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Compiles a function into a callable TensorFlow graph.
tf.function( func=None, input_signature=None, autograph=True, experimental_implements=None, experimental_autograph_options=None, experimental_relax_shapes=False, experimental_compile=None )
tf.function
constructs a callable that executes a TensorFlow graph (tf.Graph
) created by trace-compiling the TensorFlow operations in func
, effectively executing func
as a TensorFlow graph.
@tf.function def f(x, y): return x ** 2 + y x = tf.constant([2, 3]) y = tf.constant([3, -2]) f(x, y) <tf.Tensor: ... numpy=array([7, 7], ...)>
Features
func
may use data-dependent control flow, including if
, for
, while
break
, continue
and return
statements:
@tf.function def f(x): if tf.reduce_sum(x) > 0: return x * x else: return -x // 2 f(tf.constant(-2)) <tf.Tensor: ... numpy=1>
func
's closure may include tf.Tensor
and tf.Variable
objects:
@tf.function def f(): return x ** 2 + y x = tf.constant([-2, -3]) y = tf.Variable([3, -2]) f() <tf.Tensor: ... numpy=array([7, 7], ...)>
func
may also use ops with side effects, such as tf.print
, tf.Variable
and others:
v = tf.Variable(1) @tf.function def f(x): for i in tf.range(x): v.assign_add(i) f(3) v <tf.Variable ... numpy=4>
l = [] @tf.function def f(x): for i in x: l.append(i + 1) # Caution! Will only happen once when tracing f(tf.constant([1, 2, 3])) l [<tf.Tensor ...>]
Instead, use TensorFlow collections like tf.TensorArray
:
@tf.function def f(x): ta = tf.TensorArray(dtype=tf.int32, size=0, dynamic_size=True) for i in range(len(x)): ta = ta.write(i, x[i] + 1) return ta.stack() f(tf.constant([1, 2, 3])) <tf.Tensor: ..., numpy=array([2, 3, 4], ...)>
tf.function
is polymorphic
Internally, tf.function
can build more than one graph, to support arguments with different data types or shapes, since TensorFlow can build more efficient graphs that are specialized on shapes and dtypes. tf.function
also treats any pure Python value as opaque objects, and builds a separate graph for each set of Python arguments that it encounters.
To obtain an individual graph, use the get_concrete_function
method of the callable created by tf.function
. It can be called with the same arguments as func
and returns a special tf.Graph
object:
@tf.function def f(x): return x + 1 isinstance(f.get_concrete_function(1).graph, tf.Graph) True
@tf.function def f(x): return tf.abs(x) f1 = f.get_concrete_function(1) f2 = f.get_concrete_function(2) # Slow - builds new graph f1 is f2 False f1 = f.get_concrete_function(tf.constant(1)) f2 = f.get_concrete_function(tf.constant(2)) # Fast - reuses f1 f1 is f2 True
Python numerical arguments should only be used when they take few distinct values, such as hyperparameters like the number of layers in a neural network.
Input signatures
For Tensor arguments, tf.function
instantiates a separate graph for every unique set of input shapes and datatypes. The example below creates two separate graphs, each specialized to a different shape:
@tf.function def f(x): return x + 1 vector = tf.constant([1.0, 1.0]) matrix = tf.constant([[3.0]]) f.get_concrete_function(vector) is f.get_concrete_function(matrix) False
An "input signature" can be optionally provided to tf.function
to control the graphs traced. The input signature specifies the shape and type of each Tensor argument to the function using a tf.TensorSpec
object. More general shapes can be used. This is useful to avoid creating multiple graphs when Tensors have dynamic shapes. It also restricts the shape and datatype of Tensors that can be used:
@tf.function( input_signature=[tf.TensorSpec(shape=None, dtype=tf.float32)]) def f(x): return x + 1 vector = tf.constant([1.0, 1.0]) matrix = tf.constant([[3.0]]) f.get_concrete_function(vector) is f.get_concrete_function(matrix) True
Variables may only be created once
tf.function
only allows creating new tf.Variable
objects when it is called for the first time:
class MyModule(tf.Module): def __init__(self): self.v = None @tf.function def __call__(self, x): if self.v is None: self.v = tf.Variable(tf.ones_like(x)) return self.v * x
In general, it is recommended to create stateful objects like tf.Variable
outside of tf.function
and passing them as arguments.
Args | |
---|---|
func | the function to be compiled. If func is None, tf.function returns a decorator that can be invoked with a single argument - func . In other words, tf.function(input_signature=...)(func) is equivalent to tf.function(func, input_signature=...) . The former can be used as decorator. |
input_signature | A possibly nested sequence of tf.TensorSpec objects specifying the shapes and dtypes of the Tensors that will be supplied to this function. If None , a separate function is instantiated for each inferred input signature. If input_signature is specified, every input to func must be a Tensor , and func cannot accept **kwargs . |
autograph | Whether autograph should be applied on func before tracing a graph. Data-dependent control flow requires autograph=True . For more information, see the tf.function and AutoGraph guide. |
experimental_implements | If provided, contains a name of a "known" function this implements. For example "mycompany.my_recurrent_cell". This is stored as an attribute in inference function, which can then be detected when processing serialized function. See standardizing composite ops for details. For an example of utilizing this attribute see this example The code above automatically detects and substitutes function that implements "embedded_matmul" and allows TFLite to substitute its own implementations. For instance, a tensorflow user can use this attribute to mark that their function also implements embedded_matmul (perhaps more efficiently!) by specifying it using this parameter: @tf.function(experimental_implements="embedded_matmul") This can either be specified as just the string name of the function or a NameAttrList corresponding to a list of key-value attributes associated with the function name. The name of the function will be in the 'name' field of the NameAttrList. |
experimental_autograph_options | Optional tuple of tf.autograph.experimental.Feature values. |
experimental_relax_shapes | When True, tf.function may generate fewer, graphs that are less specialized on input shapes. |
experimental_compile | If True, the function is always compiled by XLA. XLA may be more efficient in some cases (e.g. TPU, XLA_GPU, dense tensor computations). |
Returns | |
---|---|
If func is not None, returns a callable that will execute the compiled function (and return zero or more tf.Tensor objects). If func is None, returns a decorator that, when invoked with a single func argument, returns a callable equivalent to the case above. |
Raises | |
---|---|
ValueError when attempting to use experimental_compile, but XLA support is not enabled. |
© 2020 The TensorFlow Authors. All rights reserved.
Licensed under the Creative Commons Attribution License 3.0.
Code samples licensed under the Apache 2.0 License.
https://www.tensorflow.org/versions/r2.3/api_docs/python/tf/function