chore: factor out log from SparkLike, DuckDB, and Ibis (#2915)

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: ym-pett

narwhals/_duckdb/expr.py

@@ -292,17 +292,6 @@ def window_f(df: DuckDBLazyFrame, inputs: DuckDBWindowInputs) -> list[Expression
             version=self._version,
         )
 
-    def log(self, base: float) -> Self:
-        def _log(expr: Expression) -> Expression:
-            log = F("log", expr)
-            return (
-                when(expr < lit(0), lit(float("nan")))
-                .when(expr == lit(0), lit(float("-inf")))
-                .otherwise(log / F("log", lit(base)))
-            )
-
-        return self._with_elementwise(_log)
-
     @property
     def str(self) -> DuckDBExprStringNamespace:
         return DuckDBExprStringNamespace(self)

narwhals/_ibis/expr.py

@@ -324,17 +324,6 @@ def _rank(expr: ir.Column) -> ir.Column:
 
         return self._with_callable(_rank)
 
-    def log(self, base: float) -> Self:
-        def _log(expr: ir.NumericColumn) -> ir.Value:
-            otherwise = expr.log(cast("ir.NumericValue", lit(base)))
-            return ibis.cases(
-                (expr < lit(0), lit(float("nan"))),
-                (expr == lit(0), lit(float("-inf"))),
-                else_=otherwise,
-            )
-
-        return self._with_callable(_log)
-
     @property
     def str(self) -> IbisExprStringNamespace:
         return IbisExprStringNamespace(self)

narwhals/_spark_like/expr.py

@@ -377,16 +377,6 @@ def _fill_constant(expr: Column, value: Column) -> Column:
 
         return self._with_elementwise(_fill_constant, value=value)
 
-    def log(self, base: float) -> Self:
-        def _log(expr: Column) -> Column:
-            return (
-                self._F.when(expr < 0, self._F.lit(float("nan")))
-                .when(expr == 0, self._F.lit(float("-inf")))
-                .otherwise(self._F.log(float(base), expr))
-            )
-
-        return self._with_elementwise(_log)
-
     @property
     def str(self) -> SparkLikeExprStringNamespace:
         return SparkLikeExprStringNamespace(self)

narwhals/_sql/expr.py

@@ -510,6 +510,20 @@ def _sqrt(expr: NativeExprT) -> NativeExprT:
     def exp(self) -> Self:
         return self._with_elementwise(lambda expr: self._function("exp", expr))
 
+    def log(self, base: float) -> Self:
+        def _log(expr: NativeExprT) -> NativeExprT:
+            return self._when(
+                expr < self._lit(0),  # type: ignore[operator]
+                self._lit(float("nan")),
+                self._when(
+                    cast("NativeExprT", expr == self._lit(0)),
+                    self._lit(float("-inf")),
+                    self._function("log", expr) / self._function("log", self._lit(base)),  # type: ignore[operator]
+                ),
+            )
+
+        return self._with_elementwise(_log)
+
     # Cumulative
     def cum_sum(self, *, reverse: bool) -> Self:
         return self._with_window_function(self._cum_window_func("sum", reverse=reverse))