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fchollet's profile
François Chollet
François Chollet
François Chollet
Verified account
@fchollet

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François CholletVerified account

@fchollet

Deep learning @google. Creator of Keras. Author of 'Deep Learning with Python'. Opinions are my own.

United States
fchollet.com
Joined August 2009

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    1. François Chollet‏Verified account @fchollet Jul 12

      Tweetorial: the Functional API in Keras. Deep learning models are basically graphs of layers. Therefore, an intuitive API for defining deep learning models should be a *graph-definition API*. That's what the Functional API is: a Python-based DSL for graphs. It looks like this:pic.twitter.com/rthCY2Jqhz

      5 replies 102 retweets 577 likes
      Show this thread
    2. François Chollet‏Verified account @fchollet Jul 12

      This builds the following graph:pic.twitter.com/WQzvf6bJZh

      1 reply 1 retweet 24 likes
      Show this thread
    3. François Chollet‏Verified account @fchollet Jul 12

      Now, of course, you could also define such a model as a Python class. It would then look like this:pic.twitter.com/2oU0vjOIHe

      3 replies 1 retweet 26 likes
      Show this thread
    4. François Chollet‏Verified account @fchollet Jul 12

      But there are several key advantages of the Functional approach over the subclassing approach: 1. Your model has known inputs shapes. 2. You get access to the internal connectivity graph. 3. The model is a data structure, not a piece of bytecode. Let's see what these are about.

      2 replies 0 retweets 33 likes
      Show this thread
    5. François Chollet‏Verified account @fchollet Jul 12

      1. Because the model has known input shapes, it's capable of running input validation checks, for easy debugging:pic.twitter.com/1B8E7GXmK1

      1 reply 1 retweet 19 likes
      Show this thread
    6. François Chollet‏Verified account @fchollet Jul 12

      Further, it's even capable of standardizing inputs to what it expects: if you pass data of shape (batch_size,) to a model that expects (batch_size, 1), it will just reshape it. Likewise for dtype conversion (e.g. float64 will get converted to float32).

      1 reply 0 retweets 15 likes
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    7. François Chollet‏Verified account @fchollet Jul 12

      2. You get access to the internal connectivity graph. This means you can plot the model, for instance. This is great for debugging. Like this:pic.twitter.com/ZnG6ym9yei

      1 reply 0 retweets 38 likes
      Show this thread
    8. François Chollet‏Verified account @fchollet Jul 12

      Having access to internal nodes also means you can access an intermediate layer output and leverage it in a new model. This is a killer feature for feature extraction, fine-tuning, and ensembling. Let's add an extra output to the model above:pic.twitter.com/gCxafm21UF

      1 reply 0 retweets 27 likes
      Show this thread
      François Chollet‏Verified account @fchollet Jul 12

      3. The model is a data structure, not a piece of bytecode. This means it can be cleanly serialized and deserialized -- even across platforms. keras.Model.from_config(functional_model.get_config()) reconstructs the exact same model as the original.

      12:35 PM - 12 Jul 2021
      • 1 Retweet
      • 24 Likes
      • House of Black&White MaXuLtRa HajEsmal Mario Krous Luciano Lorenti 🎱🦑 Antonio Lozano Juan Pedro Fisanotti Akash Jain
      1 reply 1 retweet 24 likes
        1. New conversation
        2. François Chollet‏Verified account @fchollet Jul 12

          If your model is a Python subclass, to serialize it you could either: a. Pickle the bytecode -- which it completely unsafe, won't work for production, and won't work across platforms

          2 replies 2 retweets 15 likes
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        3. François Chollet‏Verified account @fchollet Jul 12

          b. Save it as a SavedModel -- which is a form of one-way export (of the TF graph) and won't let you reconstruct the exact same Python object. A graph of layers is a data structure; defining and saving it as a data structure is the intuitive thing to do.

          2 replies 3 retweets 20 likes
          Show this thread
        4. François Chollet‏Verified account @fchollet Jul 12

          Many runtimes other than Python TensorFlow understand the Keras graph-of-layers format, such as TF.js, CoreML, DeepLearning4J... A high level, human-readable saving format is much easier to implement for third-party platforms.

          1 reply 2 retweets 21 likes
          Show this thread
        5. François Chollet‏Verified account @fchollet Jul 12

          A last advantage of the Functional API I haven't listed here is that it is much less verbose, because it is less redundant (no need to list/name each layer twice). Consider this subclassed VAE vs. an equivalent Functional model...pic.twitter.com/hkxVE8eXlZ

          1 reply 2 retweets 35 likes
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        6. François Chollet‏Verified account @fchollet Jul 12

          Note that you don't have to inline your Functional model definitions all the time -- complex models should be broken down into stateless functions (one function per architectural block). Here's an example of a Transformer for timeseries classification.pic.twitter.com/gBi4mO2FyT

          2 replies 3 retweets 63 likes
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        7. François Chollet‏Verified account @fchollet Jul 12

          That's it for this tweetorial. Feel free to chime in with your own takes on pros and cons of the Functional and subclassing approaches!

          9 replies 3 retweets 40 likes
          Show this thread
        8. End of conversation

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