iPython，保存一个代码单元格的输出，并且在执行期间仍然正常显示输出

Question

所以，这个问题的通常答案是使用细胞魔法“%%caputre cap”，问题是它抑制了正常输出并显示它你必须在单元格执行后运行 "cap.show()" 。当运行ning 一个需要很长时间的单元格时，比如训练神经网络，这个特性就变成了一个令人头疼的问题。我怎样才能运行我的代码单元并像往常一样获得实时输出并且之后能够将其保存到 .txt 文件？

Answer 1

这不是 IPython/Jupyter-specific，但这是我为类似目的编写的上下文管理器：

import sys


class capture_stdout:
    """
    Context manager similar to `contextlib.redirect_stdout`, but
    different in that it:
      - temporarily writes stdout to other streams *in addition to*
        rather than *instead of* `sys.stdout`
      - accepts any number of streams and sends stdout to each
      - can optionally keep streams open after exiting context by
        passing `closing=False`

    Parameters
    ----------
    *streams : *`io.IOBase`
        stream(s) to receive data sent to `sys.stdout`

    closing : `bool`, optional
        if [default: `True`], close streams upon exiting the context
        block.
    """
    def __init__(self, *streams, closing=True):
        self.streams = streams
        self.closing = closing
        self.sys_stdout_write = sys.stdout.write

    def __enter__(self):
        sys.stdout.write = self._write
        if len(self.streams) == 1:
            return self.streams[0]
        return self.streams

    def __exit__(self, exc_type, exc_value, traceback):
        sys.stdout.write = self.sys_stdout_write
        if self.closing:
            for s in self.streams:
                s.close()

    def _write(self, data):
        for s in self.streams:
            s.write(data)
        self.sys_stdout_write(data)
        sys.stdout.flush()

您可以传递任意数量的流，它会实时写入除了常规 sys.stdout 之外的所有流。因此，例如，如果你想显示实时输出，捕获它以供稍后在你的代码中使用，并将它记录到一个文件中，你可以这样做：

from io import StringIO


with capture_stdout(StringIO(), open('logfile.txt', 'w')) as (mem_stream, file_stream):
    print('some really long output')
    # etc...
    stdout = mem_stream.getvalue()
    

print(f"in str: {stdout}")
with open('logfile.txt', 'r') as f:
    print(f"in file: {f.read()}")

some really long output

in str: some really long output

in file: some really long output

转变为具有相同作用的细胞魔法应该也不会太难。 Here 的 IPython 文档部分是关于定义自定义魔法的，如果您想试一试的话。

iPython，保存一个代码单元格的输出，并且在执行期间仍然正常显示输出

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