Strange return values in nodes.py

[alexsavio]

Hi,

Today I ran into an error on the master branch and went to check the code.

I saw that the yield variables in:
https://github.com/nipy/nipype/blob/master/nipype/pipeline/engine/nodes.py#L1154
don't make sense.
The thing is that err will be None always, if the exception is raised and then err has a value the function will raise that exception instead of yield-ing the values.

I am putting this issue here because I don't know what is the objective of this function. I guess that the code inside the exception needs an 'else: pass' and maybe a finally statement.

[alexsavio]

I have checked this with a colleague and maybe it is because I am using Python 3.5 and this is not being tested.
This does work on Python 2.7 though.

The exception raised when I run it is:

base.py report_crash: INFO Traceback (most recent call last):
  File "/home/alexandre/Software/nipype/nipype/pipeline/plugins/multiproc.py", line 19, in run_node
    result['result'] = node.run(updatehash=updatehash)
  File "/home/alexandre/Software/nipype/nipype/pipeline/engine/nodes.py", line 392, in run
    self._run_interface()
  File "/home/alexandre/Software/nipype/nipype/pipeline/engine/nodes.py", line 1301, in _run_interface
    updatehash=updatehash))
  File "/home/alexandre/Software/nipype/nipype/pipeline/engine/nodes.py", line 1164, in _collate_results
    for i, node, err in nodes:
  File "/home/alexandre/Software/nipype/nipype/pipeline/engine/nodes.py", line 1157, in _node_runner
    yield i, node, err
UnboundLocalError: local variable 'err' referenced before assignment

My impression is that the err variable is being deleted after the except statement (which is strange). So I made the following and now I see that the underlying error comes from Matlab.

    def _node_runner(self, nodes, updatehash=False):
        for i, node in nodes:
            err = None
            try:
                node.run(updatehash=updatehash)
            except Exception as exc:
                if str2bool(self.config['execution']['stop_on_first_crash']):
                    self._result = node.result
                    raise
                else:
                    err = exc
            finally:
                yield i, node, err

[alexsavio]

Anyway, IMO this small modification in the _node_runner function makes it a bit easier to read. However the re-assignement err = exc is not needed for the finally block.

[alexsavio]

I have found an explanation on the matter here:
http://stackoverflow.com/questions/35545299/tracebacks-in-python-3-5

[alexsavio]

I've made a PR #1447 to fix this.

[ashgillman]

I am still getting this error, on Python 3.4.4, Nipype 12.0. I have had a look through the Python 3.5 release changes but I can't find reference to anything that would still cause this.

[ashgillman]

@alexsavio Your previous comment seems to fix. I threw into PR #1551