Add stacked processors

bob/extension/processors.py

+class SequentialProcessor(object):
+    """A helper class which takes several processors and applies them one by
+    one on data sequentially. See :ref:`bob.extension.processors` for more
+    details.
+
+    Attributes
+    ----------
+    processors : list
+        A list of processors to apply.
+    """
+
+    def __init__(self, processors, **kwargs):
+        """Initialization
+
+        Parameters
+        ----------
+        processors : :py:class:`list`
+            A list of preprocessors to be used.
+        **kwargs
+            Any kwargs are passed to the parent class.
+        """
+        super(SequentialProcessor, self).__init__(**kwargs)
+        self.processors = processors
+
+    def __call__(self, data, **kwargs):
+        """Applies the processors on the data sequentially. The output of the
+        first one goes as input to the next one.
+
+        Parameters
+        ----------
+        data : object
+            The data that needs to be processed.
+        **kwargs
+            Any kwargs are passed to the processors.
+
+        Returns
+        -------
+        object
+            The processed data.
+        """
+        for processor in self.processors:
+            data = processor(data, **kwargs)
+        return data
+
+
+class ParallelProcessor(object):
+    """A helper class which takes several processors and applies data on each
+    processor separately and yields their outputs one by one. See
+    :ref:`bob.extension.processors` for more details.
+
+    Attributes
+    ----------
+    processors : list
+        A list of processors to apply.
+    """
+
+    def __init__(self, processors, **kwargs):
+        """Initialization
+
+        Parameters
+        ----------
+        processors : :py:class:`list`
+            A list of preprocessors to be used.
+        **kwargs
+            Any kwargs are passed to the parent class.
+        """
+        super(ParallelProcessor, self).__init__(**kwargs)
+        self.processors = processors
+
+    def __call__(self, data, **kwargs):
+        """Applies the processors on the data independently and outputs a
+        generator of their outputs.
+
+        Parameters
+        ----------
+        data : object
+            The data that needs to be processed.
+        **kwargs
+            Any kwargs are passed to the processors.
+
+        Yields
+        ------
+        object
+            The processed data from processors one by one.
+        """
+        for processor in self.processors:
+            yield processor(data, **kwargs)