```json
{
  "sym_variables": [
    ("x1", "fences"),
    ("x2", "doors")
  ],
  "objective_function": "Maximize 200*x1 + 100*x2",
  "constraints": [
    "2*x1 + 5*x2 <= 400",
    "10*x1 + 1*x2 <= 500",
    "x1 >= 0",
    "x2 >= 0"
  ]
}
```

```python
import gurobipy as gp

try:
    # Create a new model
    m = gp.Model("steel_shop")

    # Create variables
    fences = m.addVar(vtype=gp.GRB.CONTINUOUS, name="fences")
    doors = m.addVar(vtype=gp.GRB.CONTINUOUS, name="doors")


    # Set objective function
    m.setObjective(200 * fences + 100 * doors, gp.GRB.MAXIMIZE)

    # Add constraints
    m.addConstr(2 * fences + 5 * doors <= 400, "stainless_steel_constraint")
    m.addConstr(10 * fences + 1 * doors <= 500, "aluminum_constraint")
    m.addConstr(fences >= 0, "fences_nonnegative")
    m.addConstr(doors >= 0, "doors_nonnegative")


    # Optimize model
    m.optimize()

    # Print results
    for v in m.getVars():
        print('%s %g' % (v.varName, v.x))

    print('Obj: %g' % m.objVal)

except gp.GurobiError as e:
    print('Error code ' + str(e.errno) + ': ' + str(e))

except AttributeError:
    print('Encountered an attribute error')

```
