JSON:TypeError:Decimal('34 .3')不可序列化JSON [英] JSON: TypeError: Decimal('34.3') is not JSON serializable

问题描述

我正在运行一个SQL查询，该查询返回一个十进制列表.当我尝试将其转换为JSON时，出现类型错误.

I am running an SQL query which returns a list of Decimals. When I try to convert this into JSON i get the type error.

查询:

res = db.execute("""
SELECT CAST ((SUM(r.SalesVolume)/1000.0) AS decimal(6,1))
FROM RawData r
INNER JOIN Product p
ON r.ProductId = p.ProductId 
INNER JOIN Calendar c
ON r.DayId = c.DayId
WHERE c.WeekCodeInYear BETWEEN 1 AND 12
AND 
c.YearId = 2014
GROUP BY c.WeekCodeInYear """)

结果列表:

[Decimal('34.3'), Decimal('50.9'), Decimal('31.5'), Decimal('23.3'), Decimal('19
.7'), Decimal('56.9'), Decimal('43.8'), Decimal('35.2'), Decimal('29.2'), Decima
l('43.7'), Decimal('42.6'), Decimal('23.4')]

代码:

for row in res:
    testlist.append (row[0])
    print testlist

list = json.dumps(testlist)

然后我得到了Unable to serialize error 尝试在线查找，没有太大帮助. 请注意，最终列表将作为输入数据进入图表.

And the I get the Unable to serialize error Tried looking up online, no much help. Please note that the final list would go as input data to a chart.

推荐答案

如错误所示，Decimal类型不能直接序列化为JSON.如果希望将Decimal转换为float，可以考虑将其转换为float，但是可能会舍入错误.即

As the error says, the Decimal type is not able to be serialized directly into JSON. Considering casting the Decimal into a float if you wish to keep that as a number, however you may get rounding errors. i.e.

for row in res:
    testlist.append(float(row[0]))

或者使用列表理解来构建列表，这一次我转换为str.

Or alternatively build the list using list comprehension, this time I cast to str.

testlist = [str(row[0]) for row in res]

后者是适当的表示形式，因为Decimal类型可以由str明确表示.您可以像这样抓住原始值

The latter is an appropriate representation as the Decimal type can be unambiguously represented by str. You can grab the original value like so

from decimal import Decimal
jlist = json.dumps(testlist)  # don't use list as it's predefined type
new_list = json.loads(jlist)
new_dlist = [Decimal(s) for s in new_list]

new_dlist应该与原始的templist相同.

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