PEP8 style, daemonizing child processes (#2747)

pymc3/sampling.py

@@ -654,14 +654,16 @@ def __init__(self, steppers, parallelize):
                 # configure a child process for each stepper
                 pm._log.info('Attempting to parallelize chains.')
                 import multiprocessing
-                for c,stepper in enumerate(steppers):
+                for c, stepper in enumerate(tqdm(steppers)):
                     slave_end, master_end = multiprocessing.Pipe()
                     stepper_dumps = pickle.dumps(stepper, protocol=4)
                     process = multiprocessing.Process(
                         target=self.__class__._run_slave,
                         args=(c, stepper_dumps, slave_end),
                         name='ChainWalker{}'.format(c)
                     )
+                    # we want the child process to exit if the parent is terminated
+                    process.daemon = True
                     # Starting the process might fail and takes time.
                     # By doing it in the constructor, the sampling progress bar
                     # will not be confused by the process start.
@@ -794,7 +796,7 @@ def _prepare_iter_population(draws, chains, step, start, parallelize, tune=None,
 
     # 1. prepare a BaseTrace for each chain
     traces = [_choose_backend(None, chain, model=model) for chain in chains]
-    for c,strace in enumerate(traces):
+    for c, strace in enumerate(traces):
         # initialize the trace size and variable transforms
         if len(strace) > 0:
             update_start_vals(start[c], strace.point(-1), model)
@@ -860,7 +862,7 @@ def _iter_population(draws, tune, popstep, steppers, traces, points):
                 updates = popstep.step(i == tune, points)
 
                 # apply the update to the points and record to the traces
-                for c,strace in enumerate(traces):
+                for c, strace in enumerate(traces):
                     if steppers[c].generates_stats:
                         points[c], states = updates[c]
                         if strace.supports_sampler_stats:
@@ -873,17 +875,17 @@ def _iter_population(draws, tune, popstep, steppers, traces, points):
                 # yield the state of all chains in parallel
                 yield traces
     except KeyboardInterrupt:
-        for c,strace in enumerate(traces):
+        for c, strace in enumerate(traces):
             strace.close()
             if hasattr(steppers[c], 'report'):
                 steppers[c].report._finalize(strace)
         raise
     except BaseException:
-        for c,strace in enumerate(traces):
+        for c, strace in enumerate(traces):
             strace.close()
         raise
     else:
-        for c,strace in enumerate(traces):
+        for c, strace in enumerate(traces):
             strace.close()
             if hasattr(steppers[c], 'report'):
                 steppers[c].report._finalize(strace)