fix(apisimulation.py): fix exchange-related bugs (#99)

* __repr__ silently dropped the exchanges section (missing s +=)
* get_exchange(None) failed to return the first detected exchange
* ApiSimulation.load iterated the just-created empty exchanges dict instead of exchange_names, so exchanges and get_exchange() never returned a real exchange

Author: wpbonelli

autotest/test_interface.py

@@ -7,6 +7,7 @@
 from modflow_devtools.misc import set_dir
 
 from modflowapi import Callbacks, ModflowApi, run_simulation
+from modflowapi.extensions.apiexchange import ApiExchange
 from modflowapi.extensions.pakbase import AdvancedPackage, ArrayPackage, ListPackage
 
 data_pth = Path("../docs/examples/data")
@@ -293,6 +294,20 @@ def callback(sim, step):
             if len(sim.models) != 2:
                 raise AssertionError("Invalid number of models")
 
+            assert sim.exchange_names == ["gwf-gwf_1"]
+
+            exchange = sim.get_exchange()
+            assert isinstance(exchange, ApiExchange)
+
+            named_exchange = sim.get_exchange("gwf-gwf_1")
+            assert named_exchange is exchange
+
+            with pytest.raises(KeyError):
+                sim.get_exchange("not_a_real_exchange")
+
+            assert "Exchanges include" in repr(sim)
+            assert "gwf-gwf_1" in repr(sim)
+
     name = "two_models"
     sim_pth = data_pth / name
     test_pth = function_tmpdir / name

modflowapi/extensions/apisimulation.py

@@ -61,7 +61,7 @@ def __repr__(self):
         if self._exchanges:
             s += "\tExchanges include:\n"
             for name, exchange in self._exchanges.items():
-                f"\t\t{name}: {type(exchange)}\n"
+                s += f"\t\t{name}: {type(exchange)}\n"
 
         return s
 
@@ -256,8 +256,7 @@ def get_exchange(self, exchange_name=None):
             raise AssertionError("No exchanges are present in this simulation")
 
         if exchange_name is None:
-            for _, exg in self._exchanges:
-                return exg
+            return next(iter(self._exchanges.values()))
 
         else:
             if exchange_name in self._exchanges:
@@ -375,7 +374,7 @@ def load(mf6):
 
         # sim_packages: tdis, gwf-gwf, sln
         exchanges = {}
-        for exchange_name in exchanges:
+        for exchange_name in exchange_names:
             exchange = ApiExchange(mf6, exchange_name)
             exchanges[exchange_name.lower()] = exchange