[0] * x语法在Python中做什么? [英] What does the [0]*x syntax do in Python?

问题描述

一个简短的问题，我正在看下面的代码

A flash question, I'm looking at the following code

from __future__ import division
import math
import time

def dft(x, inverse = False, verbose = False) :
    t = time.clock()
    N = len(x)
    inv = -1 if not inverse else 1
    X =[0] * N
    for k in xrange(N) :
        for n in xrange(N) :
            X[k] += x[n] * math.e**(inv * 2j * math.pi * k * n / N)
        if inverse :
            X[k] /= N
    t = time.clock() - t
    if verbose :
        print "Computed","an inverse" if inverse else "a","DFT of size",N,
        print "in",t,"sec."
    return X

我想知道(我不知道python):

and I'm wondering (I do not know python):

• X = [0] * N行做什么?
• 为什么双星号**?

推荐答案

此处演示了x = [0] * n:

>>> [0]*10
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

它相乘"列表元素

>>> [1, 2, 3] * 3
[1, 2, 3, 1, 2, 3, 1, 2, 3]

**是电源操作员

>>> 3**2
9

尽管要小心，但也可能是**(在不同的上下文中)，请在此处查看有关此内容的更多信息

Although be careful, it can also be **kwargs (in a different context), see more about that here Proper way to use **kwargs in Python

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