Commit714fb14

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Clarify how you would end up with None in programming.rst

Assigning `y.sort()` to a variable clarifies why you would end up with a `None`.

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Original file line number	Diff line number	Diff line change
@@ -481,9 +481,9 @@ object, whereas superficially similar operations (for example ``y = y + [10]``
`481`	`481`	and:func:`sorted(y) <sorted>`) create a new object. In general in Python (and in all cases
`482`	`482`	in the standard library) a method that mutates an object will return ``None``
`483`	`483`	`to help avoid getting the two types of operations confused. So if you`
`484`		-mistakenly write ``y.sort()`` thinkingit will give you a sorted copy of ``y``,
`485`		-you'll instead end up with ``None``, which will likely cause your program to
`486`		`-generate an easily diagnosed error.`
	`484`	+mistakenly write ``z =y.sort()`` thinking``z`` is a sorted copy of ``y``,
	`485`	+you'll instead end up with ``z`` being ``None``, which will likely cause
	`486`	`+your program togenerate an easily diagnosed error.`
`487`	`487`
`488`	`488`	`However, there is one class of operations where the same operation sometimes`
`489`	`489`	`has different behaviors with different types: the augmented assignment`

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