Add stream converter

Convert between numeric and non numeric as well  as sequential and parallel streams

pystreamapi/__stream_converter.py

@@ -0,0 +1,37 @@
+from pystreamapi._streams.__base_stream import BaseStream
+from pystreamapi._streams.__parallel_stream import ParallelStream
+from pystreamapi._streams.__sequential_stream import SequentialStream
+from pystreamapi._streams.numeric.__numeric_base_stream import NumericBaseStream
+from pystreamapi._streams.numeric.__parallel_numeric_stream import ParallelNumericStream
+from pystreamapi._streams.numeric.__sequential_numeric_stream import SequentialNumericStream
+
+
+class StreamConverter:
+    """Class for converting streams to other types of streams."""
+
+    @staticmethod
+    def to_numeric_stream(stream: BaseStream) -> NumericBaseStream:
+        """Converts a stream to a numeric stream."""
+        if isinstance(stream, SequentialStream):
+            stream.__class__ = SequentialNumericStream
+        if isinstance(stream, ParallelStream):
+            stream.__class__ = ParallelNumericStream
+        return stream
+
+    @staticmethod
+    def to_parallel_stream(stream: BaseStream) -> ParallelStream:
+        """Converts a stream to a parallel stream."""
+        if isinstance(stream, SequentialNumericStream):
+            stream.__class__ = ParallelNumericStream
+        elif isinstance(stream, SequentialStream):
+            stream.__class__ = ParallelStream
+        return stream
+
+    @staticmethod
+    def to_sequential_stream(stream: BaseStream) -> SequentialStream:
+        """Converts a stream to a sequential stream."""
+        if isinstance(stream, ParallelNumericStream):
+            stream.__class__ = SequentialNumericStream
+        elif isinstance(stream, ParallelStream):
+            stream.__class__ = SequentialStream
+        return stream

pystreamapi/_streams/__base_stream.py

@@ -16,6 +16,8 @@
 
 if TYPE_CHECKING:
     from pystreamapi._streams.numeric.__numeric_base_stream import NumericBaseStream
+    from pystreamapi._streams.__parallel_stream import ParallelStream
+    from pystreamapi._streams.__sequential_stream import SequentialStream
 
 K = TypeVar('K')
 _V = TypeVar('_V')
@@ -237,6 +239,15 @@ def __map_to_str(self):
         """Converts the stream to strings."""
         self._map(str)
 
+    @_operation
+    def parallel(self) -> 'ParallelStream[K]':
+        """
+        Returns a parallel stream. If the stream is already parallel, it is returned.
+        """
+        # pylint: disable=import-outside-toplevel
+        from pystreamapi.__stream_converter import StreamConverter
+        return StreamConverter.to_parallel_stream(self)
+
     @_operation
     def peek(self, action: Callable) -> 'BaseStream[K]':
         """
@@ -269,6 +280,15 @@ def __reversed(self):
         except TypeError:
             self._source = reversed(list(self._source))
 
+    @_operation
+    def sequential(self) -> SequentialStream[K]:
+        """
+        Returns a sequential stream. If the stream is already sequential, it is returned.
+        """
+        # pylint: disable=import-outside-toplevel
+        from pystreamapi.__stream_converter import StreamConverter
+        return StreamConverter.to_sequential_stream(self)
+
     @_operation
     def skip(self, n: int) -> 'BaseStream[K]':
         """
@@ -430,6 +450,8 @@ def to_dict(self, key_mapper: Callable[[K], Any]) -> dict:
         :param key_mapper:
         """
 
-    @abstractmethod
     def _to_numeric_stream(self) -> NumericBaseStream:
-        """Converts a stream to a numeric stream. To be implemented by subclasses."""
+        """Converts a stream to a numeric stream using the stream converter"""
+        # pylint: disable=import-outside-toplevel
+        from pystreamapi.__stream_converter import StreamConverter
+        return StreamConverter.to_numeric_stream(self)

pystreamapi/_streams/__parallel_stream.py

@@ -91,9 +91,3 @@ def _set_parallelizer_src(self):
 
     def __mapper(self, mapper):
         return lambda x: self._one(mapper=mapper, item=x)
-
-    def _to_numeric_stream(self):
-        # pylint: disable=import-outside-toplevel
-        from pystreamapi._streams.numeric.__parallel_numeric_stream import ParallelNumericStream
-        self.__class__ = ParallelNumericStream
-        return self

pystreamapi/_streams/__sequential_stream.py

@@ -62,9 +62,3 @@ def reduce(self, predicate: Callable, identity=_identity_missing, depends_on_sta
     @stream.terminal
     def to_dict(self, key_mapper: Callable[[Any], Any]) -> dict:
         return self._group_to_dict(key_mapper)
-
-    def _to_numeric_stream(self):
-        # pylint: disable=import-outside-toplevel
-        from pystreamapi._streams.numeric.__sequential_numeric_stream import SequentialNumericStream
-        self.__class__ = SequentialNumericStream
-        return self

tests/test_stream_converter.py

@@ -0,0 +1,54 @@
+from unittest import TestCase
+
+from pystreamapi._streams.__base_stream import BaseStream
+from pystreamapi._streams.__parallel_stream import ParallelStream
+from pystreamapi._streams.__sequential_stream import SequentialStream
+from pystreamapi._streams.numeric.__parallel_numeric_stream import ParallelNumericStream
+from pystreamapi._streams.numeric.__sequential_numeric_stream import SequentialNumericStream
+
+
+class TestStreamConverter(TestCase):
+
+    def test_convert_to_numeric_stream_sequential(self):
+        stream = SequentialStream(["1", "2", "3"]).map_to_int()
+        self.assertIsInstance(stream, SequentialNumericStream)
+
+    def test_convert_to_numeric_stream_parallel(self):
+        stream = ParallelStream(["1", "2", "3"]).map_to_int()
+        self.assertIsInstance(stream, ParallelNumericStream)
+
+    def test_convert_to_numeric_stream_numeric_parallel(self):
+        stream = ParallelNumericStream(["1", "2", "3"]).map_to_int()
+        self.assertIsInstance(stream, ParallelNumericStream)
+
+    def test_convert_to_parallel_stream_sequential(self):
+        stream = SequentialStream(["1", "2", "3"]).parallel()
+        self.assertIsInstance(stream, ParallelStream)
+
+    def test_convert_to_parallel_stream_sequential_numeric(self):
+        stream = SequentialNumericStream(["1", "2", "3"]).parallel()
+        self.assertIsInstance(stream, ParallelNumericStream)
+
+    def test_convert_to_parallel_stream_parallel(self):
+        stream = ParallelStream(["1", "2", "3"]).parallel()
+        self.assertIsInstance(stream, ParallelStream)
+
+    def test_convert_to_parallel_stream_parallel_numeric(self):
+        stream = ParallelNumericStream(["1", "2", "3"]).parallel()
+        self.assertIsInstance(stream, ParallelNumericStream)
+
+    def test_convert_to_sequential_stream_sequential(self):
+        stream = SequentialStream(["1", "2", "3"]).sequential()
+        self.assertIsInstance(stream, SequentialStream)
+
+    def test_convert_to_sequential_stream_sequential_numeric(self):
+        stream = SequentialNumericStream(["1", "2", "3"]).sequential()
+        self.assertIsInstance(stream, SequentialNumericStream)
+
+    def test_convert_to_sequential_stream_parallel(self):
+        stream = ParallelStream(["1", "2", "3"]).sequential()
+        self.assertIsInstance(stream, SequentialStream)
+
+    def test_convert_to_sequential_stream_parallel_numeric(self):
+        stream = ParallelNumericStream(["1", "2", "3"]).sequential()
+        self.assertIsInstance(stream, SequentialNumericStream)