Restore Python 3.8 compatibility for dictionary merge

[hmenke]

The | operator requires Python 3.9, which would then exclude Ubuntu 20.04 and other distros with older Python.

[the-hampel]

Are we sure we are not using any other Python 3.9 features already? @merkelm @alberto-carta Otherwise we can of course restore backward compatibility. TRIQS itself states 3.6, but I think some parts require newer Python versions.

[hmenke]

I've been using solid_dmft on Ubuntu 20.04 which has Python 3.8. Unfortuantely I developed #61 on a machine with Python 3.10 and the CI also runs Python 3.10, so I did not notice the compatibility problem.

[the-hampel]

Would it be an option to just store the keyword directly in line 352 in self.solver_params , i.e.:

self.solver_params['random_seed'] = int(self.random_seed_generator(it=kwargs["it"], rank=mpi.rank))

[hmenke]

I would rather not overwrite solver_params['random_seed'] in-place, because that should be the value from read_config and if you overwrite this the wrong value might be serialized to the output file.

[the-hampel]

But the original solver_params that are stored in the h5 are owned by dmft_cylce, and stored from there to the h5, the dict withing the solid_dmft solver object is not used for storage. Or do you mean other output? I think that should be save to overwrite then no? At least I do not see a problem right now.

[hmenke]

Dictionaries (and lists) are reference types. They are not copied (unless explicitly using .copy()):

>>> a = { "foo": 1 }
>>> b = a
>>> b["foo"] = 2
>>> a
{'foo': 2}

[the-hampel]

Ah yes of course. Somehow I wasn't sure with a dict but you are of course right. Then we do not want to change it ;-)