[PYTHON] Fix typo in serializer exception

## What changes were proposed in this pull request?

Fix typo in exception raised in Python serializer

## How was this patch tested?

No code changes

Please review http://spark.apache.org/contributing.html before opening a pull request.

Author: Ruben Berenguel Montoro <ruben@mostlymaths.net>

Closes #21566 from rberenguel/fix_typo_pyspark_serializers.

Author: rberenguel

python/pyspark/serializers.py

@@ -33,8 +33,9 @@
 [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
 >>> sc.stop()
 
-PySpark serialize objects in batches; By default, the batch size is chosen based
-on the size of objects, also configurable by SparkContext's C{batchSize} parameter:
+PySpark serializes objects in batches; by default, the batch size is chosen based
+on the size of objects and is also configurable by SparkContext's C{batchSize}
+parameter:
 
 >>> sc = SparkContext('local', 'test', batchSize=2)
 >>> rdd = sc.parallelize(range(16), 4).map(lambda x: x)
@@ -100,7 +101,7 @@ def load_stream(self, stream):
     def _load_stream_without_unbatching(self, stream):
         """
         Return an iterator of deserialized batches (iterable) of objects from the input stream.
-        if the serializer does not operate on batches the default implementation returns an
+        If the serializer does not operate on batches the default implementation returns an
         iterator of single element lists.
         """
         return map(lambda x: [x], self.load_stream(stream))
@@ -461,7 +462,7 @@ def dumps(self, obj):
         return obj
 
 
-# Hook namedtuple, make it picklable
+# Hack namedtuple, make it picklable
 
 __cls = {}
 
@@ -525,15 +526,15 @@ def namedtuple(*args, **kwargs):
         cls = _old_namedtuple(*args, **kwargs)
         return _hack_namedtuple(cls)
 
-    # replace namedtuple with new one
+    # replace namedtuple with the new one
     collections.namedtuple.__globals__["_old_namedtuple_kwdefaults"] = _old_namedtuple_kwdefaults
     collections.namedtuple.__globals__["_old_namedtuple"] = _old_namedtuple
     collections.namedtuple.__globals__["_hack_namedtuple"] = _hack_namedtuple
     collections.namedtuple.__code__ = namedtuple.__code__
     collections.namedtuple.__hijack = 1
 
-    # hack the cls already generated by namedtuple
-    # those created in other module can be pickled as normal,
+    # hack the cls already generated by namedtuple.
+    # Those created in other modules can be pickled as normal,
     # so only hack those in __main__ module
     for n, o in sys.modules["__main__"].__dict__.items():
         if (type(o) is type and o.__base__ is tuple
@@ -627,7 +628,7 @@ def loads(self, obj):
         elif _type == b'P':
             return pickle.loads(obj[1:])
         else:
-            raise ValueError("invalid sevialization type: %s" % _type)
+            raise ValueError("invalid serialization type: %s" % _type)
 
 
 class CompressedSerializer(FramedSerializer):