[core API doc fixit] tf.get_static_value; updated the API doc with more explanations and examples.

PiperOrigin-RevId: 348495511
Change-Id: I28b6c2c4822fd2d62eabbb535282ac5087765fae

tensorflow/python/framework/tensor_util.py

@@ -809,6 +809,41 @@ def constant_value(tensor, partial=False):  # pylint: disable=invalid-name
   This function attempts to partially evaluate the given tensor, and
   returns its value as a numpy ndarray if this succeeds.
 
+  Example usage:
+
+  >>> a = tf.constant(10)
+  >>> tf.get_static_value(a)
+  10
+  >>> b = tf.constant(20)
+  >>> tf.get_static_value(tf.add(a, b))
+  30
+
+  >>> # `tf.Variable` is not supported.
+  >>> c = tf.Variable(30)
+  >>> print(tf.get_static_value(c))
+  None
+
+  Using `partial` option is most relevant when calling `get_static_value` inside
+  a `tf.function`. Setting it to `True` will return the results but for the
+  values that cannot be evaluated will be `None`. For example:
+
+  ```python
+  class Foo(object):
+    def __init__(self):
+      self.a = tf.Variable(1)
+      self.b = tf.constant(2)
+
+    @tf.function
+    def bar(self, partial):
+      packed = tf.raw_ops.Pack(values=[self.a, self.b])
+      static_val = tf.get_static_value(packed, partial=partial)
+      tf.print(static_val)
+
+  f = Foo()
+  f.bar(partial=True)  # `array([None, array(2, dtype=int32)], dtype=object)`
+  f.bar(partial=False)  # `None`
+  ```
+
   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