[SPARK-7544] [SQL] [PySpark] pyspark.sql.types.Row implements __getitem__

pyspark.sql.types.Row implements ```__getitem__```

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #8333 from yanboliang/spark-7544.

python/pyspark/sql/types.py

@@ -1176,6 +1176,8 @@ class Row(tuple):
     >>> row = Row(name="Alice", age=11)
     >>> row
     Row(age=11, name='Alice')
+    >>> row['name'], row['age']
+    ('Alice', 11)
     >>> row.name, row.age
     ('Alice', 11)
 
@@ -1243,6 +1245,19 @@ class Row(tuple):
         """create new Row object"""
         return _create_row(self, args)
 
+    def __getitem__(self, item):
+        if isinstance(item, (int, slice)):
+            return super(Row, self).__getitem__(item)
+        try:
+            # it will be slow when it has many fields,
+            # but this will not be used in normal cases
+            idx = self.__fields__.index(item)
+            return super(Row, self).__getitem__(idx)
+        except IndexError:
+            raise KeyError(item)
+        except ValueError:
+            raise ValueError(item)
+
     def __getattr__(self, item):
         if item.startswith("__"):
             raise AttributeError(item)