为什么我的字典值在循环后会发生变化？

Question

下面是我的python代码：

from collections import defaultdict
data = {"Manoj":{"India":{"Airtel":2000,"Vodafone":5000},"Pakistan":{"Airtel":3000}},
    "Shafiq":{"Pakistan":{"Airtel":5000,"BP":10000}},
    "Shams":{"India":{"BP":400}},
    "Govind":{"India":{"Airtel":3000,"Vodafone":2000}},
    "Zakir":{"SriLanka":{"Etisalat":7000}}
    }

print("Printing data:")
print(data)
sumOperator={}
countryCustomers = defaultdict(list)

sum=0

for name,value in data.items():
    for country,value2 in value.items():
        countryCustomers[country].append(name)
        if country not in sumOperator:
            sumOperator[country]=value2
        else:
            for operator,value3 in value2.items():
                if operator not in sumOperator[country]:
                    sumOperator[country][operator] = value3
                else:
                    sum = sumOperator[country][operator] + value3
                    sumOperator[country][operator] = sum

print("")
print("Printing sumOperator:")
print(sumOperator)
print("")
print("Priniting data:")
print(data)

Output:
Printing data:
{'Zakir': {'SriLanka': {'Etisalat': 7000}}, 'Manoj': {'Pakistan': {'Airtel':3000}, 'India': {'Vodafone': 5000, 'Airtel': 2000}}, 'Shams': {'India': {'BP': 400}}, 'Shafiq': {'Pakistan': {'BP': 10000, 'Airtel': 5000}}, 'Govind': {'India': {'Vodafone': 2000, 'Airtel': 3000}}}

Printing sumOperator:
{'Pakistan': {'BP': 10000, 'Airtel': 8000}, 'SriLanka': {'Etisalat': 7000}, 'India': {'Vodafone': 7000, 'BP': 400, 'Airtel': 5000}}

Priniting data:
{'Zakir': {'SriLanka': {'Etisalat': 7000}}, 'Manoj': {'Pakistan': {'BP': 10000, 'Airtel': 8000}, 'India': {'Vodafone': 7000, 'BP': 400, 'Airtel': 5000}}, 'Shams': {'India': {'BP': 400}}, 'Shafiq': {'Pakistan': {'BP': 10000, 'Airtel': 5000}}, 'Govind': {'India': {'Vodafone': 2000, 'Airtel': 3000}}}

为什么我的字典“数据”在初始化另一个字典后会改变值？最后一个print data语句生成另一个数据字典，它与开始初始化的数据字典不同

Answer 1

当程序将值添加到sum操作符字典时，问题就会出现，主要是循环中的最后一个else语句。您正试图从另一个字典的值构建此字典，因此有sumOperator[key] = value，其中value引用另一个字典中的项。这只是将一个字典指向另一个字典的值；底层的值不会被复制。因此，当您更新sum操作符的值时，主数据字典也得到了更新。要解决这个问题，只需在将值添加到新字典时复制它们。你知道吗

下面的代码可以工作，只要在更新sum操作符时添加copy()：

from collections import defaultdict
from copy import copy
data = {"Manoj":{"India":{"Airtel":2000,"Vodafone":5000},"Pakistan":{"Airtel":3000}},
        "Shafiq":{"Pakistan":{"Airtel":5000,"BP":10000}},
        "Shams":{"India":{"BP":400}},
        "Govind":{"India":{"Airtel":3000,"Vodafone":2000}},
        "Zakir":{"SriLanka":{"Etisalat":7000}}
        }

print("Printing data:")
print(data)

sumOperator={}
countryCustomers = defaultdict(list)

sum=0

for name,value in data.items():
    for country,value2 in value.items():
        countryCustomers[country].append(name)
        if country not in sumOperator:
            sumOperator[country] = copy(value2)
        else:
            for operator,value3 in value2.items():
                if operator not in sumOperator[country]:
                    sumOperator[country][operator] = copy(value3)
                else:
                    sum = sumOperator[country][operator] + copy(value3)
                    sumOperator[country][operator] = sum


print("Printing sumOperator:")
print(sumOperator)

print("Priniting data:")
print(data)

正如其他人所指出的，您可能希望查看assignment statements and copying上的Python文档页面。如果不希望修改原始副本，请记住何时需要创建显式副本。你知道吗