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Python 3.5 random.shuffle problem

世界只因有你 2017-05-18 10:48:52

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When generating a random list, the random.shuffle() function is used. The following questions arise about the call of this function:
If a list is explicitly defined, such as li = [], the shuffle function It can produce the desired results;
But if list(range(n)) is used as the parameter of shuffle, None will be returned. As shown in the figure:

What's going on? They all belong to the list category

世界只因有你

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黄舟2017-05-18 10:50:52 2 floor

>>> help(random.shuffle) Help on method shuffle in module random: shuffle(x, random=None) method of random.Random instance Shuffle list x in place, and return None. Optional argument random is a 0-argument function returning a random float in [0.0, 1.0); if it is the default None, the standard random.random will be used.

It is mentioned in the document that if anlist对象, 则直接作用鱼listobject

is given

>>> a = list(range(20)) >>> a [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] >>> random.shuffle(a) >>> a # a的值已改变 [1, 6, 3, 15, 0, 5, 19, 10, 7, 18, 4, 2, 12, 14, 8, 16, 9, 11, 13, 17] >>>

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Peter_Zhu2017-05-18 10:50:52 1 floor

Becauserandom.shuffle()会直接作用于list本身，而不会返回任何值，所以你第一个语句的结果会是None.但是在random.shuffle(li)的时候，你打印的是lithis list itself has been changed. If you write like this