python - file.write 仅在交互式 python session 退出时执行？

Question

我发现了一种我不理解的行为，希望有人能够阐明它。

它看起来像交互式 python session (都使用 ipython 并且直接调用 python3 cmd)仅在退出 session 时写入文件。

(ipython)dev:~$ ipython
Python 3.4.0 (default, Apr 11 2014, 13:05:11)
Type "copyright", "credits" or "license" for more information.

IPython 3.1.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: outfile = open('outfile','w')

In [2]: outfile.write('test')
Out[2]: 4

In [3]: outfile.close
Out[3]: <function TextIOWrapper.close>

In [4]: !ls -l outfile
-rw-rw-r-- 1 jjk3 jjk3 0 Jun 10 14:32 outfile

In [5]: quit
(ipython)dev:~$ ls -l outfile
-rw-rw-r-- 1 jjk3 jjk3 4 Jun 10 14:33 outfile
(ipython)dev:~$

这种行为是预期的吗？如果是这样为什么？

如果这种行为是意外的，知道为什么会这样吗？

Answer 1

您没有调用 close，因此文件仍然处于打开状态，直到您退出 shell:

outfile.close() # <- add parens

一旦你这样做了，你就会看到差异:

In [12]: outfile = open('outfile','w')    
In [13]:  outfile.write('test')    
In [14]:  outfile.close
Out[14]: <function close>    
In [15]: !ls -l outfile
-rw-rw-r-- 1 padraic padraic 0 Jun 10 22:41 outfile    
In [16]:  outfile.close()
In [17]: !ls -l outfile
-rw-rw-r-- 1 padraic padraic 4 Jun 10 22:41 outfile

您应该使用 with 打开文件并让它为您处理关闭操作:

In [18]: with open('outfile','w') as out:
   ....:     out.write("test")
   ....:        
In [19]: !ls -l outfile
-rw-rw-r-- 1 padraic padraic 4 Jun 10 22:43 outfile