allow string keys in x0 (#1431)

gpkit/constraints/sgp.py

@@ -205,14 +205,17 @@ def results(self):
 
     def _fill_x0(self, x0):
         "Returns a copy of x0 with subsitutions added."
-        x0 = KeyDict(x0) if x0 else KeyDict()
+        x0kd = KeyDict()
+        x0kd.varkeys = self.varkeys
+        if x0:
+            x0kd.update(x0)
         for key in self.varkeys:
-            if key in x0:
+            if key in x0kd:
                 continue  # already specified by input dict
             elif key in self.substitutions:
-                x0[key] = self.substitutions[key]
+                x0kd[key] = self.substitutions[key]
             # undeclared variables are handled by individual constraints
-        return x0
+        return x0kd
 
     def init_gp(self, substitutions, x0=None):
         "Generates a simplified GP representation for later modification"

gpkit/tests/t_model.py

@@ -533,17 +533,19 @@ def test_trivial_sp2(self):
     def test_sp_initial_guess_sub(self):
         x = Variable("x")
         y = Variable("y")
-        x0 = 2
+        x0 = 3
         y0 = 2
         with SignomialsEnabled():
             constraints = [y + x >= 4, y <= x]
         objective = x
         m = Model(objective, constraints)
         try:
-            sol = m.localsolve(x0={x: x0, y: y0}, verbosity=0,
-                               solver=self.solver)
+            sol = m.localsolve(x0={"x": x0, y: y0}, verbosity=0,
+                               mutategp=False, solver=self.solver)
         except TypeError:
             self.fail("Call to local solve with only variables failed")
+        self.assertEqual(m.program.gps[0].x0[x], 3)
+        self.assertEqual(m.program.gps[0].x0["y"], 2)
         self.assertAlmostEqual(sol(x), 2, self.ndig)
         self.assertAlmostEqual(sol["cost"], 2, self.ndig)