A multiplexing Thumbor engine that prefers OpenCV where possible, and falls back to Pillow for unsupported image types.

engine.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

# Licensed under the MIT license:
# http://www.opensource.org/licenses/mit-license
# Copyright (c) 2013 arthens@gmail.com

import magic
from thumbor.engines import pil, opencv

class Engine:

    def __init__(self, context):
        self.opencv = opencv.Engine(context)
        self.pil = pil.Engine(context)
        self.activeEngine = None

    def __getattr__(self, item):
        return getattr(self.activeEngine, item)

    def load(self, buffer, extension):
        if self._use_opencv(buffer):
            self.opencv.load(buffer, extension)
            self.activeEngine = self.opencv
        else:
            self.pil.load(buffer, extension)
            self.activeEngine = self.pil

    def _use_opencv(self, buffer):
        """
        Determine if buffer can be resized using OpenCV. OpenCV can't handle
        GIFs, or PNGs with alpha transparency, but is much faster than the other
        engine implementations.
        """
        file_description = self._describe_contents(buffer)
        return 'GIF' not in file_description and 'RGBA' not in file_description

    def _describe_contents(self, buffer):
        """
        Use libmagic to get a string describing the contents of buffer.
        """

        # There are two Python libraries that wrap libmagic: python-magic[1] and
        # magic-python[2]. Both define the module `magic`. Thumbor already uses
        # python-magic, but due to a packaging issue[3] magic-python is included
        # when Thumbor is installed as a package (e.g. via apt-get).
        #
        # Due to this unfortunate series of events, we can't predict which
        # library is available ahead of time. Instead we have to detect at
        # runtime and respond accordingly.
        #
        #  [1]: https://github.com/ahupp/python-magic
        #  [2]: https://github.com/mammadori/magic-python
        #  [3]: https://github.com/globocom/thumbor/issues/188

        try:
            # python-magic
            return magic.from_buffer(buffer)
        except AttributeError:
            # magic-python
            m = magic.open(magic.NONE)
            m.load()
            result = m.buffer(buffer)
            m.close()
            return result