TensorFlow is designed as a framework that supports both production and research code. After using TensorFlow for several years and being involved in its development, I collected a few patterns for faster prototyping that I found myself using in many research projects. This post also introduces an alternative to my previous post on structuring models.

Dictionary with less typing

Rapid prototyping requires flexible data structures, such as dictionaries. However, in Python that means typing a lot of square brackets and quotes. The following trick defines an attribute dictionary that allows us to address keys as if they were attributes:

class AttrDict(dict):
  __getattr__ = dict.__getitem__
  __setattr__ = dict.__setitem__

Since the class inherits from dict, we can still use the object everywhere where we can use a dictionary. The attribute dictionary is useful for example to define experiment configurations:

def define_config():
  config = AttrDict()
  config.layer_sizes = [100, 100]
  config.output_size = 10
  config.learning_rate = 1e-3
  return config

config = define_config()
print(config.learning_rate)

A more sophisticated version of the attribute dictionary could add a method to freeze its object to prevent accidental changes. If you want more flexibility than that, check out Ian Fischer’s pstar library.

Decorator to share variables

Many neural network models reuse parts of the network, for example to apply them to different inputs or to share weights. TensorFlow’s tf.make_template() wraps a function to ensure that all its invokations use the same weights (or raise an error). However, it is a bit clumsy to use, so the following decorator makes it easier:

share_variables = lambda func: tf.make_template(
    func.__name__, func, create_scope_now_=True)

This allows us to decorate functions to share the variables between all calls of the function. Just place the @share_variables decorator before the function name:

@share_variables
def my_network(inputs, config):
  hidden = tf.layers.flatten(inputs)
  for size in config.layer_sizes:
    hidden = tf.layers.dense(hidden, size, tf.nn.relu)
  prediction = tf.layers.dense(hidden, config.output_size)
  return prediction

An extended version of this decorator also supports methods of classes, so that each object uses its own weights, but method calls on the same object share weights. I have created a code example of this template decorator.

Hold the graph together

A typical problem when writing TensorFlow code is that many quantities exist both as tensors in the graph and as actual values. To avoid confusion among all the objects, it is useful to group the tensors together into a graph object. This also allows to quickly pass the whole graph to a function.

def define_graph(config):
  tf.reset_default_graph()
  inputs, targets = define_data_pipeline()
  prediction = my_network(inputs, config)
  loss = tf.losses.mean_squared_error(targets, prediction)
  optimizer = config.optimizer()
  optimize = optimizer.minimize(loss)
  return AttrDict(locals())  # The magic line.

The above function defines a lot of tensors for our model. It then uses locals() to access the dictionary of all local variables, and wraps them into an attribute dictionary that we defined earlier. As a result, we can access tensors via the graph object:

graph = define_graph(config)
with tf.Session() as sess:
  sess.run(tf.global_variables_initializer())
  for _ in range(config.num_epochs):
    sess.run(graph.optimize)
  loss = sess.run(graph.loss)  # No name collision anymore.
  print(loss)

Conclusion

I hope these ideas help you to be more productive at prototyping with TensorFlow. Some of the ideas are certainly not well suited for production code. But they allow you to iterate quickly – one of the most important aspects of research. Please feel free to share your thoughts and feedback.

You can use this post under the open CC BY-SA 3.0 license and cite it as:

@misc{hafner2018tfprototyping,
  author = {Hafner, Danijar},
  title = {Patterns for Fast Prototyping with TensorFlow},
  year = {2018},
  howpublished = {Blog post},
  url = {https://danijar.com/patterns-for-fast-prototyping-with-tensorflow/}
}