Fix logical errors in Gurobi check

[lpsinger]

• Fix circular import (ImportError: cannot import name 'Model' from partially initialized module 'mip' (most likely due to a circular import))
• Fix logic for setting mip.gurobi.found flag

[CLAassistant]

All committers have signed the CLA.

[jurasofish]

Very clean, a couple of thoughts:

• Seems FileNotFoundError (as raised here) would be appropriate to catch instead of a ~~ wide~~ catch Exception, and perhaps log.info the message so it doesn't disappear into the void.

• If the user specifies Gurobi as the solver and it can't be imported they get a very unhelpful exception (previously that FileNotFoundError was produced)

>>> import mip
>>> m = mip.Model(solver_name='GRB')
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/Users/michael/git/python-mip/mip/model.py", line 84, in __init__
    self.solver = mip.gurobi.SolverGurobi(self, name, sense)
AttributeError: module 'mip.gurobi' has no attribute 'SolverGurobi'

[lpsinger]

Due to the bare except Exception: in the original code, that nice error message would never have been printed. The latest version I just pushed does away with the except Exception: clause.

[jurasofish]

Due to the bare except Exception: in the original code, that nice error message would never have been printed. The latest version I just pushed does away with the except Exception: clause.

i didn't notice that, thanks for pointing out. good to fix it :)

new changes result in a bunch of types and default values of the methods of the classes being defined under the else. should be super easy to fix by just moving a couple of things above the if lib_path is None.

import mip
m = mip.Model('GRB')
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/Users/michael/git/python-mip/mip/model.py", line 90, in __init__
    import mip.gurobi
  File "/Applications/PyCharm.app/Contents/plugins/python/helpers/pydev/_pydev_bundle/pydev_import_hook.py", line 21, in do_import
    module = self._system_import(name, *args, **kwargs)
  File "/Users/michael/git/python-mip/mip/gurobi.py", line 325, in <module>
    class SolverGurobi(Solver):
  File "/Users/michael/git/python-mip/mip/gurobi.py", line 326, in SolverGurobi
    def __init__(self, model: Model, name: str, sense: str, modelp: CData = ffi.NULL):
NameError: name 'CData' is not defined

[h-g-s]

Hi @lpsinger , thanks for your contribution ! I`m reviewing the patches. In the last modification (October 14) there are some large modifications in guroby.py in several methods. Are they necessary in your patch or it happened due to an automatic format ? If they are, it would be good perhaps to split in more patches with comments.

[lpsinger]

@h-g-s, try suppressing whitespace changes in your diff viewer. It's not as big as a change as it looks.

[lpsinger]

@h-g-s, the large diff is due to indenting a large portion of gurobi.py to be inside an if statement.

[lpsinger]

The Black formatting errors were there before my PR. Would you like me to open a separate PR to clean up those formatting errors first?

[h-g-s]

Yes, please use the black formatting and open a new PR.

On Oct 23, 2020, at 10:40 AM, Leo Singer notifications@github.com wrote:

The Black formatting errors were there before my PR. Would you like me to open a separate PR to clean up those formatting errors first?

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[lpsinger]

Actually, the Black errors were introduced by me. Now fixed.