def watch(self, tensor):
"""Ensures that `tensor` is being traced by this tape.
Args:
tensor: a Tensor or list of Tensors.
Raises:
ValueError: if it encounters something that is not a tensor.
"""
for t in nest.flatten(tensor):
if not (pywrap_tensorflow.IsTensor(t)
or pywrap_tensorflow.IsVariable(t)):
raise ValueError(
"Passed in object of type {}, not tf.Tensor".format(
type(t)))
if not t.dtype.is_floating:
logging.log_first_n(
logging.WARN, "The dtype of the watched tensor must be "
"floating (e.g. tf.float32), got %r", 5, t.dtype)
if hasattr(t, "handle"):
# There are many variable-like objects, all of them currently have
# `handle` attribute that points to a tensor. If this changes, internals
# of watch_variable need to change as well.
tape.watch_variable(self._tape, t)
else:
tape.watch(self._tape, t)
def constant_value(tensor, partial=False): # pylint: disable=invalid-name
"""Returns the constant value of the given tensor, if efficiently calculable.
This function attempts to partially evaluate the given tensor, and
returns its value as a numpy ndarray if this succeeds.
Compatibility(V1): If `constant_value(tensor)` returns a non-`None` result, it
will no longer be possible to feed a different value for `tensor`. This allows
the result of this function to influence the graph that is constructed, and
permits static shape optimizations.
Args:
tensor: The Tensor to be evaluated.
partial: If True, the returned numpy array is allowed to have partially
evaluated values. Values that can't be evaluated will be None.
Returns:
A numpy ndarray containing the constant value of the given `tensor`,
or None if it cannot be calculated.
Raises:
TypeError: if tensor is not an ops.Tensor.
"""
if isinstance(tensor, ops.EagerTensor):
return tensor.numpy()
if not pywrap_tensorflow.IsTensor(tensor):
return tensor
ret = _ConstantValue(tensor, partial)
if ret is not None:
# The caller may now depend on the constant value of `tensor`, so we
# conservatively prevent it from being fed.
tensor.graph.prevent_feeding(tensor)
return ret