Change lambda value to float type for Exponential

Initially, ' Integers to negative integer powers are not allowed.' error would appear when I run the Exponential model. I read the doc file, and it says lam accepts float type only. 

I am not sure whether it is the python version issue or pymc3 version issue. Just want to point out something wrong and the way to fix it on my particular case.

Author: CloudandML

Chapter2_MorePyMC/Ch2_MorePyMC_PyMC3.ipynb

@@ -45,7 +45,7 @@
     "import pymc3 as pm\n",
     "\n",
     "with pm.Model() as model:\n",
-    "    parameter = pm.Exponential(\"poisson_param\", 1)\n",
+    "    parameter = pm.Exponential(\"poisson_param\", 1.0)\n",
     "    data_generator = pm.Poisson(\"data_generator\", parameter)"
    ]
   },
@@ -123,7 +123,7 @@
    ],
    "source": [
     "with pm.Model() as model:\n",
-    "    theta = pm.Exponential(\"theta\", 2)\n",
+    "    theta = pm.Exponential(\"theta\", 2.0)\n",
     "    data_generator = pm.Poisson(\"data_generator\", theta)"
    ]
   },
@@ -221,7 +221,7 @@
    ],
    "source": [
     "with pm.Model() as model:\n",
-    "    parameter = pm.Exponential(\"poisson_param\", 1, testval=0.5)\n",
+    "    parameter = pm.Exponential(\"poisson_param\", 1.0, testval=0.5)\n",
     "\n",
     "print(\"\\nparameter.tag.test_value =\", parameter.tag.test_value)"
    ]
@@ -296,8 +296,8 @@
    ],
    "source": [
     "with pm.Model() as model:\n",
-    "    lambda_1 = pm.Exponential(\"lambda_1\", 1)\n",
-    "    lambda_2 = pm.Exponential(\"lambda_2\", 1)\n",
+    "    lambda_1 = pm.Exponential(\"lambda_1\", 1.0)\n",
+    "    lambda_2 = pm.Exponential(\"lambda_2\", 1.0)\n",
     "    tau = pm.DiscreteUniform(\"tau\", lower=0, upper=10)\n",
     "\n",
     "new_deterministic_variable = lambda_1 + lambda_2"
@@ -1607,7 +1607,7 @@
     "x = np.ones(N, dtype=object)\n",
     "with pm.Model() as model:\n",
     "    for i in range(0, N):\n",
-    "        x[i] = pm.Exponential('x_%i' % i, (i+1)**2)"
+    "        x[i] = pm.Exponential('x_%i' % i, (i+1.0)**2)"
    ]
   },
   {