[Data] Compute Expressions-datetime

[400Ping]

Description

Completing the datetime namespace operations

Related issues

Related to #58674

Additional information

[gemini-code-assist]

Code Review

This pull request introduces datetime expression operations under the .dt namespace, which is a great addition. The implementation in dt_namespace.py is mostly clean and follows existing patterns.

However, there is a critical omission: the dt property is not defined on the Expr class in python/ray/data/expressions.py. Without this, expressions like col('my_date').dt.year() will fail. This property needs to be added, similar to how .list, .str, and .struct are implemented. You can add the following property to the Expr class:

    @property
    def dt(self) -> "_DatetimeNamespace":
        """Access datetime operations for this expression."""
        from ray.data.namespace_expressions.dt_namespace import _DatetimeNamespace

        return _DatetimeNamespace(self)

I've also left a couple of comments in dt_namespace.py regarding potential improvements:

• A high-severity issue with how the return data type is determined for ceil, floor, and round functions, which could lead to incorrect type inference.
• A medium-severity suggestion to refactor duplicated code for better maintainability.