<br />

|---|
| [![](https://www.tensorflow.org/images/GitHub-Mark-32px.png) View source on GitHub](https://github.com/tensorflow/tensorflow/blob/v2.21.0/tensorflow/python/ops/control_flow_case.py#L33-L135) |

Create a case operation.

    tf.case(
        pred_fn_pairs,
        default=None,
        exclusive=False,
        strict=False,
        name='case'
    )

### Used in the notebooks

| Used in the tutorials |
|---|
| - [Tutorial on Multi Armed Bandits in TF-Agents](https://www.tensorflow.org/agents/tutorials/bandits_tutorial) |

See also [`tf.switch_case`](https://www.tensorflow.org/api_docs/python/tf/switch_case).

The `pred_fn_pairs` parameter is a list of pairs of size N.
Each pair contains a boolean scalar tensor and a python callable that
creates the tensors to be returned if the boolean evaluates to True.
`default` is a callable generating a list of tensors. All the callables
in `pred_fn_pairs` as well as `default` (if provided) should return the same
number and types of tensors.

If `exclusive==True`, all predicates are evaluated, and an exception is
thrown if more than one of the predicates evaluates to `True`.
If `exclusive==False`, execution stops at the first predicate which
evaluates to True, and the tensors generated by the corresponding function
are returned immediately. If none of the predicates evaluate to True, this
operation returns the tensors generated by `default`.

[`tf.case`](https://www.tensorflow.org/api_docs/python/tf/case) supports nested structures as implemented in
[`tf.nest`](https://www.tensorflow.org/api_docs/python/tf/nest). All of the callables must return the same (possibly nested) value
structure of lists, tuples, and/or named tuples. Singleton lists and tuples
form the only exceptions to this: when returned by a callable, they are
implicitly unpacked to single values. This behavior is disabled by passing
`strict=True`.

**Example 1:**

#### Pseudocode:

    if (x < y) return 17;
    else return 23;

#### Expressions:

    f1 = lambda: tf.constant(17)
    f2 = lambda: tf.constant(23)
    r = tf.case([(tf.less(x, y), f1)], default=f2)

**Example 2:**

#### Pseudocode:

    if (x < y && x > z) raise OpError("Only one predicate may evaluate to True");
    if (x < y) return 17;
    else if (x > z) return 23;
    else return -1;

#### Expressions:

    def f1(): return tf.constant(17)
    def f2(): return tf.constant(23)
    def f3(): return tf.constant(-1)
    r = tf.case([(tf.less(x, y), f1), (tf.greater(x, z), f2)],
             default=f3, exclusive=True)

<br />

<br />

<br />

| ## Args ||
|---|---|
| `pred_fn_pairs` | List of pairs of a boolean scalar tensor and a callable which returns a list of tensors. |
| `default` | Optional callable that returns a list of tensors. |
| `exclusive` | True iff at most one predicate is allowed to evaluate to `True`. |
| `strict` | A boolean that enables/disables 'strict' mode; see above. |
| `name` | A name for this operation (optional). |

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<br />

| ## Returns ||
|---|---|
| The tensors returned by the first pair whose predicate evaluated to True, or those returned by `default` if none does. ||

<br />

<br />

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<br />

| ## Raises ||
|---|---|
| `TypeError` | If `pred_fn_pairs` is not a list/tuple. |
| `TypeError` | If `pred_fn_pairs` is a list but does not contain 2-tuples. |
| `TypeError` | If `fns[i]` is not callable for any i, or `default` is not callable. |

<br />

<br />

## v2 compatibility

<br />

`pred_fn_pairs` could be a dictionary in v1. However, tf.Tensor and
tf.Variable are no longer hashable in v2, so cannot be used as a key for a
dictionary. Please use a list or a tuple instead.

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