TypeError:列表索引必须是整数，而不是浮点数 [英] TypeError: list indices must be integers, not float

问题描述

我有一个产生错误的python 3.x程序:

I have a python 3.x program that is producing an error:

def main():
    names = ['Ava Fischer', 'Bob White', 'Chris Rich', 'Danielle Porter',
             'Gordon Pike', 'Hannah Beauregard', 'Matt Hoyle',
             'Ross Harrison', 'Sasha Ricci', 'Xavier Adams']

    entered = input('Enter the name of whom you would you like to search for:')
    binary_search(names, entered)

    if position == -1:
        print("Sorry the name entered is not part of the list.")
    else:
        print(entered, " is part of the list and is number ", position, " on the list.")
    input('Press<enter>')

def binary_search(names, entered):
    first = 0
    last = len(names) - 1
    position = -1
    found = False

    while not found and first <= last:
        middle = (first + last) / 2

        if names[middle] == entered:
            found = True
            position = middle
        elif names[middle] > entered:
            last = middle - 1
        else:
            first = middle + 1

    return position

main()

错误是:

TypeError: list indices must be integers, not float

我无法理解此错误消息的含义.

I am having trouble understanding what this error message means.

推荐答案

您似乎正在使用Python3.x. Python 3.x的重要区别之一是处理分割的方式.当您执行x / y时，在Python 2.x中将返回一个整数，因为十进制会被截断(底数除法).但是在3.x中，/运算符执行'true'除法，结果是float而不是整数(例如1 / 2 = 0.5).这意味着您现在正在尝试使用浮点数来引用列表中的位置(例如my_list[0.5]甚至my_list[1.0])，这将无法正常工作，因为Python需要一个整数.因此，您可能首先要尝试使用middle = (first + last) // 2进行调整，以使结果返回您期望的结果. //表示Python 3.x中的楼层划分.

It looks like you are using Python 3.x. One of the important differences in Python 3.x is the way division is handled. When you do x / y, an integer is returned in Python 2.x because the decimal is truncated (floor division). However in 3.x, the / operator performs 'true' division, resulting in a float instead of an integer (e.g. 1 / 2 = 0.5). What this means is that your are now trying to use a float to reference a position in a list (e.g. my_list[0.5] or even my_list[1.0]), which will not work as Python is expecting an integer. Therefore you may first want to try using middle = (first + last) // 2, adjusting so that the result returns what you expect. The // indicates floor division in Python 3.x.

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