Appending JSON data from one file to another in Python

Question

Consider this code, which is understandably failing:

def testDataTransform():
    source = 'data/threads/testFile2.json' 
    newFile = 'data/threads/testFile1.json'

    jX = returnJson(source)
    jY = returnJson(newFile)

    for dataL1 in jX:
        #print dataL1['city']
        for dataL2 in jY:
            if dataL1['city'] == dataL2['city']:
                dataL2.append(dataL1['population']) 

    print dataL2


# end testDataTransform

def returnJson(source):
    #Grab destination file json
    try:
       with open(source) as jsonFile: # Open and verify file is there
        # load JSON object into memory
        j = json.load(jsonFile)

        return j
    except Exception, e:
        print e
        raise
# end returnJson

testDataTransform()

The error generated is: AttributeError: 'dict' object has no attribute 'append', which I now understand is due to trying to use append on a file steam and thus appending my JSON incorrectly. The question is how would I do this correctly? I want to add population data, which is in the source file.

JSON structure in testFiles look like this:

[

    {
        "city": "New York",
        "lat": 20.1234,
        "long": 32.09876
    },
    {
        "city": "London",
        "lat": 21.1234,
        "long": 37.09876
    },
    {
        "city": "New Jersey",
        "lat": 10.1234,
        "long": 30.09876
    }

]

One has a "population" node and other does not. I want to copy that population data from one file to another. How is that done? I wonder if converting the file stream into an array would help, but how do I even do that?

Thanks.

kdopen · Accepted Answer · 2014-12-11 19:46:56Z

1

The error message is telling you exactly what's wrong. It's in this line

dataL2.append(dataL1['population'])

dataL2 is a dict(), and dict() does not have a method called append

What you want is

dataL2["population"] = dataL1['population']

Basically, the call to json.load() for this file returns a list of dicts(). JSON arrays map to Python lists, JSON objects map to Python dictionaries. To add a new key to a dict, simply set a value on it.

answered Dec 11, 2014 at 19:46

kdopen

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3 Comments

Mr. Concolato Over a year ago

Well look at that! Nice. But now the values are all the same for every object

kdopen Over a year ago

Didn't say that was your only problem :) What's the contents of the other test file?

kdopen Over a year ago

check the indentation in your modified code. Is the assignment only happening when the if condition is met?

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