How to print and calculate a value in Python that is inside a Json in MongoDB

Question

I have this Json inside mongodb

{
"_id" : ObjectId("5aba203f00435837802f9c49"),
"AED" : 4.572098,
"AFN" : 86.093419,
"ALL" : 130.478529,
"AMD" : 597.524404,
"ANG" : 2.216574,
"AOA" : 264.413246,
}

And this in Python

import pymongo
uri = "mongodb://127.0.0.1:27017"
client= pymongo.MongoClient(uri)
database = client['countries_db']
collection = database['currency']

currency =[AED['AED'] for AED in collection.find({})]
res=currency*2
print(res)

Output: [4.572098, 4.572098]

And when I print this, It comes as a string value, It repeats AED two times. Is there any way to call the value as float and calculate it? Thanks.

Grant David Bachman · Accepted Answer · 2018-03-28 13:33:53Z

2

The problem isn't that it's returning a string value; it's returning a list. When you try to multiply a list, it'll just duplicate itself that many times, which is what you're seeing here. How you resolve it depends on how many elements you expect to get back from the find() operation as well as what you'd like to do with them all.

If you're expecting 1 element as a result of the find() operation, you should turn that into a find_one(), which will return a float, making your multiplication operation work as expected with the following code:
```
item = collection.find_one({})  # Returns a single doc. Note the lack of square brackets
currency = item['AED']  # Get the desired key of the document
res = currency * 2
```
If you're expecting more than 1 element, you can multiple each returned value by 2 by running a map on it with res = map(lambda x: x*2, currency)

edited Mar 28, 2018 at 13:33

answered Mar 28, 2018 at 11:36

Grant David Bachman

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2 Comments

Filipe Santos Over a year ago

I just have to import one element, it didn't work, I want the element that is inside the object, do I have to import the object in Mongo?

Grant David Bachman Over a year ago

See the changes to my response. You still needed to remove the square brackets wrapping the call, which was creating a list (in addition to the call to find(), which was also returning a list).

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