dont forget the utils file

polars_xdt/utils.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+import polars as pl
+
+if TYPE_CHECKING:
+    from polars.type_aliases import IntoExpr, PolarsDataType
+
+
+def parse_into_expr(
+    expr: IntoExpr,
+    *,
+    str_as_lit: bool = False,
+    list_as_lit: bool = True,
+    dtype: PolarsDataType | None = None,
+) -> pl.Expr:
+    """
+    Parse a single input into an expression.
+
+    Parameters
+    ----------
+    expr
+        The input to be parsed as an expression.
+    str_as_lit
+        Interpret string input as a string literal. If set to `False` (default),
+        strings are parsed as column names.
+    list_as_lit
+        Interpret list input as a lit literal, If set to `False`,
+        lists are parsed as `Series` literals.
+    dtype
+        If the input is expected to resolve to a literal with a known dtype, pass
+        this to the `lit` constructor.
+
+    Returns
+    -------
+    polars.Expr
+    """
+    if isinstance(expr, pl.Expr):
+        pass
+    elif isinstance(expr, str) and not str_as_lit:
+        expr = pl.col(expr)
+    elif isinstance(expr, list) and not list_as_lit:
+        expr = pl.lit(pl.Series(expr), dtype=dtype)
+    else:
+        expr = pl.lit(expr, dtype=dtype)
+
+    return expr