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.. currentmodule:: chainer

Upgrade Guide

This is a list of changes introduced in each release that users should be aware of when migrating from older versions. Most changes are carefully designed not to break existing code; however changes that may possibly break them are highlighted with a box.

Chainer v5

Persistent Values are Copied in Link.copyparams

:meth:`chainer.Link.copyparams` is a method to copy all parameters of the link to another link. This method can be used, for example, to copy parameters between two chains that partially share the same network structure to reuse pretrained weights.

Prior to Chainer v5, only parameters are copied between links. In Chainer v5, in addition to parameters, persistent values (see :doc:`guides/serializers` for details) are also copied between links. This is especially beneficial when copying parameters of :class:`~chainer.links.BatchNormalization`, as it uses persistent values to record running statistics.

You can skip copying persistent values by passing newly introduced copy_persistent=False option to :meth:`~chainer.Link.copyparams` so that it behaves as in Chainer v4.

FuncionNodes as Implementation Details

When calling a Chainer function such as :func:`~chainer.functions.relu`, a corresponding :class:`~chainer.FunctionNode` is created internally, defining the forward and backward procedures. These classes are no longer a part of the public interface and you are encouraged not to instantiate these objects directly, as their interfaces may change.

Updaters Automatically Call Optimizer.new_epoch

This change should affect only a minority of users (who call :meth:`~chainer.Optimizer.new_epoch` while using a trainer, or who implement their own :class:`` class).

Optimizers provide :meth:`~chainer.Optimizer.new_epoch` method, which can be used to change the behavior of optimizers depending on the current epoch number. Prior to Chainer v5, this method was expected to be called by users. In Chainer v5, updaters have been changed to call :meth:`~chainer.Optimizer.new_epoch` automatically. If you have been calling :meth:`~chainer.Optimizer.new_epoch` method manually while using a trainer (or an updater), you may need any of the following fixes:

If you implement your own :class:`` class, you may need to update your code to automatically call :meth:`~chainer.Optimizer.new_epoch` (you can refer to the changes introduced in #4608 to understand how to fix your updater).

Chainer v4

Introduction of Backend Namespace

We introduced chainer.backends subpackage for future support of various backend libraries other than NumPy and CuPy. By this change, chainer.cuda module is now moved to chainer.backends.cuda.

This does not break the existing code; you can safely continue to use chainer.cuda (e.g., from chainer import cuda) but it is now encouraged to use from chainer.backends import cuda instead.

Namespace Changes for Updaters

:class:`` and :class:`` are now moved to :class:`` and :class:`` respectively, to align with the namespace convention of other subpackages. See the discussion in #2982 for more details.

This change does not break the existing code; you can safely continue to use updater classes directly under but it is now encouraged to use instead.

Namespace Changes for Optimizer Hooks

:doc:`Optimizer hook functions <reference/optimizers>` are moved from chainer.optimizer.* to chainer.optimizer_hooks.*. For example, chainer.optimizer.WeightDecay is now located :class:`chainer.optimizer_hooks.WeightDecay`.

If the existing code is using hooks directly under chainer.optimizer, DeprecationWarning will be shown. You are now encouraged to use chainer.optimizer_hooks instead.

Prohibition of Mixed Use of Arrays on Different Devices in Function Arguments

Argument validation of functions is now strictened to check device consistency of argument variables to provide better error messages to users. Suppose the following code:

v1 = chainer.Variable(np.arange(10, dtype=np.float32))      # CPU
v2 = chainer.Variable(cupy.arange(10, dtype=cupy.float32))  # GPU

# The line below raises an exception, because arguments are on different device.
F.maximum(v1, v2)

Prior to v4, the above code raises an exception like ValueError: object __array__ method not producing an array, which was difficult to understand. In v4, the error message would become TypeError: incompatible array types are mixed in the forward input (Maximum). This kind of error usually occurs by mistake (for example, not performing to_gpu for some variables).


As the argument validation is strictened, call of functions intentionally mixing NumPy/CuPy arrays in arguments will not work in Chainer v4. Please transfer all arrays to the same device before calling functions.

References to Function Nodes Not Retained in TimerHook and CupyMemoryProfilerHook

To reduce memory consumption, references to the function nodes will no longer be retained in the :class:`chainer.function_hooks.CupyMemoryProfileHook` and :class:`chainer.function_hooks.TimerHook`. See the discussion in #4300 for more details.


The existing code using function nodes retained in call_history attribute of these hooks will not work. The first element of call_history became the name of the function, instead of the function node instance itself. You can define your own function hook if you need to access the function node instances.

Update of Docker Images

Chainer official Docker images (see :doc:`install` for details) are now updated to use CUDA 8.0 and cuDNN 6.0. This change was introduced because CUDA 7.5 does not support NVIDIA Pascal GPUs.

To use these images, you may need to upgrade the NVIDIA driver on your host. See Requirements of nvidia-docker for details.

CuPy v4

Chainer v4 requires CuPy v4 if you need GPU support. Please see the Upgrade Guide for CuPy v4 for details.

Chainer v3

Introduction of New-style Functions

This release introduces new-style functions (classes inheriting from :class:`FunctionNode`) that support double backward (gradient of gradient). See the Release Note for v3.0.0 for the usage of this feature.

Many of :doc:`reference/functions` are already migrated to new-style, although some of functions are still old-style (classes inheriting from :class:`Function`). We are going to migrate more old-style functions to new-style in upcoming minor releases.

This does not break the existing code. Old-style functions (classes inheriting from :class:`Function`) are still supported in v3 and future versions of Chainer.

If you are going to write new functions, it is encouraged to use :class:`FunctionNode` to support double backward.


Users relying on undocumented function APIs (directly instantiating old-style classes) may experience an error like TypeError: 'SomeFunction' object is not callable after upgrading to v3. Please use the function APIs documented in :doc:`reference/functions`.

Changed Behavior of matmul Function

The behavior of :func:`chainer.functions.matmul` has been changed to behave like the corresponding NumPy function (:func:`numpy.matmul`). See the discussion in #2426 for more details.


The existing code using :func:`chainer.functions.matmul` may require modification to work with Chainer v3.

Also note that :func:`chainer.functions.batch_matmul` is now deprecated by this change. You can rewrite it using :func:`chainer.functions.matmul`.

Removed use_cudnn Argument in spatial_transformer_grid and spatial_transformer_sampler Functions

use_cudnn argument has been removed from :func:`chainer.functions.spatial_transformer_grid` and :func:`chainer.functions.spatial_transformer_sampler`. See the discussion in #2955 for more details.


The existing code using use_cudnn argument of :func:`chainer.functions.spatial_transformer_grid` and :func:`chainer.functions.spatial_transformer_sampler` require modification to work with Chainer v3. Please use the configuration context (e.g., with chainer.using_config('use_cudnn', 'auto'):) to enable or disable use of cuDNN. See :ref:`configuration` for details.

CuPy v2

Chainer v3 requires CuPy v2 if you need GPU support. Please see the Upgrade Guide for CuPy v2 for details.

Chainer v2

See :doc:`upgrade_v2` for the changes introduced in Chainer v2.

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