为什么会出现此Python索引错误？

Question

I am getting the following index error when I use my code. This code is for a Aroon indicator which is used for technical analysis for stocks. The error message says the following. I am using Python27.

Traceback (most recent call last): File "C:\\Python\\Aroon.py", line 46, in aroon(20) File "C:\\Python\\Aroon.py", line 37, in aroon print highp[x] IndexError: index 106 is out of bounds for axis 0 with size 106

The sample data can be located at http://sentdex.com/sampleData.txt I copied this to a text file of my own. The code is below. It prints the data but then I get the following error message and i'm trying to figure out why.

import numpy as np
import time

sampleData = open("sampleData.txt", "r").read()
splitData = sampleData.split("\n")

date, closep, highp, lowp, openp, volume = np.loadtxt(splitData,delimiter=",", unpack=True)


def aroon(tf):

    AroonUp = []
    AroonDown = []
    AroonDate = []

    x = tf

    while x <= len(date):
        Aroon_Up = ((highp[x-tf:x].tolist().index(max(highp[x-tf:x])))/float(tf))*100#numpy array to list.

        Aroon_Down = ((lowp[x-tf:x].tolist().index(min(lowp[x-tf:x])))/float(tf))*100#numpy array to list.

        AroonUp.append(Aroon_Up)
        AroonDown.append(Aroon_Down)
        AroonDate.append(date[x])

        x+=1

        print "######"
        print highp[x] # THIS IS LINE 37
        print Aroon_Up
        print "=="
        print lowp[x]
        print Aroon_Down
        print "#####"
    return AroonDate,AroonUp,AroonDown


aroon(20)

Answer 1

You should change this line:

while x <= len(date):

to this:

while x < len(date):

There are 106 lines in your file, and it's looking for the 107th line (zero based).

Answer 2

请记住，在Python中，索引从0而不是1开始len(date) == 106 ，因此最大的有效索引是10 5 ，而不是106。尝试将while条件更改为

while x < len(date):

Answer 3

The Python devs has gone to great lengths to make sure that you almost never have to manually index, precisely because it us error prone.

The more Pythonic way to solve a problem where you want both the elements in a sequence, date, (which should probably be called dates btw) AND the index of these elements is to use enumerate:

for x, date in enumerate(dates):
    if x < tf:
        continue
    # more code

or as has already been suggested, to use range:

for x in range(tf, len(dates)):
    # more code

Personally I would use the enumerate.

On a side note, I recommend to use descriptive variable names, that makes it easier for others (and yourself) to read the code.

Answer 4

The problem lies with how ranges are specified in Python: highp[x-tf:x] .

The last index in this list is x-1 , but you are trying to print index x .

When specifying a range in a list, the last element is not included. See the following example in the Python shell:

>>> a=[0,1,2,3]
>>> print a[0:1]
[0]
>>> print a[0:4]
[0, 1, 2, 3]
>>> print a[3:4]
[3]
>>> print a[0:5]
[0, 1, 2, 3]
>>> print a[0:6]
[0, 1, 2, 3]
>>> print a[0]
0
>>> print a[3]
3
>>> print a[4]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range
>>> 

You will have the same problem with lowp[x-tf:x]

The second issue is that you increment x first ( x+=1 ) and then use x as an index in you print statement, you should reverse the order:

print "######"
print highp[x] # THIS IS LINE 37
print Aroon_Up
print "=="
print lowp[x]
print Aroon_Down
print "#####"

x+=1

Answer 5

you could use the for loop.See the following example in the python shell

for x in xrange(1,4): ... print x ... 1 2 3