class_docstr: The base function class.
  To implement a function, write the ``__call__`` method. This takes a
  tensor X and returns a tensor f(X). In accordance with the GPflow
  standard, each row of X represents one datum, and each row of f(X) is computed
  independently for each row of X.
  
  This class is not only used for mean functions.  For example, the variance of a
  heteroskedastic model can be specified using a Function.
  
  :class:`Function` classes can have parameters, see the :class:`Linear` class for an
  example.
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code: def __call__(self, X: TensorType) -> tf.Tensor:
      raise NotImplementedError(
          "Implement the __call__ method for this mean function"
      )
  
imports: from typing import Collection, Optional, Sequence, Tuple
  import numpy
  import tensorflow
  from check_shapes import check_shape
  from check_shapes import check_shapes, inherit_check_shapes
  from .base import Module, Parameter, TensorType
  from .config import default_float, default_int
label_desc: Use image node_id 1 for calling the Function obj's underlying member method code with example usage: obj.__call__(X) without return types