Python JSON: TypeError: Decimal('34.3') 不是 JSON 可序列化的
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JSON: TypeError: Decimal('34.3') is not JSON serializable
提问by Tauseef Hussain
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.
我正在运行一个 SQL 查询，它返回一个小数列表。当我尝试将其转换为 JSON 时，出现类型错误。
The query:
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 """)
Result List:
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')]
Code:
代码：
for row in res:
testlist.append (row[0])
print testlist
list = json.dumps(testlist)
And the I get the Unable to serialize errorTried looking up online, no much help.
Please note that the final list would go as input data to a chart.
我得到了Unable to serialize error尝试在线查找，没有太大帮助。请注意，最终列表将作为图表的输入数据。
采纳答案by metatoaster
As the error says, the Decimaltype is not able to be serialized directly into JSON. Considering casting the Decimalinto a floatif you wish to keep that as a number, however you may get rounding errors. i.e.
正如错误所说，该Decimal类型无法直接序列化为 JSON。如果您希望将其保留为数字，请考虑将其Decimal转换float为 a，但是您可能会遇到舍入错误。IE
for row in res:
testlist.append(float(row[0]))
Or alternatively build the list using list comprehension, this time I cast to str.
或者，或者使用列表理解构建列表，这次我转换为str.
testlist = [str(row[0]) for row in res]
The latter is an appropriate representation as the Decimaltype can be unambiguously represented by str. You can grab the original value like so
后者是一种适当的表示，因为该Decimal类型可以由 明确表示str。您可以像这样获取原始值
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_dlistshould be identical to the original templist.
new_dlist应该和原来的一样templist。
回答by LittleQ
Use a override default:
使用覆盖default：
import json
from decimal import Decimal
def default(obj):
if isinstance(obj, Decimal):
return str(obj)
raise TypeError("Object of type '%s' is not JSON serializable" % type(obj).__name__)
json.dumps(testlist, default=default)
Or just do stron Decimalobject:
或者只是str在Decimal对象上做：
for row in res:
testlist.append (str(row[0]))
json.dumps(testlist)
