RFC: Introduce pandas.col

pandas/__init__.py

@@ -105,6 +105,7 @@
     Series,
     DataFrame,
 )
+from pandas.core.col import col
 
 from pandas.core.dtypes.dtypes import SparseDtype
 
@@ -281,6 +282,7 @@
     "array",
     "arrays",
     "bdate_range",
+    "col",
     "concat",
     "crosstab",
     "cut",

pandas/core/col.py

@@ -0,0 +1,192 @@
+from __future__ import annotations
+
+from collections.abc import (
+    Callable,
+    Hashable,
+)
+from typing import (
+    TYPE_CHECKING,
+    Any,
+)
+
+from pandas.core.series import Series
+
+if TYPE_CHECKING:
+    from pandas import DataFrame
+
+
+def parse_args(df: DataFrame, *args: Any) -> tuple[Series]:
+    return tuple([x._func(df) if isinstance(x, Expr) else x for x in args])
+
+
+def parse_kwargs(df: DataFrame, **kwargs: Any) -> dict[Hashable, Series]:
+    return {
+        key: val._func(df) if isinstance(val, Expr) else val
+        for key, val in kwargs.items()
+    }
+
+
+class Expr:
+    def __init__(self, func: Callable[[DataFrame], Any]) -> None:
+        self._func = func
+
+    def __call__(self, df: DataFrame) -> Series:
+        result = self._func(df)
+        if not isinstance(result, Series):
+            msg = (
+                "Expected function which returns Series, "
+                f"got function which returns: {type(result)}"
+            )
+            raise TypeError(msg)
+        return result
+
+    # namespaces
+    @property
+    def dt(self) -> NamespaceExpr:
+        return NamespaceExpr(self, "dt")
+
+    @property
+    def str(self) -> NamespaceExpr:
+        return NamespaceExpr(self, "str")
+
+    @property
+    def cat(self) -> NamespaceExpr:
+        return NamespaceExpr(self, "cat")
+
+    @property
+    def list(self) -> NamespaceExpr:
+        return NamespaceExpr(self, "list")
+
+    @property
+    def sparse(self) -> NamespaceExpr:
+        return NamespaceExpr(self, "sparse")
+
+    @property
+    def struct(self) -> NamespaceExpr:
+        return NamespaceExpr(self, "struct")
+
+    # Binary ops
+
+    def __add__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__add__(other._func(df)))
+        return Expr(lambda df: self._func(df).__add__(other))
+
+    def __radd__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__radd__(other._func(df)))
+        return Expr(lambda df: self._func(df).__radd__(other))
+
+    def __sub__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__sub__(other._func(df)))
+        return Expr(lambda df: self._func(df).__sub__(other))
+
+    def __rsub__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__rsub__(other._func(df)))
+        return Expr(lambda df: self._func(df).__rsub__(other))
+
+    def __mul__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__mul__(other._func(df)))
+        return Expr(lambda df: self._func(df).__mul__(other))
+
+    def __rmul__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__rmul__(other._func(df)))
+        return Expr(lambda df: self._func(df).__rmul__(other))
+
+    def __truediv__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__truediv__(other._func(df)))
+        return Expr(lambda df: self._func(df).__truediv__(other))
+
+    def __rtruediv__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__rtruediv__(other._func(df)))
+        return Expr(lambda df: self._func(df).__rtruediv__(other))
+
+    def __floordiv__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__floordiv__(other._func(df)))
+        return Expr(lambda df: self._func(df).__floordiv__(other))
+
+    def __rfloordiv__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__rfloordiv__(other._func(df)))
+        return Expr(lambda df: self._func(df).__rfloordiv__(other))
+
+    def __ge__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__ge__(other._func(df)))
+        return Expr(lambda df: self._func(df).__ge__(other))
+
+    def __gt__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__gt__(other._func(df)))
+        return Expr(lambda df: self._func(df).__gt__(other))
+
+    def __le__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__le__(other._func(df)))
+        return Expr(lambda df: self._func(df).__le__(other))
+
+    def __lt__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__lt__(other._func(df)))
+        return Expr(lambda df: self._func(df).__lt__(other))
+
+    def __eq__(self, other: object) -> Expr:  # type: ignore[override]
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__eq__(other._func(df)))
+        return Expr(lambda df: self._func(df).__eq__(other))
+
+    def __ne__(self, other: object) -> Expr:  # type: ignore[override]
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__ne__(other._func(df)))
+        return Expr(lambda df: self._func(df).__ne__(other))
+
+    def __mod__(self, other: Any) -> Expr:
+        if isinstance(other, Expr):
+            return Expr(lambda df: self._func(df).__mod__(other._func(df)))
+        return Expr(lambda df: self._func(df).__mod__(other))
+
+    # Everything else
+
+    # Function "pandas.core.col.Expr.str" is not valid as a type
+    def __getattr__(self, attr: str, /) -> Any:  # type: ignore[valid-type]
+        def func(df: DataFrame, *args: Any, **kwargs: Any) -> Any:
+            parsed_args = parse_args(df, *args)
+            parsed_kwargs = parse_kwargs(df, **kwargs)
+            return getattr(self(df), attr)(*parsed_args, **parsed_kwargs)
+
+        return lambda *args, **kwargs: Expr(lambda df: func(df, *args, **kwargs))
+
+
+class NamespaceExpr:
+    def __init__(self, func: Callable[[DataFrame], Any], namespace: str) -> None:
+        self._func = func
+        self._namespace = namespace
+
+    def __getattr__(self, attr: str) -> Any:
+        if isinstance(getattr(getattr(Series, self._namespace), attr), property):
+            return Expr(
+                lambda df: getattr(getattr(self._func(df), self._namespace), attr)
+            )
+
+        def func(df: DataFrame, *args: Any, **kwargs: Any) -> Any:
+            parsed_args = parse_args(df, *args)
+            parsed_kwargs = parse_kwargs(df, **kwargs)
+            return getattr(getattr(self._func(df), self._namespace), attr)(
+                *parsed_args, **parsed_kwargs
+            )
+
+        return lambda *args, **kwargs: Expr(lambda df: func(df, *args, **kwargs))
+
+
+def col(col_name: Hashable) -> Expr:
+    if not isinstance(col_name, Hashable):
+        msg = f"Expected Hashable, got: {type(col_name)}"
+        raise TypeError(msg)
+    return Expr(lambda df: df[col_name])

pandas/tests/api/test_api.py

@@ -107,6 +107,7 @@ class TestPDApi(Base):
     funcs = [
         "array",
         "bdate_range",
+        "col",
         "concat",
         "crosstab",
         "cut",