[SPARK-49894][PYTHON][CONNECT] Refine the string representation of column field operations

### What changes were proposed in this pull request?
Refine the string representation of column field operations: `GetField`, `WithField`, and `DropFields`

### Why are the changes needed?
make the string representations consistent between pyspark classic and connect

### Does this PR introduce _any_ user-facing change?
yes

before
```
In [1]: from pyspark.sql import functions as sf

In [2]: c = sf.col("c")

In [3]: c.x
Out[3]: Column<'UnresolvedExtractValue(c, x)'>
```

after
```
In [1]: from pyspark.sql import functions as sf

In [2]: c = sf.col("c")

In [3]: c.x
Out[3]: Column<'c['x']'>
```

### How was this patch tested?
added ut

### Was this patch authored or co-authored using generative AI tooling?
no

Closes #48369 from zhengruifeng/py_connect_col_str.

Lead-authored-by: Ruifeng Zheng <[email protected]>
Co-authored-by: Hyukjin Kwon <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>

Author: zhengruifeng

python/pyspark/sql/connect/expressions.py

@@ -809,7 +809,7 @@ def to_plan(self, session: "SparkConnectClient") -> proto.Expression:
         return expr
 
     def __repr__(self) -> str:
-        return f"WithField({self._structExpr}, {self._fieldName}, {self._valueExpr})"
+        return f"update_field({self._structExpr}, {self._fieldName}, {self._valueExpr})"
 
 
 class DropField(Expression):
@@ -833,7 +833,7 @@ def to_plan(self, session: "SparkConnectClient") -> proto.Expression:
         return expr
 
     def __repr__(self) -> str:
-        return f"DropField({self._structExpr}, {self._fieldName})"
+        return f"drop_field({self._structExpr}, {self._fieldName})"
 
 
 class UnresolvedExtractValue(Expression):
@@ -857,7 +857,7 @@ def to_plan(self, session: "SparkConnectClient") -> proto.Expression:
         return expr
 
     def __repr__(self) -> str:
-        return f"UnresolvedExtractValue({str(self._child)}, {str(self._extraction)})"
+        return f"{self._child}['{self._extraction}']"
 
 
 class UnresolvedRegex(Expression):

python/pyspark/sql/tests/test_column.py

@@ -283,6 +283,77 @@ def test_expr_str_representation(self):
         when_cond = sf.when(expression, sf.lit(None))
         self.assertEqual(str(when_cond), "Column<'CASE WHEN foo THEN NULL END'>")
 
+    def test_col_field_ops_representation(self):
+        # SPARK-49894: Test string representation of columns
+        c = sf.col("c")
+
+        # getField
+        self.assertEqual(str(c.x), "Column<'c['x']'>")
+        self.assertEqual(str(c.x.y), "Column<'c['x']['y']'>")
+        self.assertEqual(str(c.x.y.z), "Column<'c['x']['y']['z']'>")
+
+        self.assertEqual(str(c["x"]), "Column<'c['x']'>")
+        self.assertEqual(str(c["x"]["y"]), "Column<'c['x']['y']'>")
+        self.assertEqual(str(c["x"]["y"]["z"]), "Column<'c['x']['y']['z']'>")
+
+        self.assertEqual(str(c.getField("x")), "Column<'c['x']'>")
+        self.assertEqual(
+            str(c.getField("x").getField("y")),
+            "Column<'c['x']['y']'>",
+        )
+        self.assertEqual(
+            str(c.getField("x").getField("y").getField("z")),
+            "Column<'c['x']['y']['z']'>",
+        )
+
+        self.assertEqual(str(c.getItem("x")), "Column<'c['x']'>")
+        self.assertEqual(
+            str(c.getItem("x").getItem("y")),
+            "Column<'c['x']['y']'>",
+        )
+        self.assertEqual(
+            str(c.getItem("x").getItem("y").getItem("z")),
+            "Column<'c['x']['y']['z']'>",
+        )
+
+        self.assertEqual(
+            str(c.x["y"].getItem("z")),
+            "Column<'c['x']['y']['z']'>",
+        )
+        self.assertEqual(
+            str(c["x"].getField("y").getItem("z")),
+            "Column<'c['x']['y']['z']'>",
+        )
+        self.assertEqual(
+            str(c.getField("x").getItem("y").z),
+            "Column<'c['x']['y']['z']'>",
+        )
+        self.assertEqual(
+            str(c["x"].y.getField("z")),
+            "Column<'c['x']['y']['z']'>",
+        )
+
+        # WithField
+        self.assertEqual(
+            str(c.withField("x", sf.col("y"))),
+            "Column<'update_field(c, x, y)'>",
+        )
+        self.assertEqual(
+            str(c.withField("x", sf.col("y")).withField("x", sf.col("z"))),
+            "Column<'update_field(update_field(c, x, y), x, z)'>",
+        )
+
+        # DropFields
+        self.assertEqual(str(c.dropFields("x")), "Column<'drop_field(c, x)'>")
+        self.assertEqual(
+            str(c.dropFields("x", "y")),
+            "Column<'drop_field(drop_field(c, x), y)'>",
+        )
+        self.assertEqual(
+            str(c.dropFields("x", "y", "z")),
+            "Column<'drop_field(drop_field(drop_field(c, x), y), z)'>",
+        )
+
     def test_lit_time_representation(self):
         dt = datetime.date(2021, 3, 4)
         self.assertEqual(str(sf.lit(dt)), "Column<'2021-03-04'>")