STT-tensorflow/tensorflow/lite/g3doc/r1/convert/python_api.md

Converter Python API guide

This page describes how to convert TensorFlow models into the TensorFlow Lite format using the TensorFlow Lite Converter Python API.

If you're looking for information about how to run a TensorFlow Lite model, see TensorFlow Lite inference.

Note: This page describes the converter in the TensorFlow nightly release, installed using pip install tf-nightly. For docs describing older versions reference "Converting models from TensorFlow 1.12".

High-level overview

While the TensorFlow Lite Converter can be used from the command line, it is often convenient to use in a Python script as part of the model development pipeline. This allows you to know early that you are designing a model that can be targeted to devices with mobile.

API

The API for converting TensorFlow models to TensorFlow Lite is tf.lite.TFLiteConverter, which provides class methods based on the original format of the model. For example, TFLiteConverter.from_session() is available for GraphDefs, TFLiteConverter.from_saved_model() is available for SavedModels, and TFLiteConverter.from_keras_model_file() is available for tf.Keras files.

Example usages for simple float-point models are shown in Basic Examples. Examples usages for more complex models is shown in Complex Examples.

Basic examples

The following section shows examples of how to convert a basic float-point model from each of the supported data formats into a TensorFlow Lite FlatBuffers.

Exporting a GraphDef from tf.Session

The following example shows how to convert a TensorFlow GraphDef into a TensorFlow Lite FlatBuffer from a tf.Session object.

import tensorflow as tf

img = tf.placeholder(name="img", dtype=tf.float32, shape=(1, 64, 64, 3))
var = tf.get_variable("weights", dtype=tf.float32, shape=(1, 64, 64, 3))
val = img + var
out = tf.identity(val, name="out")

with tf.Session() as sess:
  sess.run(tf.global_variables_initializer())
  converter = tf.lite.TFLiteConverter.from_session(sess, [img], [out])
  tflite_model = converter.convert()
  open("converted_model.tflite", "wb").write(tflite_model)

Exporting a GraphDef from file

The following example shows how to convert a TensorFlow GraphDef into a TensorFlow Lite FlatBuffer when the GraphDef is stored in a file. Both .pb and .pbtxt files are accepted.

The example uses Mobilenet_1.0_224. The function only supports GraphDefs frozen using freeze_graph.py.

import tensorflow as tf

graph_def_file = "/path/to/Downloads/mobilenet_v1_1.0_224/frozen_graph.pb"
input_arrays = ["input"]
output_arrays = ["MobilenetV1/Predictions/Softmax"]

converter = tf.lite.TFLiteConverter.from_frozen_graph(
  graph_def_file, input_arrays, output_arrays)
tflite_model = converter.convert()
open("converted_model.tflite", "wb").write(tflite_model)

Exporting a SavedModel

The following example shows how to convert a SavedModel into a TensorFlow Lite FlatBuffer.

import tensorflow as tf

converter = tf.lite.TFLiteConverter.from_saved_model(saved_model_dir)
tflite_model = converter.convert()
open("converted_model.tflite", "wb").write(tflite_model)

For more complex SavedModels, the optional parameters that can be passed into TFLiteConverter.from_saved_model() are input_arrays, input_shapes, output_arrays, tag_set and signature_key. Details of each parameter are available by running help(tf.lite.TFLiteConverter).

Exporting a tf.keras File

The following example shows how to convert a tf.keras model into a TensorFlow Lite FlatBuffer. This example requires h5py to be installed.

import tensorflow as tf

converter = tf.lite.TFLiteConverter.from_keras_model_file("keras_model.h5")
tflite_model = converter.convert()
open("converted_model.tflite", "wb").write(tflite_model)

The tf.keras file must contain both the model and the weights. A comprehensive example including model construction can be seen below.

import numpy as np
import tensorflow as tf

# Generate tf.keras model.
model = tf.keras.models.Sequential()
model.add(tf.keras.layers.Dense(2, input_shape=(3,)))
model.add(tf.keras.layers.RepeatVector(3))
model.add(tf.keras.layers.TimeDistributed(tf.keras.layers.Dense(3)))
model.compile(loss=tf.keras.losses.MSE,
              optimizer=tf.keras.optimizers.RMSprop(lr=0.0001),
              metrics=[tf.keras.metrics.categorical_accuracy],
              sample_weight_mode='temporal')

x = np.random.random((1, 3))
y = np.random.random((1, 3, 3))
model.train_on_batch(x, y)
model.predict(x)

# Save tf.keras model in HDF5 format.
keras_file = "keras_model.h5"
tf.keras.models.save_model(model, keras_file)

# Convert to TensorFlow Lite model.
converter = tf.lite.TFLiteConverter.from_keras_model_file(keras_file)
tflite_model = converter.convert()
open("converted_model.tflite", "wb").write(tflite_model)

Complex examples

For models where the default value of the attributes is not sufficient, the attribute's values should be set before calling convert(). In order to call any constants use tf.lite.constants.<CONSTANT_NAME> as seen below with QUANTIZED_UINT8. Run help(tf.lite.TFLiteConverter) in the Python terminal for detailed documentation on the attributes.

Although the examples are demonstrated on GraphDefs containing only constants. The same logic can be applied irrespective of the input data format.

Exporting a quantized GraphDef

The following example shows how to convert a quantized model into a TensorFlow Lite FlatBuffer.

import tensorflow as tf

img = tf.placeholder(name="img", dtype=tf.float32, shape=(1, 64, 64, 3))
const = tf.constant([1., 2., 3.]) + tf.constant([1., 4., 4.])
val = img + const
out = tf.fake_quant_with_min_max_args(val, min=0., max=1., name="output")

with tf.Session() as sess:
  converter = tf.lite.TFLiteConverter.from_session(sess, [img], [out])
  converter.inference_type = tf.lite.constants.QUANTIZED_UINT8
  input_arrays = converter.get_input_arrays()
  converter.quantized_input_stats = {input_arrays[0] : (0., 1.)}  # mean, std_dev
  tflite_model = converter.convert()
  open("converted_model.tflite", "wb").write(tflite_model)

Additional instructions

Build from source code

In order to run the latest version of the TensorFlow Lite Converter Python API, either install the nightly build with pip (recommended) or Docker, or build the pip package from source.

Converting models from TensorFlow 1.12

Reference the following table to convert TensorFlow models to TensorFlow Lite in and before TensorFlow 1.12. Run help() to get details of each API.

TensorFlow Version	Python API
1.12	tf.contrib.lite.TFLiteConverter
1.9-1.11	tf.contrib.lite.TocoConverter
1.7-1.8	tf.contrib.lite.toco_convert