
+        unit = cast("IntervalUnit", match["unit"])
+        if unit == "mo" and multiple not in MONTH_MULTIPLES:
+            msg = f"Only the following multiples are supported for 'mo' unit: {MONTH_MULTIPLES}.\nGot: {multiple}."
+            raise ValueError(msg)
+        if unit == "q" and multiple not in QUARTER_MULTIPLES:
+            msg = f"Only the following multiples are supported for 'q' unit: {QUARTER_MULTIPLES}.\nGot: {multiple}."
+            raise ValueError(msg)
+        if unit == "y" and multiple != 1:
+            msg = (
+                f"Only multiple 1 is currently supported for 'y' unit.\nGot: {multiple}."
+            )
+            raise ValueError(msg)
+        return multiple, unit
+    msg = (
+        f"Invalid `every` string: {every}. Expected string of kind <number><unit>, "
+        f"where 'unit' is one of: {get_args(IntervalUnit)}."
+    )
+    raise ValueError(msg)