IndexError: list index out of range

Question

#coding:utf-8 -*-
#! /user/bin/env/python

python vectorsum.py 1000

import sys
import numpy as np
from datetime import datetime
"""input format�� python vectorsum.py n
n: the expected size for the vector"""

def pythonSum(n):
a = range(n)
b = range(n)
c = []
for i in range(n):
a[i] = i ** 2
b[i] = i ** 3
c.append(a[i]+b[i])
return c

def numpysum(n):
a = np.arange(n) ** 2
b = np.arange(n) ** 3
c = a + b
return c

size = int(sys.argv[1])

start = datetime.now()
c = pythonSum(size)
delta = datetime.now() - start
print ("The last 2 elements of the sum", c[-2:])
print ("pythonSum elspaed time in microseconds", delta.microseconds)
start = datetime.now()
c = numpysum(size)
delta = datetime.now() - start
print ("The last 2 elements of the sum", c[-2:])
print ("numpysum elspaed time in microseconds", delta.microseconds)

运行结果：Traceback (most recent call last):
File "D:\workspace\PythonLearn1\src\NumpyLearn__init__.py", line 26, in
size = int(sys.argv[1])
IndexError: list index out of range

我用的是Eclipse下的 python,请问这个越界了，应该在哪里输入 python vectorsum.py n,各位大神，帮忙解决一下吧

Answer 1

这个问题一般是索引越界了，这有两种情况，一种是list[index]index超出范围，另一种就是你的list是一个空的 没有一个元素。
而一般都要事先判断一下，随便返回什么，只要判断跳过会报错的逻辑就好了，就比如c[-2:]那一块，

而你的问题是第二种，sys.argv[1] 表示取命令行的第一个参数，但是你在调用vectorsum.py的时候没有加任何参数，所以数组当然就越界了，你的n没有取任何值