Instantiates a placeholder tensor and returns it. Arguments: shape: Shape of the placeholder (integer tuple, may include `None` entries). ndim: Number of axes of the tensor. At least one of {`shape`, `ndim`} must be specified. If both are specified, `shap
(shape=None,
ndim=None,
dtype=None,
sparse=False,
name=None,
ragged=False)
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