Python中Max()函数获取XML数据返回错误值的排查求助

问题描述 #

需求为找出2019年4月期间，分发食物磅数最多、服务个人数量最多、服务家庭数量最多的地区，但运行代码后，max函数返回的服务个人数和家庭数均为999，与XML中的实际更高数值不符。原代码如下：

import requests
from lxml import objectify

URL = 'https://data.virginia.gov/api/views/xvir-sctz/rows.xml?accessType=DOWNLOAD'
response = requests.get(URL).content

import requests
from lxml import objectify

#parse xml file
root = objectify.fromstring(response)

#print data
print(response)

#create emtpy lists to store wanted data
localities = []
pounds_of_food_distributed = []
individuals_served = []
households_served = []

#assign data values to varibles
localities = root.xpath('//response/row/row/locality/text()')
pounds_of_food_distributed = root.xpath('//response/row/row/pounds_of_food_distributed/text()')
individuals_served = root.xpath('//response/row/row/individuals_served/text()')
households_served = root.xpath('//response/row/row/households_served/text()')

#for loop to iterate through data set
for row in root.iterchildren():
    if row.get("month") == ("April") and row.get("Year") == "2019":
        localities.append(row.get("Locality"))
        pounds_of_food_distributed.append(row.get("Pounds"))
        individuals_served.append(row.get("Individuals"))
        households_served.append(row.get("Households"))
  
      
#Indexing to retrieve max value of each requested variable    
max_pounds_index = pounds_of_food_distributed.index(max(pounds_of_food_distributed))
max_individuals_index = individuals_served.index(max(individuals_served))
max_households_index = households_served.index(max(households_served))

#print values
print("Locality with greatest distribution of food in pounds: ", localities[max_pounds_index])
print("Greatest number of individuals served: ", individuals_served[max_individuals_index])
print("Greatest number of households served: ", households_served[max_households_index])

运行结果：

Locality with greatest distribution of food in pounds:  Colonial Heights City
Greatest number of individuals served:  999.0
Greatest number of households served:  999.0

错误原因分析 #

1. 重复导入模块：代码冗余导入requests和lxml.objectify，虽不影响结果但不符合规范。
2. 全量数据与筛选数据混合：先通过XPath加载所有时间段的全量数据到列表，后续又尝试追加筛选数据，导致列表包含无关数据，干扰最大值计算。
3. 节点遍历错误：root.iterchildren()遍历的是根节点的直接子节点（外层<row>），但实际数据存储在**内层<row>**节点中，导致筛选条件失效，追加的筛选数据为空。
4. 数据类型不匹配：XPath获取的text()结果是字符串类型，max()函数按字符串字典序比较（如"999"的ASCII码大于"1000"的首字符"1"），而非数值大小，导致错误的最大值。
5. 属性名不匹配：循环中使用的"Locality"、"Pounds"等属性名，与XML实际的locality、pounds_of_food_distributed属性名不一致，无法获取正确数据。

修正后的代码 #

import requests
from lxml import objectify

URL = 'https://data.virginia.gov/api/views/xvir-sctz/rows.xml?accessType=DOWNLOAD'
response = requests.get(URL).content

# 解析XML
root = objectify.fromstring(response)

# 初始化空列表，仅存储2019年4月的数据
localities = []
pounds = []
individuals = []
households = []

# 遍历所有内层数据行
for row in root.xpath('//response/row/row'):
    # 匹配2019年4月的数据（严格对应XML属性名）
    if row.get('month') == 'April' and row.get('year') == '2019':
        localities.append(row.get('locality'))
        # 转换数值类型并处理异常值
        pounds_val = row.get('pounds_of_food_distributed')
        pounds.append(int(pounds_val) if pounds_val.isdigit() else 0)
        
        indiv_val = row.get('individuals_served')
        individuals.append(int(indiv_val) if indiv_val.isdigit() else 0)
        
        house_val = row.get('households_served')
        households.append(int(house_val) if house_val.isdigit() else 0)

# 计算最大值索引
max_pounds_idx = pounds.index(max(pounds))
max_indiv_idx = individuals.index(max(individuals))
max_house_idx = households.index(max(households))

# 输出结果
print(f"2019年4月分发食物磅数最多的地区: {localities[max_pounds_idx]}，磅数: {pounds[max_pounds_idx]}")
print(f"2019年4月服务个人数量最多的地区: {localities[max_indiv_idx]}，人数: {individuals[max_indiv_idx]}")
print(f"2019年4月服务家庭数量最多的地区: {localities[max_house_idx]}，家庭数: {households[max_house_idx]}")

关键修正点说明 #

• 移除重复导入，精简代码结构。
• 直接遍历内层<row>节点，确保正确获取数据属性。
• 严格匹配XML中的属性名（如month、year），避免数据获取失败。
• 将数值型数据转换为整数，确保max()函数按数值大小比较。
• 添加简单异常处理，避免非数值数据导致程序报错。

内容的提问来源于stack exchange，提问作者Frost4820