Python：是否有一个与.index（）类似但相反的内置函数？ [英] Python: Is There a builtin that works similar but opposite to .index()?

问题描述

只是一个警告：我最近才开始编程，而Python是到目前为止我的第一门语言，也是唯一的语言。

Just a forewarning: I just recently started programming and Python is my first language and only language so far.

是否有一个内置的内建函数与 .index（）？我正在寻找它是因为我做了一个布尔函数，其中有一个整数列表，并且如果给定的整数列表是幂的列表，我想返回 True 某些形式为 [x ^ 0，x ^ 1，x ^ 2，x ^ 3，...] 的int，否则为False。

Is there a builtin that works in the opposite way of .index()? I'm looking for this because I made a bool function where I have a list of ints and I want to return True if the given list of ints is a list of powers of some int x of the form [x^0, x^1, x^2, x^3, ...] and `False' otherwise.

我想在代码中说的是：

n >= 1  
while the position(n+1) = position(1)*position(n) 
    for the length of the list
    return True
otherwise 
    False.

是否有内置函数可以输入位置并返回列表中的项目？

Is there a builtin I could use to input the position and return the item in the list?

list = [1,2,4,8,16]
position(4)

返回整数16。

编辑：抱歉，我不知道如何在这里格式化
好​​，请显示我的意思：

sorry I don't know how to format on here ok ill show what I mean:

def powers(base):
''' (list of str) -> bool
Return True if the given list of ints is a list of powers of 
some int x of the form [x^0, x^1, x^2, x^3, ...] and False 
otherwise.
>>> powers([1, 2, 4, 8]) 
True
>>> powers([1, 5, 25, 75])
False
'''

最终编辑：

我刚刚从这里浏览了所有可用的列表方法（ https://docs.python.org/2/tutorial/datastructures.html ），然后阅读说明。我要的东西不能作为列表方法使用：（

I just went through all of the available list methods from here (https://docs.python.org/2/tutorial/datastructures.html) and read the descriptions. What I'm asking for, isn't available as a list method :(

抱歉给您带来的不便。

推荐答案

作为对以下内容的解答：

As an answer to:

是否有内置函数可以用来输入头寸并返回列表中的项目？

Is there a builtin I could use to input the position and return the item in the list?

您只需要访问列表其索引为：

You just need to access the list with it's index as:

>>> my_list = [1,2,4,8,16]
>>> my_list[4]
16  # returns element at 4th index

而且，此属性与语言无关，所有语言均支持。

And, this property is independent of language. All the languages supports this.

根据您在问题，您可以将函数编写为：

Based on your edit in the question, you may write your function as:

def check_value(my_list):
    # if len is less than 2
    if len(my_list) < 2:
        if my_list and my_list[0] == 1:
            return True
        else:
            return False 
    base_val = my_list[1] # as per the logic, it should be original number i.e num**1 
    for p, item in enumerate(my_list):
        if item != base_val ** p: 
            return False
    else:
        return True

示例运行：

>>> check_value([1, 2, 4, 8])
True
>>> check_value([1, 2, 4, 9])
False
>>> check_value([1, 5, 25, 75])
False

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