tupledict behavior changed from version 10 to 11

Answered

Christian Ruf

February 23, 2024 18:37

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In version 10, tupledict.keys() returns a tuplelist. In version 11, it returns dictkeys like regular Python dictionaries do. Receiving a tuplelist is more convenient because one can use its select function. I wonder why this has been changed, and if the old functionality is available via some other function.

 

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• Python

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  Riley Clement

  • Gurobi Staff

  April 24, 2024 13:47 Edited

  Hi Christian,

  tupledicts were introduced many years ago when Python2 was the dominant Python version and Python3 was still very new.  As a result our tupledict was designed to be similar to Python2 dicts (as good practice would suggest).  Fast forward to the present time, where Python2 has reached end-of-life and rarely used, and we find that tupledict in gurobipy 10 no longer aligns with the Python3 dict object as much as we would like it to.  Eg, the result of calling dict.keys() is a dict_keys (a keys view) as you point out, and so we want to align to this behavior resulting in the change you notice in gurobipy 11.

  If you want to use gurobipy 11 with the existing functionality there are three options.  The first is to use an undocumented attribute:

  import gurobipy as gp
  gp.tupledict._legacy_tupledict_behavior = True

  Note that the preceding _ indicates this attribute is "private" and not really intended to be used, and the behavior or existence can be changed in future versions of gurobipy without warning or documentation.

  The second, safer option, is to cast the dict_views to a tuplelist when you want to, eg

  x = m.addVars(5)
  my_tuplelist_keys = gp.tuplelist(x.keys())

  The third option, which is the same vein as the second, is to monkeypatch this approach to happen automatically:

  import gurobipy as gp
  
  keys = gp.tupledict.keys
  
  def _keys(self):
      return gp.tuplelist(keys(self))
  
  gp.tupledict.keys = _keys

  After this code has run then tupledict.keys() will return a tuplelist.

  - Riley

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  Christian Ruf

  February 23, 2024 21:54

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  Thank you, Riley! 

  Will this be slow though? 

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  Riley Clement

  • Gurobi Staff

  February 24, 2024 02:11

  It will be slower, but I would be surprised if you were calling it so often that this had a meaningful impact.

  We can use timeit to get timings for a test (and then take the minimum to help eliminate noise).  In the test I'm calling .keys() on a tupledict with a million variables:

  import numpy as np
  import timeit
  
  setup = """
  import gurobipy as gp
  m = gp.Model()
  x = m.addVars(1000000)
  m.update()
  """
  
  statement= """
  x.keys()
  """
  
  print(np.min(timeit.repeat(stmt=statement, setup=setup, number=1, repeat=50)))

  On v10 this gave me 0.247 seconds and on v11 0.262 seconds (using my macbook).

  Switching out the setup:

  setup = """
  import gurobipy as gp
  
  keys = gp.tupledict.keys
  
  def _keys(self):
      return gp.tuplelist(keys(self))
  
  gp.tupledict.keys = _keys
  
  m = gp.Model()
  x = m.addVars(1000000)
  m.update()
  """

  and rerunning with v11 produced 0.305 seconds.  Using option 2) instead of monkeypatching will run slightly faster.

  Would you expect this to have consequences for your application?

  - Riley

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  Christian Ruf

  February 27, 2024 14:26

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  Thank you, Riley! I also think the impact will not be noticeable. 

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