Append values to a list of json objects

Question

I'm collecting weather data and trying to create a list that has the latest (temperature) value by minute.

I want to add them to a list, and if the list does not contains the "minute index" it should at it as a new element in the list. So the list always keeps the latest temperature value per minute:

def AddValue(arr, value):
    timestamp = datetime.datetime.utcnow().strftime("%Y-%m-%d %H:%M")

    for v in arr['values']:
        try:
            e = v[timestamp]     # will trigger the try/catch if not there
            v[timestamp] = value
        except KeyError:
            v.append({ timestamp: value })

history = [
    { 'values': [ {'2017-12-22 10:20': 1}, {'2017-12-22 10:21': 2}, {'2017-12-22 10:22': 3} ] },
]

AddValue(history, 99)

However, I'm getting

AttributeError: 'dict' object has no attribute 'append'**

What's the point of a dictionary if you have to iterate over it? Also, you're creating a timestamp on the fly. What are the odds that the Key already exists? — cs95
– cs95, Commented Dec 22, 2017 at 10:51
I don't get why you want to trigger the except if the key is not there. — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Dec 22, 2017 at 10:53
for v in arr['values']: don't think it works because your history is list.. — Shiva
– Shiva, Commented Dec 22, 2017 at 10:56

willeM_ Van Onsem · Accepted Answer · 2017-12-22 10:57:38Z

2

You associate a key k with a value v in a dictionary d with:

d[k] = v

this works regardless whether there is already a key k present in the dictioanry. In case that happens, the value is "overwritten". We can thus rewrite the for loop to:

for v in arr['values']:
    v[timestamp] = value

In case you want to update a dictionary with several keys, you can use .update and pass a dictionary object, or named parameters as keys (and the corresponding values as value). So we can write it as:

for v in arr['values']:
    v.update({timestamp: value})

which is semantically the same, but will require more computational effort.

Nevertheless since you need to iterate over a dictionary, you perhaps should reconsider the way you structured the data.

answered Dec 22, 2017 at 10:57

willeM_ Van Onsem

482k33 gold badges483 silver badges624 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Append values to a list of json objects

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related