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| |
| <h1 id="exception-handing-and-custom-error-types">Exception handing and custom error types</h1> |
| |
| <p>Apache MXNet v1.7 has added the custom error type support and as a result <code class="highlighter-rouge">MXNetError</code> is inherited from <code class="highlighter-rouge">RuntimeError</code> so it is possible to register a custom error type in the backend and prepend its error message. Then in the frontend, one can throw the exception of the registered error type.</p> |
| |
| <p>For example, we want the <code class="highlighter-rouge">transpose</code> operator defined in the C++ backend to throw <code class="highlighter-rouge">ValueError</code> type in the Python frontend. Therefore, in the C++ backend we can add this check:</p> |
| |
| <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>CHECK_EQ(axes_set.size(), axes.ndim()) << "ValueError: Repeated axis in transpose." |
| << " param.axes = " |
| << param.axes; |
| </code></pre></div></div> |
| |
| <p>so that on the frontend, when a problematic <code class="highlighter-rouge">transpose</code> call is made such as:</p> |
| |
| <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>from mxnet import np |
| |
| dat = np.random.normal(0, 1, (3, 4, 5)) |
| dat.transpose((0, 0, 1)) |
| </code></pre></div></div> |
| |
| <p>the following traceback will be produced:</p> |
| |
| <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>ValueError Traceback (most recent call last) |
| <ipython-input-3-3ad259b4e371> in <module> |
| ----> 1 dat.transpose((0, 0, 1)) |
| |
| ~/mxnet-distro/mxnet-build/python/mxnet/numpy/multiarray.py in transpose(self, *axes) |
| 1460 elif axes[0] is None: |
| 1461 axes = None |
| -> 1462 return _mx_np_op.transpose(self, axes=axes) |
| 1463 |
| 1464 def flip(self, *args, **kwargs): |
| ~/mxnet-distro/mxnet-build/python/mxnet/ndarray/register.py in transpose(a, axes, out, name, **kwargs) |
| |
| ~/mxnet-distro/mxnet-build/python/mxnet/_ctypes/ndarray.py in _imperative_invoke(handle, ndargs, keys, vals, out, is_np_op, output_is_list) |
| 105 c_str_array(keys), |
| 106 c_str_array([str(s) for s in vals]), |
| --> 107 ctypes.byref(out_stypes))) |
| 108 |
| 109 create_ndarray_fn = _np_ndarray_cls if is_np_op else _ndarray_cls |
| |
| ~/mxnet-distro/mxnet-build/python/mxnet/base.py in check_call(ret) |
| 271 """ |
| 272 if ret != 0: |
| --> 273 raise get_last_ffi_error() |
| 274 |
| 275 |
| ValueError: Traceback (most recent call last): |
| File "src/operator/numpy/np_matrix_op.cc", line 77 |
| |
| ValueError: Check failed: axes_set.size() == axes.ndim() (2 vs. 3) : Repeated axis in transpose. param.axes = [0,0,1] |
| </code></pre></div></div> |
| |
| <p>Note that as of writing this document, the following Python error types are supported:</p> |
| |
| <ul> |
| <li><code class="highlighter-rouge">ValueError</code></li> |
| <li><code class="highlighter-rouge">TypeError</code></li> |
| <li><code class="highlighter-rouge">AttributeError</code></li> |
| <li><code class="highlighter-rouge">IndexError</code></li> |
| <li><code class="highlighter-rouge">NotImplementedError</code></li> |
| </ul> |
| |
| <p>Check <a href="https://github.com/apache/incubator-mxnet/blob/master/python/mxnet/error.py">this</a> resource for more details |
| about Python supported error types that MXNet supports.</p> |
| |
| <h2 id="how-to-register-a-custom-error-type">How to register a custom error type</h2> |
| |
| <p>Here is the way to register a custom error type in Python frontend:</p> |
| |
| <div class="highlighter-rouge"><div class="highlight"><pre class="highlight"><code>import mxnet as mx |
| |
| @mx.error.register |
| class MyError(mx.MXNetError): |
| def __init__(self, msg): |
| super().__init__(msg) |
| </code></pre></div></div> |
| |
| <p>Then in the C++ backend, you can refer to <code class="highlighter-rouge">MyError</code> via:</p> |
| |
| <p><code class="highlighter-rouge">LOG(FATAL) << "MyError: this is a custom error message"</code></p> |
| |
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| </footer> |
| |
| |
| |
| |
| </body> |
| |
| </html> |
