Iterate over list of dicts in order of property

This question already has an answer here:

How do I sort a list of dictionaries by values of the dictionary in Python? 17 answers

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Yes, both is possible with "key" keyword argument of function sorted(). Take a look at the snippet:

>>> l = [1, 3, 2]
>>> sorted(l)
[1, 2, 3]
>>> sorted(l, key=lambda x: x**2)
[1, 2, 3]
>>> sorted(l, key=lambda x: -x)
[3, 2, 1]

You can pass a callable as "key" keyword argument to sorted() and the callable will be used to provide a sorting key. For your first problem you could wrap transactions in sorted and pass lambda x: x['date] as a "key". For objects just change "key" to something like lambda x: x.date .

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Found it! From this answer:

for t in sorted(transactions, key=lambda k: k['date']):
    balance += t['amount']
    t['balance'] = balance

Funny how searching did not lead to that answer, but after posting it appears at the top of the sidebar!

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Careful, you have a typo in your loop (transactsion)

transactions.sort(key=lambda x:x['date'])
for t in transactions:
    balance += t['amount']
    t['balance'] = balance

This should do the trick, and this way your list remain sorted

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