Only set random seed on purpose

Author: colin

pymc3/sampling.py

@@ -80,7 +80,7 @@ def assign_step_methods(model, step=None, methods=(NUTS, HamiltonianMC, Metropol
 
 
 def sample(draws, step=None, start=None, trace=None, chain=0, njobs=1, tune=None,
-           progressbar=True, model=None, random_seed=None):
+           progressbar=True, model=None, random_seed=-1):
     """
     Draw a number of samples using the given step method.
     Multiple step methods supported via compound step method
@@ -116,8 +116,8 @@ def sample(draws, step=None, start=None, trace=None, chain=0, njobs=1, tune=None
     tune : int
         Number of iterations to tune, if applicable (defaults to None)
     progressbar : bool
-        Whether or not to display a progress bar in the command line. The 
-        bar shows the percentage of completion, the sampling speed in 
+        Whether or not to display a progress bar in the command line. The
+        bar shows the percentage of completion, the sampling speed in
         samples per second (SPS), and the estimated remaining time until
         completion ("expected time of arrival"; ETA).
     model : Model (optional if in `with` context)
@@ -156,7 +156,7 @@ def sample(draws, step=None, start=None, trace=None, chain=0, njobs=1, tune=None
 
 
 def _sample(draws, step=None, start=None, trace=None, chain=0, tune=None,
-            progressbar=True, model=None, random_seed=None):
+            progressbar=True, model=None, random_seed=-1):
     sampling = _iter_sample(draws, step, start, trace, chain,
                             tune, model, random_seed)
     progress = progress_bar(draws)
@@ -170,7 +170,7 @@ def _sample(draws, step=None, start=None, trace=None, chain=0, tune=None,
 
 
 def iter_sample(draws, step, start=None, trace=None, chain=0, tune=None,
-                model=None, random_seed=None):
+                model=None, random_seed=-1):
     """
     Generator that returns a trace on each iteration using the given
     step method.  Multiple step methods supported via compound step
@@ -215,10 +215,11 @@ def iter_sample(draws, step, start=None, trace=None, chain=0, tune=None,
 
 
 def _iter_sample(draws, step, start=None, trace=None, chain=0, tune=None,
-                 model=None, random_seed=None):
+                 model=None, random_seed=-1):
     model = modelcontext(model)
     draws = int(draws)
-    seed(random_seed)
+    if random_seed != -1:
+        seed(random_seed)
     if draws < 1:
         raise ValueError('Argument `draws` should be above 0.')
 

pymc3/tests/test_sampling.py

@@ -24,6 +24,15 @@ def setUp(self):
         super(TestSample, self).setUp()
         self.model, self.start, self.step, _ = simple_init()
 
+    def test_sample_does_not_set_seed(self):
+        random_numbers = []
+        for _ in range(2):
+            np.random.seed(1)
+            with self.model:
+                pm.sample(1)
+                random_numbers.append(np.random.random())
+        self.assertEqual(random_numbers[0], random_numbers[1])
+
     def test_sample(self):
         test_njobs = [1]
         with self.model: