[issue7784] patch for making list/insert at the top of the list avoid memmoves

[showell]

showell <showell30 at yahoo.com> added the comment:

Ok, found the offending line, now all tests pass.  

The use case where this patch will pay off the most is slicing your way through a list of tasks.  The toy program below gets about a 50x speedup.

	import time

	n = 800000

	lst = []
	for i in range(n):
		lst.append(i)

	t = time.time()
	for i in range(n):
		x = lst[:10]
		del lst[:10]

	print('time = ' + str(time.time() - t))
	print(len(lst))

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Added file: http://bugs.python.org/file16034/no_mem_penalty.diff

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<http://bugs.python.org/issue7784>
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