Function _slice_helper

tensorflow/python/ops/array_ops.py:658–802

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 exampl

(tensor, slice_spec, var=None)

def _slice_helper(tensor, slice_spec, var=None):
  """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:

  ```python
  # 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].eval())  # => [[3,2,1], [9,8,7]]

  # Use scalar tensors as indices on both dimensions
  print(foo[tf.constant(0), tf.constant(2)].eval())  # => 3

  # Insert another dimension
  foo = tf.constant([[1,2,3], [4,5,6], [7,8,9]])
  print(foo[tf.newaxis, :, :].eval()) # => [[[1,2,3], [4,5,6], [7,8,9]]]
  print(foo[:, tf.newaxis, :].eval()) # => [[[1,2,3]], [[4,5,6]], [[7,8,9]]]
  print(foo[:, :, tf.newaxis].eval()) # => [[[1],[2],[3]], [[4],[5],[6]],
  [[7],[8],[9]]]

  # Ellipses (3 equivalent operations)
  foo = tf.constant([[1,2,3], [4,5,6], [7,8,9]])
  print(foo[tf.newaxis, :, :].eval())  # => [[[1,2,3], [4,5,6], [7,8,9]]]
  print(foo[tf.newaxis, ...].eval())  # => [[[1,2,3], [4,5,6], [7,8,9]]]
  print(foo[tf.newaxis].eval())  # => [[[1,2,3], [4,5,6], [7,8,9]]]

  # Masks
  foo = tf.constant([[1,2,3], [4,5,6], [7,8,9]])
  print(foo[foo > 2].eval())  # => [3, 4, 5, 6, 7, 8, 9]
  ```

  Notes:
    - `tf.newaxis` is `None` as in NumPy.
    - An implicit ellipsis is placed at the end of the `slice_spec`
    - NumPy advanced indexing is currently not supported.

  Args:
    tensor: An ops.Tensor object.
    slice_spec: The arguments to Tensor.__getitem__.
    var: In the case of variable slice assignment, the Variable object to slice
      (i.e. tensor is the read-only view of this variable).

  Returns:
    The appropriate slice of "tensor", based on "slice_spec".

  Raises:
    ValueError: If a slice range is negative size.
    TypeError: If the slice indices aren't int, slice, ellipsis,
      tf.newaxis or scalar int32/int64 tensors.