调用函数时如何在函数中定义变量？

Posted 2023-03-24

【中文标题】调用函数时如何在函数中定义变量？

【英文标题】：How to define a variable in a function when calling the function?

【发布时间】：2021-12-21 20:05:37

【问题描述】：

当我运行我的代码时，我得到“NameError: name ‘mean’ is not defined”。当我尝试调用我的函数“calculateVariance(mean, nums)”时出现此错误。我似乎无法弄清楚如何在不必更改“calculateVariance(mean, nums)”函数的情况下定义“均值”.. 如果这有意义..

代码如下：

import math
import matplotlib.pyplot as plt

def readFile(file_name):

    with open('data_1.txt', 'r') as DataOne:
    nums = DataOne.read()
    
    print(nums)

    return nums

def calculateMean(nums):

    sumOfNums = 0

    for i in range(len(nums)):
        sumOfNums += i
    
    mean = sumOfNums//len(nums)

    print("The mean is : ", mean)

    return mean

def calculateVariance(mean, nums):

    squaredDifferences = 0

    for number in nums:
        difference =mean - number
        squaredDiff = difference ** 2
        squaredDifferences += squaredDiff
    variance = squaredDifferences // (len(nums)-1)

    print(" The variance is : ", variance)

    return variance

def calculateSD(variance):
 
    square_root = math.sqrt(number)
    StandDev = square_root(variance)

    print("Standard Deviation is : ", StandDev)

    return StandDev

def showHistogram(nums):

    num_bins = 10
    plt.hist(listOfNums, num_bins)
    plt.show()

nums = readFile('data_1.txt')
calculateMean(nums)
calculateVariance(mean, nums)
calculateSD(variance)
       

【问题讨论】：

请始终发布带有完整回溯的整个错误消息。您的缩进也不正确。这是复制/粘贴错误还是您的实际代码？ return 语句应该缩进，以便它们属于函数。

如果您在函数calculateMean() 中定义mean，它将仅对该函数是本地的。这意味着它不能在函数之外使用。假设缩进问题只是一个拼写错误，您应该使用来自calculateMean() 的返回值——类似于mean = calculateMean(nums)。

仅供参考，如果您使用 pandas 包，这些只是单行调用：nums.mean()、nums.var()

【参考方案1】：

当您调用返回mean 的函数时，您实际上并没有保存它。因此在调用其他函数时不能使用它。

尝试将其保存为 mean_result 或类似名称以供以后使用（避免命名冲突）。

【参考方案2】：

您应该将来自函数calculateMean(nums) 的mean 结果存储在一个变量中。您还需要为其他功能执行此操作。

import math
import matplotlib.pyplot as plt

def readFile(file_name):
    with open('data_1.txt', 'r') as DataOne:
    nums = DataOne.readlines()
    print(nums)
    return nums

def calculateMean(nums):
    sumOfNums = 0
    for i in range(len(nums)):
        sumOfNums += i
    
    mean = sumOfNums//len(nums)
    print("The mean is : ", mean)
    return mean

def calculateVariance(mean, nums):
    squaredDifferences = 0
    for number in nums:
        if number != '':
            difference = mean - int(number.replace('\n', ''))
            squaredDiff = difference ** 2
            squaredDifferences += squaredDiff
    variance = squaredDifferences // (len(nums)-1)
    print(" The variance is : ", variance)
    return variance

def calculateSD(variance):
    square_root = math.sqrt(number)
    StandDev = math.sqrt(variance)
    print("Standard Deviation is : ", StandDev)

    return StandDev

def showHistogram(nums):
    num_bins = 10
    plt.hist(listOfNums, num_bins)
    plt.show()

nums = readFile('data_1.txt')
mean = calculateMean(nums)
variance = calculateVariance(mean, nums)
stdev = calculateSD(variance)

【讨论】：

当我这样做时，我在 方差 = calculateVariance(mean_result, nums) 文件“N:\Fall 2021\DataScience Intro to Python\Lab 12\SDandHistogram.py”，第 45 行，在 calculateVariance 差异 = mean_result - number TypeError: unsupported operand type(s) for - : 'int' 和 'str'" 有什么办法可以解决这个问题吗？当我尝试执行 int(number) 时，它给了我另一个错误，提示“invalid literal for int() with base 10: '\n'”

抱歉，我之前的评论不允许我编辑

尝试将mean - number更改为mean - int(number.replace('\n', ''))

txt阅读器的每一行似乎都有换行符或\n

当我这样做时，我得到“文件“N:\Fall 2021\DataScience Intro to Python\Lab 12\SDandHistogram.py”，第 37 行，在 calculateVariance 差异 = mean - int(numbers.replace ('\n', '')) ValueError: int() 基数为 10 的无效文字：'' "