“ contextlib.redirect_stdout”不适用于Ipython

Question

I am working on Ipython like to get help info about os.stat and redirect the output to a plain markdown file:

In [57]: with contextlib.redirect_stdout(open("stat_help_docs.md", "w")):
    ...:     help(os.stat)
    ...:     
In [58]: os.stat("stat_help_docs.md").st_size
Out[58]: 1

The "stat_help_docs.md" is empty, it failed to write help docs to it.
However, If I tried in the Standard Python Interactive Mode:

>>> import os
>>> import contextlib
>>> with contextlib.redirect_stdout(open("another_stat_help_docs.md", "w")):
...     help(os.stat)
... 
>>> os.stat("another_stat_help_docs.md").st_size
919

It succeeded in write to the file.
I assume the problem might lie in the setting of Ipython,
Could please provide any hints to help dig in the problem?

Answer 1

You need flush the file write buffer:

In [9]: f = open('stat_help_docs.txt', 'w')


In [10]: with contextlib.redirect_stdout(f):
    ...:     help(os.stat)

In [11]: os.stat("stat_help_docs.txt").st_size
Out[11]: 0

In [12]: f.flush()

In [13]: os.stat("stat_help_docs.txt").st_size
Out[13]: 919

In the standard python shell, the file object gets recycled right after with context and the underlying write buffer is flushed, no idea why IPython shell holds extra references for the file object.

But IMO one shouldn't rely on GC to flush the write buffer, either use file obj as a context manager ( with open('...'): ) or flush explicitly.