bpo-30296 Remove unnecessary tuples, lists, sets, and dicts (#1489)

* Replaced list(<generator expression>) with list comprehension
* Replaced dict(<generator expression>) with dict comprehension
* Replaced set(<list literal>) with set literal
* Replaced builtin func(<list comprehension>) with func(<generator
  expression>) when supported (e.g. any(), all(), tuple(), min(), &
  max())
diff --git a/Lib/multiprocessing/context.py b/Lib/multiprocessing/context.py
index a3d491b..c98ee43 100644
--- a/Lib/multiprocessing/context.py
+++ b/Lib/multiprocessing/context.py
@@ -261,7 +261,7 @@
             else:
                 return ['fork', 'spawn']
 
-DefaultContext.__all__ = list(x for x in dir(DefaultContext) if x[0] != '_')
+DefaultContext.__all__ = [x for x in dir(DefaultContext) if x[0] != '_']
 
 #
 # Context types for fixed start method