Error getting subprocess error with non-blocking mode

[jakul]

Accessing command.err a second time causes an exception

In [1]: import delegator

In [2]: command = delegator.run('echo a', block=False)

In [3]: command.err
Out[3]: 'a\n'

In [4]: command.err
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-5e568e65e1e2> in <module>()
----> 1 command.err

~/.virtualenvs/service-mailer/lib/python3.6/site-packages/delegator.py in err(self)
    114             return self.__err
    115         else:
--> 116             return self._pexpect_out
    117
    118     @property

~/.virtualenvs/service-mailer/lib/python3.6/site-packages/delegator.py in _pexpect_out(self)
     82             result += self.subprocess.before
     83         if self.subprocess.after:
---> 84             result += self.subprocess.after
     85
     86         result += self.subprocess.read()

TypeError: must be str, not type

The cause is that self.subprocess.after becomes <class 'pexpect.exceptions.EOF'> after the first command.err

[jakul]

I've just checked the docs and found out that I shouldn't use command.err with non-blocking mode. Maybe the correct fix for this bug it so update the err function to not even try to read the error streams in non-blocking mode?

[ParthS007]

Closing due to inactivity :+1:

[timofurrer]

I'm re-opening this because there is actually a PR for it.

@jakul I think #62 fixed your issue, too. Can you please double check?

[jakul]

@timofurrer The behaviour is better, but still not correct.

In [1]: import delegator

In [2]: command = delegator.run('echo a', block=False)

In [3]: command.err
Out[3]: 'a\n'

In [4]: command.err
Out[4]: 'a\n'

In [5]: command.err
Out[5]: ''

In [6]: command.err
Out[6]: ''

Now command.err has a different the first and second times I call it, compared to the 3rd, 4th etc.

[timofurrer]

It's any ways strange that you get an output at all for command.err. It seems to work fine when you try to get the stdout from command.out.

[timofurrer]

I've just commited https://github.com/kennethreitz/delegator.py/commit/ad67b14232cd54a36b60afc6b02a3e8a1e75cca2 with which command.err is cached properly, but doesn't actually return stderr but stdout (which was already the case before this change. I'll have a look at how to change that behavior, too)