logging.FileHandler diff Py2 v Py3

[Peter Otten]

Paul Moore wrote:

> On 3 April 2018 at 17:54, Peter Otten <__peter__ at web.de> wrote:
>> I think the culprit is io.open() rather than the logging module. Why does
>>
>>>>> io.open("/dev/stderr", "a")
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>> OSError: [Errno 29] Illegal seek
>>
>> even try to seek()?
> 
> Because it's append mode so it needs to go to the end?

I expected that to be handled by the C library, and in C there is no error:

$ cat open_stderr_in_appendmode.c
#include <stdio.h>

main()
{
  FILE * stderr = fopen("/dev/stderr", "a");
  if (stderr == 0)
    {
      printf("failed\n");
    }
  else
    {
      printf("succeded\n");
      fprintf(stderr, "\nthis goes to stderr\n");
      fclose(stderr);
    }
}
$ gcc open_stderr_in_appendmode.c
$ ./a.out
succeded

this goes to stderr

The same goes for Py2's built-in and codecs.open():

$ python
Python 2.7.6 (default, Nov 23 2017, 15:49:48) 
[GCC 4.8.4] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import codecs
>>> import io
>>> with open("/dev/stderr", "a") as f: f.write("works\n")
... 
works
>>> with codecs.open("/dev/stderr", "a") as f: f.write("works\n")
... 
works
>>> with io.open("/dev/stderr", "a") as f: f.write("works\n")
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 29] Illegal seek
>>>

So io.open() really seems to do its own thing, and differently.