Process serialization will fail if it contains an instance of ExitCode

[sphuber]

This is because the ExitCode was changed from simple tuple to a class in v1.2.0 which now causes yaml.dump to except

import yaml
from aiida.engine import ExitCode
exit_code = ExitCode()
yaml.dump(exit_code)

will raise

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-4-33b699827b3a> in <module>
----> 1 yaml.dump(exit_code)

~/.virtualenvs/aiida_dev/lib/python3.7/site-packages/yaml/__init__.py in dump(data, stream, Dumper, **kwds)
    288     If stream is None, return the produced string instead.
    289     """
--> 290     return dump_all([data], stream, Dumper=Dumper, **kwds)
    291 
    292 def safe_dump_all(documents, stream=None, **kwds):

~/.virtualenvs/aiida_dev/lib/python3.7/site-packages/yaml/__init__.py in dump_all(documents, stream, Dumper, default_style, default_flow_style, canonical, indent, width, allow_unicode, line_break, encoding, explicit_start, explicit_end, version, tags, sort_keys)
    276         dumper.open()
    277         for data in documents:
--> 278             dumper.represent(data)
    279         dumper.close()
    280     finally:

~/.virtualenvs/aiida_dev/lib/python3.7/site-packages/yaml/representer.py in represent(self, data)
     25 
     26     def represent(self, data):
---> 27         node = self.represent_data(data)
     28         self.serialize(node)
     29         self.represented_objects = {}

~/.virtualenvs/aiida_dev/lib/python3.7/site-packages/yaml/representer.py in represent_data(self, data)
     32 
     33     def represent_data(self, data):
---> 34         if self.ignore_aliases(data):
     35             self.alias_key = None
     36         else:

~/.virtualenvs/aiida_dev/lib/python3.7/site-packages/yaml/representer.py in ignore_aliases(self, data)
    137         if data is None:
    138             return True
--> 139         if isinstance(data, tuple) and data == ():
    140             return True
    141         if isinstance(data, (str, bytes, bool, int, float)):

~/code/aiida/env/dev/aiida-core/aiida/engine/processes/exit_code.py in __eq__(self, other)
     50 
     51     def __eq__(self, other):
---> 52         return all(getattr(self, attr) == getattr(other, attr) for attr in ['status', 'message', 'invalidates_cache'])
     53 
     54 

~/code/aiida/env/dev/aiida-core/aiida/engine/processes/exit_code.py in <genexpr>(.0)
     50 
     51     def __eq__(self, other):
---> 52         return all(getattr(self, attr) == getattr(other, attr) for attr in ['status', 'message', 'invalidates_cache'])
     53 
     54 

AttributeError: 'tuple' object has no attribute 'status'

[greschd]

I think your traceback is missing the last part:

AttributeError: 'tuple' object has no attribute 'status'

It seems the ExitCode is somehow converted to (and then compared to) a bare tuple, which doesn't have the status attribute.

[greschd]

Changing ExitCode.__eq__ to include the type seems to work:

def __eq__(self, other):
    return type(self) == type(other) and all(
        getattr(self, attr) == getattr(other, attr) for attr in ['status', 'message', 'invalidates_cache']
    )

EDIT: It seems namedtuple compares equal to a bare tuple as long as the content is the same - maybe we should do the same. Easiest way to achieve that would just be remove our custom __eq__ implementation.