Adapted Data Contexts

Often the data inside a context needs to be transformed in some way before it is used:

• possibly in different ways by different parts on an application
• with different transformations on different variables
• with multiple different transformations applied sequentially

And the same sequence of transformations may need to be reversed when setting a value in to the context. These transformations may even need to be changed depending on the situation or a user request.

The AdaptedDataContext class provides a framework for applying transformations to data as it comes in and out of a context. AdaptedDataContext provides a list of adapters in its adapters trait attribute, as well as push() and pop() methods for manipulating them. On get, set, or delete operations, the AdapterManagerMixin goes through each of the adapters and first calls the adapt_name() method to perform any manipulations of the name, and then calls adapt_getitem() or adapt_setitem() for get and set operations respectively. Once all the adapters have had a chance to perform transformations, the operation is applied to the underlying context.

To create an adapter all you need to do is to implement the IAdapter interface by providing at least one of the adapt_name(), adapt_getitem(), or adapt_setitem() methods.

from numpy import ndarray
from numpy.fft import fft, ifft
from traits.api import HasTraits, provides
from codetools.contexts.api import IAdapter

@provides(IAdapter)
class FFTAdapter(HasTraits):

    def adapt_getitem(self, context, key, value):
        """Take Fourier transform of 1-D Numpy arrays in the context."""
        if isinstance(value, ndarray) and len(value.shape) == 1:
            return key, fft(value)

    def adapt_setitem(self, context, key, value):
        """Take inverse Fourier transform of 1D numpy arrays when setting into
        the context."""
        if isinstance(value, ndarray) and len(value.shape) == 1:
            return key, ifft(value)

The codetools.contexts package contains a number of adapters to perform operations like masking, unit conversion, and name translation.