Use dict as the ordered dict type (#824)

Co-authored-by: Franco Peschiera <[email protected]>

Author: MBradbury

pulp/pulp.py

@@ -141,24 +141,6 @@
 
 log = logging.getLogger(__name__)
 
-_DICT_TYPE = dict
-
-if sys.platform not in ["cli"]:
-    # iron python does not like an OrderedDict
-    try:
-        from odict import OrderedDict  # type: ignore[import-not-found]
-
-        _DICT_TYPE = OrderedDict  # type: ignore[misc]
-    except ImportError:
-        pass
-    try:
-        # python 2.7 or 3.1
-        from collections import OrderedDict
-
-        _DICT_TYPE = OrderedDict  # type: ignore[misc]
-    except ImportError:
-        pass
-
 try:
     import ujson as json  # type: ignore[import-untyped]
 except ImportError:
@@ -661,7 +643,7 @@ def unfixValue(self):
         self.bounds(self._lowbound_original, self._upbound_original)
 
 
-class LpAffineExpression(_DICT_TYPE):
+class LpAffineExpression(dict):
     """
     A linear combination of :class:`LpVariables<LpVariable>`.
     Can be initialised with the following:
@@ -1419,7 +1401,7 @@ def __init__(self, name="NoName", sense=const.LpMinimize):
             warnings.warn("Spaces are not permitted in the name. Converted to '_'")
             name = name.replace(" ", "_")
         self.objective: None | LpAffineExpression = None  # type: ignore[annotation-unchecked]
-        self.constraints: dict[str, LpConstraint] = _DICT_TYPE()  # type: ignore[annotation-unchecked]
+        self.constraints: dict[str, LpConstraint] = {}  # type: ignore[annotation-unchecked]
         self.name = name
         self.sense = sense
         self.sos1 = {}
@@ -1487,7 +1469,7 @@ def deepcopy(self):
         lpcopy = LpProblem(name=self.name, sense=self.sense)
         if self.objective is not None:
             lpcopy.objective = self.objective.copy()
-        lpcopy.constraints = _DICT_TYPE[str, LpConstraint]()
+        lpcopy.constraints = {}
         for k, v in self.constraints.items():
             lpcopy.constraints[k] = v.copy()
         lpcopy.sos1 = self.sos1.copy()