Return true_fn() if the predicate pred is true else ``().

# Aliases:

• tf.compat.v2.cond

 tf.cond(
    pred,
    true_fn=None,
    false_fn=None,
    name=None
)

true_fn and false_fn both return lists of output tensors. true_fn and false_fn must have the same non-zero number and type of outputs. WARNING: Any Tensors or Operations created outside of true_fn and false_fn will be executed regardless of which branch is selected at runtime. Although this behavior is consistent with the dataflow model of TensorFlow, it has frequently surprised users who expected a lazier semantics. Consider the following simple program:

 z = tf.multiply(a, b)
result = tf.cond(x < y, lambda: tf.add(x, z), lambda: tf.square(y))

tf.multiplyIf x < y, the tf.add operation will be executed and tf.square operation will not be executed. Since z is needed for at least one branch of the cond, the operation is always executed, unconditionally.

Note that cond calls true_fn and false_fn exactly once (inside the call to cond, and not at all during Session.run()). cond stitches together the graph fragments created during the true_fn and false_fn calls with some additional graph nodes to ensure that the right branch gets executed depending on the value of ``. tf.cond supports nested structures as implemented in tensorflow.python.util.nest. Both true_fn and false_fn 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 true_fn and/or false_fn, they are implicitly unpacked to single values.

# Args:

• pred: A scalar determining whether to return the result of true_fn or false_fn.
• true_fn: The callable to be performed if pred is true.
• false_fn: The callable to be performed if pred is false.
• name: Optional name prefix for the returned tensors.

# Returns:

Tensors returned by the call to either true_fn or false_fn. If the callables return a singleton list, the element is extracted from the list.

# Raises:

• TypeError: if true_fn or false_fn is not callable.
• ValueError: if true_fn and false_fn do not return the same number of tensors, or return tensors of different types.

# Example:

 x = tf.constant(2)
y = tf.constant(5)
def f1(): return tf.multiply(x, 17)
def f2(): return tf.add(y, 23)
r = tf.cond(tf.less(x, y), f1, f2)
# r is set to f1().
# Operations in f2 (e.g., tf.add) are not executed.