使用IPython的魔力运行单元格执行代码时捕获异常和中断(在异常上)

Question

当使用IPython的magick命令运行木星单元中的一些python命令时，如何捕获错误？

In [1]: from IPython import get_ipython
        from IPython.core.magics.namespace import NamespaceMagics
        from IPython.utils.capture import capture_output


In [2]: _nms = NamespaceMagics()
        _Jupyter = get_ipython()
        _nms.shell = _Jupyter.kernel.shell
        cell_capture = capture_output(stdout=True, stderr=True, display=True)

In [3]: cell = "y = z**2"

In [4]: with cell_capture:
            _nms.shell.run_cell(cell)
        
        print("This gets printed")

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-9-5330dcdc6092> in <module>
----> 1 y = z**2

NameError: name 'z' is not defined

This gets printed

除了使用exec运行单元格之外，还有什么方法可以打断我遇到NameError (或者其他任何Exception )？

编辑

我已经尝试过使用try....catch (但它不能解决这个问题)：

In [5]: try:
            with cell_capture:
                _nms.shell.run_cell(cell)
        except Exception:
            raise

        print("Something here")


NameError                                 Traceback (most recent call last)
<ipython-input-29-5330dcdc6092> in <module>
----> 1 y = z**2

NameError: name 'z' is not defined

Something here

编辑2

try:
    with cell_capture:
        print('Inside cell capture here')
        _nms.shell.run_cell(cell)
except NameError:
    print("I'm in NameError")
    raise NameError("something bad happened")

print("Something here")


NameError                                 Traceback (most recent call last)
<ipython-input-33-5330dcdc6092> in <module>
----> 1 y = z**2

NameError: name 'z' is not defined

Something here

Answer 1

调用InteractiveShell.run_cell()的结果是ExecutionResult的一个实例。它有"raise_error“方法，”如果成功是假的，则重新定义错误，否则什么也不做“。您可以捕获异常，处理它，并重新定位它(如果需要的话)。

with cell_capture:
    result = get_ipython().run_cell(cell)
    result.raise_error()

https://ipython.readthedocs.io/en/stable/api/generated/IPython.core.interactiveshell.html#IPython.core.interactiveshell.ExecutionResult

Answer 2

注意：get_ipython()和get_ipython().kernel.shell是同一个对象，因此get_ipython().run_cell(cell)与更长的链相同：

from IPython.core.interactiveshell import InteractiveShell, ExecutionResult
ishell:InteractiveShell = get_ipython()
print(id(ishell), id(ishell.kernel.shell))

(从技术上讲，get_ipython将返回ipykernel.zmqshell.ZMQInteractiveShell (木星)或google.colab._shell.Shell (Colab)，但它们都扩展了IPython.core.interactiveshell.InteractiveShell)

对我来说，这并没有通过shell.run_cell

from IPython.core.interactiveshell import InteractiveShell, ExecutionResult
from IPython.utils.capture import capture_output, CapturedIO
cell = 'print("hello world")\nraise ValueError("hello sun")'
shell:InteractiveShell = get_ipython()  # noqa `get_ipython` is present in notebooks
with capture_output(stdout=True, stderr=True, display=True) as captured: #: CapturedIO
    try:
        print('hello mercury')
        result:ExecutionResult = shell.run_cell(cell)
        print(captured.stdout)
        print(captured.stderr)
        print(captured.outputs)
    except Exception as error:
        print('hello world')
        print(type(error))

因为capture_output没有停止错误，所以它只会屏蔽它们：

cell = 'print("hello world")\nraise ValueError("hello sun")'
shell:InteractiveShell = get_ipython()  # noqa `get_ipython` is present in notebooks
with capture_output(stdout=False, stderr=True, display=False) as captured: #: CapturedIO
    result:ExecutionResult = shell.run_cell(cell)
print('hello jupyter') # this is never run.

因此，问题在shell.run_cell中是有问题的。检查它做了什么：

import inspect
print(inspect.getsource(shell.run_cell)))

将mro升级到InteractiveShell().run_cell

print(inspect.getsource(InteractiveShell.run_cell))

给予：

    result = None
try:
    result = self._run_cell(
        raw_cell, store_history, silent, shell_futures)
finally:
    self.events.trigger('post_execute')
    if not silent:
        self.events.trigger('post_run_cell', result)
return result

触发器引起了我的注意..。至少对于我的应用程序(跟踪错误)来说，这可以很好地获得错误：

def foo(result: ExecutionResult):
    pass

shell.events.callbacks['post_run_cell'].append(foo)