tf.compat.v1.variable_scope

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A context manager for defining ops that creates variables (layers).

tf.compat.v1.variable_scope(
    name_or_scope,
    default_name=None,
    values=None,
    initializer=None,
    regularizer=None,
    caching_device=None,
    partitioner=None,
    custom_getter=None,
    reuse=None,
    dtype=None,
    use_resource=None,
    constraint=None,
    auxiliary_name_scope=True
)

Description

This context manager validates that the (optional) values are from the same graph, ensures that graph is the default graph, and pushes a name scope and a variable scope.

If name_or_scope is not None, it is used as is. If name_or_scope is None, then default_name is used. In that case, if the same name has been previously used in the same scope, it will be made unique by appending _N to it.

Variable scope allows you to create new variables and to share already created ones while providing checks to not create or share by accident. For details, see the Variable Scope How To, here we present only a few basic examples.

The Variable Scope works as expected when the Eager Execution is Disabled.

tf.compat.v1.disable_eager_execution()

Simple example of how to create a new variable:

with tf.compat.v1.variable_scope("foo"):
    with tf.compat.v1.variable_scope("bar"):
        v = tf.compat.v1.get_variable("v", [1])
        assert v.name == "foo/bar/v:0"

Simple example of how to reenter a premade variable scope safely:

with tf.compat.v1.variable_scope("foo") as vs:
  pass

# Re-enter the variable scope.
with tf.compat.v1.variable_scope(vs,
                       auxiliary_name_scope=False) as vs1:
  # Restore the original name_scope.
  with tf.name_scope(vs1.original_name_scope):
      v = tf.compat.v1.get_variable("v", [1])
      assert v.name == "foo/v:0"
      c = tf.constant([1], name="c")
      assert c.name == "foo/c:0"

Keep in mind that the counters for default_name are discarded once the parent scope is exited. Therefore when the code re-enters the scope (for instance by saving it), all nested default_name counters will be restarted.

For instance:

with tf.compat.v1.variable_scope("foo") as vs:
  with tf.compat.v1.variable_scope(None, default_name="bar"):
    v = tf.compat.v1.get_variable("a", [1])
    assert v.name == "foo/bar/a:0", v.name
  with tf.compat.v1.variable_scope(None, default_name="bar"):
    v = tf.compat.v1.get_variable("b", [1])
    assert v.name == "foo/bar_1/b:0"

with tf.compat.v1.variable_scope(vs):
  with tf.compat.v1.variable_scope(None, default_name="bar"):
    v = tf.compat.v1.get_variable("c", [1])
    assert v.name == "foo/bar/c:0"   # Uses bar instead of bar_2!

Basic example of sharing a variable AUTO_REUSE:

def foo():
  with tf.compat.v1.variable_scope("foo", reuse=tf.compat.v1.AUTO_REUSE):
    v = tf.compat.v1.get_variable("v", [1])
  return v

v1 = foo()  # Creates v.
v2 = foo()  # Gets the same, existing v.
assert v1 == v2

Basic example of sharing a variable with reuse=True:

with tf.compat.v1.variable_scope("foo"):
    v = tf.compat.v1.get_variable("v", [1])
with tf.compat.v1.variable_scope("foo", reuse=True):
    v1 = tf.compat.v1.get_variable("v", [1])
assert v1 == v

Sharing a variable by capturing a scope and setting reuse:

with tf.compat.v1.variable_scope("foo") as scope:
    v = tf.compat.v1.get_variable("v", [1])
    scope.reuse_variables()
    v1 = tf.compat.v1.get_variable("v", [1])
assert v1 == v

To prevent accidental sharing of variables, we raise an exception when getting an existing variable in a non-reusing scope.

with tf.compat.v1.variable_scope("foo"):
    v = tf.compat.v1.get_variable("v", [1])
    v1 = tf.compat.v1.get_variable("v", [1])
    #  Raises ValueError("... v already exists ...").

Similarly, we raise an exception when trying to get a variable that does not exist in reuse mode.

with tf.compat.v1.variable_scope("foo", reuse=True):
    v = tf.compat.v1.get_variable("v", [1])
    #  Raises ValueError("... v does not exists ...").

Note that the reuse flag is inherited: if we open a reusing scope, then all its sub-scopes become reusing as well.

A note about name scoping: Setting reuse does not impact the naming of other ops such as mult. See related discussion on github#6189

Note that up to and including version 1.0, it was allowed (though explicitly discouraged) to pass False to the reuse argument, yielding undocumented behaviour slightly different from None. Starting at 1.1.0 passing None and False as reuse has exactly the same effect.

A note about using variable scopes in multi-threaded environment: Variable scopes are thread local, so one thread will not see another thread's current scope. Also, when using default_name, unique scopes names are also generated only on a per thread basis. If the same name was used within a different thread, that doesn't prevent a new thread from creating the same scope. However, the underlying variable store is shared across threads (within the same graph). As such, if another thread tries to create a new variable with the same name as a variable created by a previous thread, it will fail unless reuse is True.

Further, each thread starts with an empty variable scope. So if you wish to preserve name prefixes from a scope from the main thread, you should capture the main thread's scope and re-enter it in each thread. For e.g.

main_thread_scope = variable_scope.get_variable_scope()

# Thread's target function:
def thread_target_fn(captured_scope):
  with variable_scope.variable_scope(captured_scope):
    # .... regular code for this thread


thread = threading.Thread(target=thread_target_fn, args=(main_thread_scope,))

Methods

__enter__

View source

__enter__()

__exit__

View source

__exit__(
    type_arg, value_arg, traceback_arg
)