Use Python 3 only

We were using some compatibility functions in nengo.utils.compat
out of habit, but since we are only supporting Python 3 they
were unnecessary.

nengo_loihi/builder.py

@@ -12,7 +12,6 @@
 from nengo.exceptions import BuildError
 from nengo.solvers import NoSolver, Solver
 from nengo.utils.builder import default_n_eval_points
-from nengo.utils.compat import iteritems
 import nengo.utils.numpy as npext
 
 from nengo_loihi.loihi_cx import (
@@ -841,7 +840,7 @@ def signal_probe(model, key, probe):
 @Builder.register(Probe)
 def build_probe(model, probe):
     # find the right parent class in `objtypes`, using `isinstance`
-    for nengotype, probeables in iteritems(probemap):
+    for nengotype, probeables in probemap.items():
         if isinstance(probe.obj, nengotype):
             break
     else:

nengo_loihi/loihi_cx.py

@@ -6,7 +6,7 @@
 
 import numpy as np
 from nengo.exceptions import BuildError, SimulationError
-from nengo.utils.compat import is_iterable, range
+from nengo.utils.compat import is_iterable
 
 from nengo_loihi.loihi_api import (
     BIAS_MAX,

nengo_loihi/simulator.py

@@ -8,7 +8,6 @@
 from nengo.exceptions import (
     BuildError, ReadonlyError, SimulatorClosed, ValidationError)
 from nengo.simulator import ProbeDict as NengoProbeDict
-from nengo.utils.compat import ResourceWarning
 
 from nengo_loihi.builder import Model
 from nengo_loihi.loihi_cx import CxGroup

nengo_loihi/splitter.py

@@ -3,7 +3,6 @@
 
 import nengo
 from nengo.exceptions import BuildError, SimulationError
-from nengo.utils.compat import iteritems
 import numpy as np
 
 from nengo_loihi import loihi_cx
@@ -74,9 +73,9 @@ def _add(obj, net):
                     "%s not moved or explicitly removed" % (obj,))
 
         # Process moves and adds
-        for obj, target in iteritems(self.moves):
+        for obj, target in self.moves.items():
             _add(obj, getattr(self, target))
-        for obj, target in iteritems(self.adds):
+        for obj, target in self.adds.items():
             _add(obj, getattr(self, target))
 
     def location(self, obj, default=None):

nengo_loihi/tests/test_splitter.py

@@ -1,6 +1,5 @@
 import pytest
 import nengo
-from nengo.utils.compat import iteritems, itervalues
 import numpy as np
 
 from nengo_loihi.config import add_params
@@ -147,7 +146,7 @@ def test_split_host_neurons_to_chip():
     def assert_split_correctly(split_conn):
         assert len(networks.adds) == 4
         added_types = sorted([(type(obj).__name__, location)
-                              for obj, location in iteritems(networks.adds)])
+                              for obj, location in networks.adds.items()])
         assert added_types == [
             ("ChipReceiveNeurons", "chip"),
             ("Connection", "chip"),
@@ -309,9 +308,9 @@ def test_split_host_to_learning_rule():
         "Connection", "Connection", "HostSendNode", "HostSendNode",
     ]
     assert off2on_ens in networks.removes
-    assert "ens_pes_target" in list(itervalues(networks.host2chip_senders))
+    assert "ens_pes_target" in list(networks.host2chip_senders.values())
     assert off2on_neurons in networks.removes
-    assert "neurons_pes_target" in list(itervalues(networks.host2chip_senders))
+    assert "neurons_pes_target" in list(networks.host2chip_senders.values())
 
 
 def test_place_probes():