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tf.Tensor

TensorFlow 2 version View source on GitHub

Represents one of the outputs of an Operation.

A Tensor is a symbolic handle to one of the outputs of an Operation. It does not hold the values of that operation's output, but instead provides a means of computing those values in a TensorFlow tf.compat.v1.Session.

This class has two primary purposes:

  1. A Tensor can be passed as an input to another Operation. This builds a dataflow connection between operations, which enables TensorFlow to execute an entire Graph that represents a large, multi-step computation.

  2. After the graph has been launched in a session, the value of the Tensor can be computed by passing it to tf.Session.run. t.eval() is a shortcut for calling tf.compat.v1.get_default_session().run(t).

In the following example, c, d, and e are symbolic Tensor objects, whereas result is a numpy array that stores a concrete value:

# Build a dataflow graph.
c = tf.constant([[1.0, 2.0], [3.0, 4.0]])
d = tf.constant([[1.0, 1.0], [0.0, 1.0]])
e = tf.matmul(c, d)

# Construct a `Session` to execute the graph.
sess = tf.compat.v1.Session()

# Execute the graph and store the value that `e` represents in `result`.
result = sess.run(e)

op An Operation. Operation that computes this tensor.
value_index An int. Index of the operation's endpoint that produces this tensor.
dtype A DType. Type of elements stored in this tensor.

TypeError If the op is not an Operation.

device The name of the device on which this tensor will be produced, or None.
dtype The DType of elements in this tensor.
graph The Graph that contains this tensor.
name The string name of this tensor.
op The Operation that produces this tensor as an output.
shape Returns the TensorShape that represents the shape of this tensor.

The shape is computed using shape inference functions that are registered in the Op for each Operation. See tf.TensorShape for more details of what a shape represents.

The inferred shape of a tensor is used to provide shape information without having to launch the graph in a session. This can be used for debugging, and providing early error messages. For example:

c = tf.constant([[1.0, 2.0, 3.0], [4.0, 5.0, 6.0]])

print(c.shape)
==> TensorShape([Dimension(2), Dimension(3)])

d = tf.constant([[1.0, 0.0], [0.0, 1.0], [1.0, 0.0], [0.0, 1.0]])

print(d.shape)
==> TensorShape([Dimension(4), Dimension(2)])

# Raises a ValueError, because `c` and `d` do not have compatible
# inner dimensions.
e = tf.matmul(c, d)

f = tf.matmul(c, d, transpose_a=True, transpose_b=True)

print(f.shape)
==> TensorShape([Dimension(3), Dimension(4)])

In some cases, the inferred shape may have unknown dimensions. If the caller has additional information about the values of these dimensions, Tensor.set_shape() can be used to augment the inferred shape.

value_index The index of this tensor in the outputs of its Operation.

Methods

consumers

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Returns a list of Operations that consume this tensor.

Returns
A list of Operations.

eval

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Evaluates this tensor in a Session.

Calling this method will execute all preceding operations that produce the inputs needed for the operation that produces this tensor.

Args
feed_dict A dictionary that maps Tensor objects to feed values. See tf.Session.run for a description of the valid feed values.
session (Optional.) The Session to be used to evaluate this tensor. If none, the default session will be used.

Returns
A numpy array corresponding to the value of this tensor.

experimental_ref

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Returns a hashable reference object to this Tensor.

The primary usecase for this API is to put tensors in a set/dictionary. We can't put tensors in a set/dictionary as tensor.__hash__() is no longer available starting Tensorflow 2.0.

import tensorflow as tf

x = tf.constant(5)
y = tf.constant(10)
z = tf.constant(10)

# The followings will raise an exception starting 2.0
# TypeError: Tensor is unhashable if Tensor equality is enabled.
tensor_set = {x, y, z}
tensor_dict = {x: 'five', y: 'ten', z: 'ten'}

Instead, we can use tensor.experimental_ref().

tensor_set = {x.experimental_ref(),
              y.experimental_ref(),
              z.experimental_ref()}

print(x.experimental_ref() in tensor_set)
==> True

tensor_dict = {x.experimental_ref(): 'five',
               y.experimental_ref(): 'ten',
               z.experimental_ref(): 'ten'}

print(tensor_dict[y.experimental_ref()])
==> ten

Also, the reference object provides .deref() function that returns the original Tensor.

x = tf.constant(5)
print(x.experimental_ref().deref())
==> tf.Tensor(5, shape=(), dtype=int32)

get_shape

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Alias of Tensor.shape.

set_shape

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Updates the shape of this tensor.

This method can be called multiple times, and will merge the given shape with the current shape of this tensor. It can be used to provide additional information about the shape of this tensor that cannot be inferred from the graph alone. For example, this can be used to provide additional information about the shapes of images:

_, image_data = tf.compat.v1.TFRecordReader(...).read(...)
image = tf.image.decode_png(image_data, channels=3)

# The height and width dimensions of `image` are data dependent, and
# cannot be computed without executing the op.
print(image.shape)
==> TensorShape([Dimension(None), Dimension(None), Dimension(3)])

# We know that each image in this dataset is 28 x 28 pixels.
image.set_shape([28, 28, 3])
print(image.shape)
==> TensorShape([Dimension(28), Dimension(28), Dimension(3)])

Args
shape A TensorShape representing the shape of this tensor, a TensorShapeProto, a list, a tuple, or None.

Raises
ValueError If shape is not compatible with the current shape of this tensor.

__abs__

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Computes the absolute value of a tensor.

Given a tensor of integer or floating-point values, this operation returns a tensor of the same type, where each element contains the absolute value of the corresponding element in the input.

Given a tensor x of complex numbers, this operation returns a tensor of type float32 or float64 that is the absolute value of each element in x. All elements in x must be complex numbers of the form \(a + bj\). The absolute value is computed as \( \sqrt{a^2 + b^2}\). For example:

x = tf.constant([[-2.25 + 4.75j], [-3.25 + 5.75j]])
tf.abs(x)  # [5.25594902, 6.60492229]

Args
x A Tensor or SparseTensor of type float16, float32, float64, int32, int64, complex64 or complex128.
name A name for the operation (optional).

Returns
A Tensor or SparseTensor the same size, type, and sparsity as x with absolute values. Note, for complex64 or complex128 input, the returned Tensor will be of type float32 or float64, respectively.

If x is a SparseTensor, returns SparseTensor(x.indices, tf.math.abs(x.values, ...), x.dense_shape)

__add__

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Dispatches to add for strings and add_v2 for all other types.

__and__

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Returns the truth value of x AND y element-wise.

Args
x A Tensor of type bool.
y A Tensor of type bool.
name A name for the operation (optional).

Returns
A Tensor of type bool.

__bool__

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Dummy method to prevent a tensor from being used as a Python bool.

This overload raises a TypeError when the user inadvertently treats a Tensor as a boolean (most commonly in an if or while statement), in code that was not converted by AutoGraph. For example:

if tf.constant(True):  # Will raise.
  # ...

if tf.constant(5) < tf.constant(7):  # Will raise.
  # ...

Raises
TypeError.

__div__

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Divide two values using Python 2 semantics.

Used for Tensor.div.

Args
x Tensor numerator of real numeric type.
y Tensor denominator of real numeric type.
name A name for the operation (optional).

Returns
x / y returns the quotient of x and y.

__eq__

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Compares two tensors element-wise for equality.

__floordiv__

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Divides x / y elementwise, rounding toward the most negative integer.

The same as tf.compat.v1.div(x,y) for integers, but uses tf.floor(tf.compat.v1.div(x,y)) for floating point arguments so that the result is always an integer (though possibly an integer represented as floating point). This op is generated by x // y floor division in Python 3 and in Python 2.7 with from __future__ import division.

x and y must have the same type, and the result will have the same type as well.

Args
x Tensor numerator of real numeric type.
y Tensor denominator of real numeric type.
name A name for the operation (optional).

Returns
x / y rounded down.

Raises
TypeError If the inputs are complex.

__ge__

Returns the truth value of (x >= y) element-wise.

Args
x A Tensor. Must be one of the following types: float32, float64, int32, uint8, int16, int8, int64, bfloat16, uint16, half, uint32, uint64.
y A Tensor. Must have the same type as x.
name A name for the operation (optional).

Returns
A Tensor of type bool.

__getitem__

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Overload for Tensor.getitem.

This operation extracts the specified region from the tensor. The notation is similar to NumPy with the restriction that currently only support basic indexing. That means that using a non-scalar tensor as input is not currently allowed.

Some useful examples:

# Strip leading and trailing 2 elements
foo = tf.constant([1,2,3,4,5,6])
print(foo[2:-2].eval())  # => [3,4]

# Skip every other row and reverse the order of the columns
foo = tf.constant([[1,2,3], [4,5,6], [7,8,9]])
print(foo[::2,::-1]