update parallel example

- fixes #407

.meta/.readme.rst

@@ -284,7 +284,7 @@ of a neat one-line progress bar.
   ``tqdm(zip(a, b))`` should be replaced with ``zip(tqdm(a), b)`` or even
   ``zip(tqdm(a), tqdm(b))``.
 - `Hanging pipes in python2 <https://github.com/tqdm/tqdm/issues/359>`__:
-  when using ``tqdm`` on the CLI, you may need to use python 3.5+ for correct
+  when using ``tqdm`` on the CLI, you may need to use Python 3.5+ for correct
   buffering.
 
 If you come across any other difficulties, browse and file |GitHub-Issues|.
@@ -488,7 +488,8 @@ available to keep nested bars on their respective lines.
 
 For manual control over positioning (e.g. for multi-processing use),
 you may specify ``position=n`` where ``n=0`` for the outermost bar,
-``n=1`` for the next, and so on:
+``n=1`` for the next, and so on. However, it's best to check if `tqdm` can work
+without manual `position` first.
 
 .. code:: python
 
@@ -507,11 +508,10 @@ you may specify ``position=n`` where ``n=0`` for the outermost bar,
 
     if __name__ == '__main__':
         freeze_support()  # for Windows support
-        p = Pool(len(L), initializer=tqdm.set_lock, initargs=(tqdm.get_lock(),))
+        p = Pool(initializer=tqdm.set_lock, initargs=(tqdm.get_lock(),))
         p.map(progresser, L)
 
-Note that in python 3, threads do not require manual positioning,
-and ``tqdm.write`` is safe to use:
+Note that in Python 3, ``tqdm.write`` is thread-safe:
 
 .. code:: python
 

README.rst

@@ -284,7 +284,7 @@ of a neat one-line progress bar.
   ``tqdm(zip(a, b))`` should be replaced with ``zip(tqdm(a), b)`` or even
   ``zip(tqdm(a), tqdm(b))``.
 - `Hanging pipes in python2 <https://github.com/tqdm/tqdm/issues/359>`__:
-  when using ``tqdm`` on the CLI, you may need to use python 3.5+ for correct
+  when using ``tqdm`` on the CLI, you may need to use Python 3.5+ for correct
   buffering.
 
 If you come across any other difficulties, browse and file |GitHub-Issues|.
@@ -654,7 +654,8 @@ available to keep nested bars on their respective lines.
 
 For manual control over positioning (e.g. for multi-processing use),
 you may specify ``position=n`` where ``n=0`` for the outermost bar,
-``n=1`` for the next, and so on:
+``n=1`` for the next, and so on. However, it's best to check if `tqdm` can work
+without manual `position` first.
 
 .. code:: python
 
@@ -673,11 +674,10 @@ you may specify ``position=n`` where ``n=0`` for the outermost bar,
 
     if __name__ == '__main__':
         freeze_support()  # for Windows support
-        p = Pool(len(L), initializer=tqdm.set_lock, initargs=(tqdm.get_lock(),))
+        p = Pool(initializer=tqdm.set_lock, initargs=(tqdm.get_lock(),))
         p.map(progresser, L)
 
-Note that in python 3, threads do not require manual positioning,
-and ``tqdm.write`` is safe to use:
+Note that in Python 3, ``tqdm.write`` is thread-safe:
 
 .. code:: python
 

examples/parallel_bars.py

@@ -1,38 +1,41 @@
 from __future__ import print_function
 from time import sleep
 from tqdm import tqdm, trange
+from random import random
 from multiprocessing import Pool, freeze_support
 from concurrent.futures import ThreadPoolExecutor
 from functools import partial
 import sys
 
+NUM_SUBITERS = 9
+PY2 = sys.version_info[:1] <= (2,)
 
-L = list(range(9))[::-1]
 
-
-def progresser(n, auto_position=False):
-    interval = 0.001 / (len(L) - n + 2)
+def progresser(n, auto_position=True, write_safe=False):
+    interval = random() * 0.002 / (NUM_SUBITERS - n + 2)
     total = 5000
     text = "#{}, est. {:<04.2}s".format(n, interval * total)
     for _ in tqdm(range(total), desc=text, position=None if auto_position else n):
         sleep(interval)
     # NB: may not clear instances with higher `position` upon completion
     # since this worker may not know about other bars #796
-    if auto_position:
+    if write_safe:
         # we think we know about other bars (currently only py3 threading)
         if n == 6:
             tqdm.write("n == 6 completed")
 
-if sys.version_info[:1] > (2,):
-    progresser_thread = partial(progresser, auto_position=True)
-else:
-    progresser_thread = progresser
-
 
 if __name__ == '__main__':
     freeze_support()  # for Windows support
+    L = list(range(NUM_SUBITERS))[::-1]
+
+    print("Manual nesting")
+    for i in trange(16, desc="1"):
+        for _ in trange(16, desc="2 @ %d" % i, leave=i % 2):
+            sleep(0.01)
+
     print("Multi-processing")
-    p = Pool(len(L), initializer=tqdm.set_lock, initargs=(tqdm.get_lock(),))
+    p = Pool(initializer=tqdm.set_lock, initargs=(tqdm.get_lock(),))
     p.map(progresser, L)
 
     # unfortunately need ncols
@@ -41,10 +44,6 @@ def progresser(n, auto_position=False):
         ncols = t.ncols or 80
     print(("{msg:<{ncols}}").format(msg="Multi-threading", ncols=ncols))
 
-    with ThreadPoolExecutor(4) as p:
+    with ThreadPoolExecutor() as p:
+        progresser_thread = partial(progresser, write_safe=not PY2)
         p.map(progresser_thread, L)
-
-    print("Manual nesting")
-    for i in trange(16, desc="1"):
-        for _ in trange(16, desc="2 @ %d" % i, leave=i % 2):
-            sleep(0.01)