如何使 for 循环保持返回值？答案

【问题标题】：How to make a for loop keep returning values?如何使 for 循环保持返回值？
【发布时间】：2019-11-23 13:38:06
【问题描述】：

我必须设置两个循环。一个保持对列表中负数的总数并返回的值。另一个将否定附加到一个单独的列表也将被返回。我只能在每个循环中返回第一个值。

# Given the parameter list, returns the count of negative numbers in the list
def num_negatives(list):
    negatives = 0
    for neg in list:
        if neg < 0:
            negatives += 1
            return negatives

# Given the parameter list, returns a list that contains only the negative numbers in the parameter list 
def negatives(list):    
    negList = []
    for negItems in list:
        if negItems < 0:
            negList.append(negItems)
            return negList    

# Prompts the user to enter a list of numbers and store them in a list
list = [float(x) for x in input('Enter some numbers separated by whitespace ').split()]
print() 

# Output the number of negatives in the list
print('The number of negatives in the list is', num_negatives(list))
print()

# output the list of negatives numbers    
print('The negatives in the list are ', end = '') 

for items in negatives(list):
    print(items, ' ', sep = '', end = '')     
print('\n')

如果我在程序开始时输入值1 2 3 4 5 -6 7 -8 9 -12.7，我应该会收到这个。

The number of negatives in the list is 3

The negatives in the list are -6.0 -8.0 -12.7

相反，我只得到：

The number of negatives in the list is 1

The negatives in the list are -6.0

【问题讨论】：

标签： python list for-loop return negative-number

【解决方案1】：

我认为您正在搜索yield，这是创建可迭代对象的优雅解决方案。

def num_negatives(list):
    negatives = 0
    for neg in list:
        if neg < 0:
            yield neg  # I return the negative number directly.

def negatives(list): 
    negList = []   
    negatives_generator = num_negatives(list)
    for negItem in negatives_generator:
        negList.append(negItem)
    return negList

最后你可以打印否定列表和len(negatives)，你现在都有了。

更多详情：What does yield do?

【讨论】：

虽然这是一个有用的工具，但它并没有解决 OP 的情况，它似乎处理的是一个需要特定方法的作业问题。

【解决方案2】：

您的退货地点有误。您不想多次返回。您只想在函数运行完成后返回最终值一次。所以你的函数应该是这样的：

# Find number of negative numbers in the list
def num_negatives(list):
    negatives = 0
    for neg in list:
        if neg < 0:
            negatives += 1
    return negatives

def negatives(list):    
    negList = []
    for negItems in list:
        if negItems < 0:
            negList.append(negItems)
    return negList

【讨论】：