fix parallel example extra line

- closes #477
- partially reverts 74e6eba
- Note 74e6eba breaks unit tests/behaviour for non-parallel cases.
  Automation for parallel cases is not possible since
  `tqdm.tqdm._instances` may not be populated in individual threads.

examples/parallel_bars.py

@@ -1,6 +1,6 @@
 from __future__ import print_function
 from time import sleep
-from tqdm import tqdm
+from tqdm import tqdm, trange
 from multiprocessing import Pool, freeze_support, RLock
 
 
@@ -11,7 +11,10 @@ def progresser(n):
     interval = 0.001 / (len(L) - n + 2)
     total = 5000
     text = "#{}, est. {:<04.2}s".format(n, interval * total)
-    for _ in tqdm(range(total), desc=text, position=n):
+    # NB: ensure position>0 to prevent printing '\n' on completion.
+    # `tqdm` can't autmoate this since this thread
+    # may not know about other bars in other threads #477.
+    for _ in tqdm(range(total), desc=text, position=n + 1):
         sleep(interval)
 
 
@@ -21,9 +24,15 @@ if __name__ == '__main__':
              initializer=tqdm.set_lock,
              initargs=(RLock(),))
     p.map(progresser, L)
-    print("\n" * len(L))
+    print('\n' * len(L))
 
     # alternatively, on UNIX, just use the default internal lock
     p = Pool(len(L))
     p.map(progresser, L)
-    print("\n" * len(L))
+    print('\n' * len(L))
+
+    # a manual test demonstrating automatic fix for #477 on one thread
+    for _ in trange(10, desc="1", position=1):
+        for _ in trange(10, desc="2", position=0):
+            sleep(0.01)
+    print('\n')

tqdm/_tqdm.py

@@ -1107,13 +1107,15 @@ Please use `tqdm_gui(...)` instead of `tqdm(..., gui=True)`
                     # stats for overall rate (no weighted average)
                     self.avg_time = None
                     self.sp(self.__repr__())
-                if pos is not None:
+                if pos:
                     self.moveto(-pos)
-                else:
+                elif not max([abs(getattr(i, "pos", 0))
+                              for i in self._instances] + [0]):
+                    # only if not nested (#477)
                     fp_write('\n')
             else:
                 self.sp('')  # clear up last bar
-                if pos is not None:
+                if pos:
                     self.moveto(-pos)
                 else:
                     fp_write('\r')