Reapply fix for #86 which was unintentionally reverted by commit id #e6620759fada127a1ef4cb2336d4ad9f8c000910

This will allow the fastai package to run with Python 3.6 which doesn't have the
mp_context parameter in the list of arguments to ProcessPoolExecutor,
which was introduced only in Python 3.7.
See https://docs.python.org/3/library/concurrent.futures.html#processpoolexecutor

Author: butchland

fastcore/utils.py

@@ -685,13 +685,12 @@ def _call(lock, pause, n, g, item):
 # Cell
 class ProcessPoolExecutor(concurrent.futures.ProcessPoolExecutor):
     "Same as Python's ProcessPoolExecutor, except can pass `max_workers==0` for serial execution"
-    def __init__(self, max_workers=defaults.cpus, on_exc=print, pause=0,
-                 mp_context=None, initializer=None, initargs=(),):
+    def __init__(self, max_workers=defaults.cpus, on_exc=print, pause=0, **kwargs):
         if max_workers is None: max_workers=defaults.cpus
         store_attr()
         self.not_parallel = max_workers==0
         if self.not_parallel: max_workers=1
-        super().__init__(max_workers, mp_context=mp_context, initializer=initializer, initargs=initargs)
+        super().__init__(max_workers, **kwargs)
 
     def map(self, f, items, timeout=None, chunksize=1, *args, **kwargs):
         self.lock = Manager().Lock()

nbs/02_utils.ipynb

@@ -3577,13 +3577,12 @@
     "#export\n",
     "class ProcessPoolExecutor(concurrent.futures.ProcessPoolExecutor):\n",
     "    \"Same as Python's ProcessPoolExecutor, except can pass `max_workers==0` for serial execution\"\n",
-    "    def __init__(self, max_workers=defaults.cpus, on_exc=print, pause=0,\n",
-    "                 mp_context=None, initializer=None, initargs=(),):\n",
+    "    def __init__(self, max_workers=defaults.cpus, on_exc=print, pause=0, **kwargs):\n",
     "        if max_workers is None: max_workers=defaults.cpus\n",
     "        store_attr()\n",
     "        self.not_parallel = max_workers==0\n",
     "        if self.not_parallel: max_workers=1\n",
-    "        super().__init__(max_workers, mp_context=mp_context, initializer=initializer, initargs=initargs)\n",
+    "        super().__init__(max_workers, **kwargs)\n",
     "\n",
     "    def map(self, f, items, timeout=None, chunksize=1, *args, **kwargs):\n",
     "        self.lock = Manager().Lock()\n",