Python排序词典列表

Question

I have a list of dictionaries:

AccountValues = [
{'portfolio_ref': 1, 'tag': 'FullInit', 'value': '20642.95', 'currency': 'USD', 'percent': 0.0}, 
{'portfolio_ref': 1, 'tag': 'FullMaint', 'value': '21350.54', 'currency': 'USD', 'percent': 0.0}, 
{'portfolio_ref': 1, 'tag': 'NetLiq', 'value': '70976.05', 'currency': 'USD', 'percent': 100.0} ]

Simple mission per SQL description: Order by portfolio_ref ASC, percent DESC

What I tried unsuccessfully:

sorted(AccountsValues, key=lambda x: (x[1],-x[4]))

which gives me

KeyError: 1

Second attempt:

import operator
result = sorted(myAccountsValues, key=itemgetter('percent'))

which fails to sort on percentage.

Answer 1

You can use dict.__getitem__ or its syntactic sugar [] :

res = sorted(AccountValues, key=lambda x: (x['portfolio_ref'], -x['percent']))

Remember that dictionaries are not indexable by integers. Historically (pre-3.6), they are not even ordered. Even in Python 3.7, you cannot directly extract the n th key or value.

Result:

print(res)

[{'portfolio_ref': 1, 'tag': 'NetLiq', 'value': '70976.05', 'currency': 'USD', 'percent': 100.0},
 {'portfolio_ref': 1, 'tag': 'FullInit', 'value': '20642.95', 'currency': 'USD', 'percent': 0.0},
 {'portfolio_ref': 1, 'tag': 'FullMaint', 'value': '21350.54', 'currency': 'USD', 'percent': 0.0}]

Answer 2

You just have to combine all the things you did correctly: sort keys as a tuple and the proper way of referencing a dict entry:

>>> sorted(AccountValues, key=lambda x: (x["portfolio_ref"], -x["percent"]))
[{'tag': 'NetLiq', 'portfolio_ref': 1, 'value': '70976.05', 'percent': 100.0, 'currency': 'USD'},
 {'tag': 'FullInit', 'portfolio_ref': 1, 'value': '20642.95', 'percent': 0.0, 'currency': 'USD'},
 {'tag': 'FullMaint', 'portfolio_ref': 1, 'value': '21350.54', 'percent': 0.0, 'currency': 'USD'}]

Better yet, use

sorted(AccountValues, key=itemgetter("portfolio_ref", "percent"))

Your first attempt failed because x[1] and x[4] are not valid references into the dictionaries: you have to use the labels you originally gave, not relative positions.

Your second attempt is deficient only because you don't have the secondary sort key.