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from __future__ import annotations from typing import TYPE_CHECKING, Generic, TypeVar if TYPE_CHECKING: from narwhals.expr import Expr ExprT = TypeVar("ExprT", bound="Expr") class ExprStructNamespace(Generic[ExprT]): def __init__(self, expr: ExprT) -> None: self._expr = expr def field(self, name: str) -> ExprT: r"""Retrieve a Struct field as a new expression. Arguments: name: Name of the struct field to retrieve. Returns: A new expression. Examples: >>> import polars as pl >>> import narwhals as nw >>> df_native = pl.DataFrame( ... {"user": [{"id": "0", "name": "john"}, {"id": "1", "name": "jane"}]} ... ) >>> df = nw.from_native(df_native) >>> df.with_columns(name=nw.col("user").struct.field("name")) ┌───────────────────────┐ | Narwhals DataFrame | |-----------------------| |shape: (2, 2) | |┌──────────────┬──────┐| |│ user ┆ name │| |│ --- ┆ --- │| |│ struct[2] ┆ str │| |╞══════════════╪══════╡| |│ {"0","john"} ┆ john │| |│ {"1","jane"} ┆ jane │| |└──────────────┴──────┘| └───────────────────────┘ """ return self._expr._with_elementwise_op( lambda plx: self._expr._to_compliant_expr(plx).struct.field(name) )