code: def force_backprop_mode():
      """Make a context manager which enables back-propagation.
  
      When you want to enable back-propagation in :func:`no_backprop_mode`, call
      this method. A :class:`~chainer.Variable` created in this context always
      has a computational graph unless overridden by deeper contexts. If you call
      this method outside of :func:`no_backprop_mode` context, it changes
      nothing.
  
      In the following example, ``y`` has a computational graph and calling
      :func:`~chainer.Variable.backward` on ``y`` will compute and accumulate the
      gradients of the variables in the graph, in this case only ``x``.
  
      >>> x = chainer.Variable(np.array([1,], np.float32))
      >>> with chainer.no_backprop_mode():
      ...     with chainer.force_backprop_mode():
      ...         y = x + 1
      >>> y.backward()
      >>> x.grad
      array([1.], dtype=float32)
  
      .. note::
  
         ``chainer.force_backprop_mode()`` implicitly applies ChainerX's
         counterpart :func:`chainerx.force_backprop_mode()`, but not vice versa.
         Also, setting ``enable_backprop`` :ref:`configuration <configuration>`
         does not affect ChainerX.
  
      .. seealso::
  
         See :func:`chainer.no_backprop_mode` for details on disabled
         back-propagation mode.
  
      """
      c = configuration.using_config("enable_backprop", True)
      if chainerx.is_available():
          return _BackpropModeContext(
              (c, chainerx.force_backprop_mode())
          )
      return _BackpropModeContext((c,))
  
imports: from __future__ import absolute_import
  import warnings
  import weakref
  import six
  import chainer
  from chainer import backend
  from chainer.backends import cuda
  from chainer import configuration
  from chainer.function_hook import FunctionHook
  from chainer import function_node
  from chainer import variable
  import chainerx
label_desc: Use image node_id 2 for calling a global function with example usage: force_backprop_mode() and returns: _BackpropModeContext, _BackpropModeContext