How to have a json path returned, given a string?

Question

I'm facing a problem here, because I must receive a json which contains a string with the path of some data in another json.

the Json which contains some data

json1 = {
    "Items": [{
                  "building": "buildingA",
                  "y": [1, 2, 3],
                  "yl": "A,B,C",
                  "xl": "Data",
                  "x": [1, 2, 3]
              },
              {
                  "y": [4, 5, 6],
                  "x": [1, 2, 3],
                  "predio": "BuildingB",
                  "yl": "D,E,F",
                  "xl": "Data"
              }]
}

and the json that contains the path of the desired value:
```
json2 = {
    "y": "y//1",
}
```

I tried to make this code to solve the problem:

def size2(a,i):
 x=a.split('//')
 y=len(x)
 if y ==1:
    return i[x[0]]
 elif y==2:
    return i[x[0]][x[1]]
 elif y==3:
    return i[x[0]][x[1]][x[2]]

y=json2['y']
for i in json1['Items']:
 print(i['y'][1])        #this way works
 print(size2(y,i))       #this way fails

The error message is:

TypeERROR: list indices must be integers, not str

Does anyone know how to solve this problem?

Non-sarcastic actual help: when you do the list access it returns the member in the JSON data which is a string, which you are then trying to use for a subsequent index access, which is throwing the error. Cast the result to an int: int(x[1]). — Jared Smith
– Jared Smith, Commented May 30, 2017 at 0:01

martineau · Accepted Answer · 2017-05-30 04:02:05Z

2

You could do it this way which assumes that any path component comprised of all digit characters is a integer sequence index:

def size2(y, i):
     obj = i
     for comp in ((int(z) if z.isdigit() else z) for z in y.split('//')):
        obj = obj[comp]
     return obj

y = json2['y']
for i in json1['Items']:
    print(size2(y, i))  # this way now works

The size2() function could be made even more succinct by using the built-in reduce() function:

def size2(y, i):
    return reduce(lambda obj, v: obj[int(v) if v.isdigit() else v], y.split('//'), i)

edited May 30, 2017 at 4:02

answered May 30, 2017 at 3:13

martineau

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2 Comments

MSeifert Over a year ago

Yes, I also considered something like that. It will work as long as there are no string-digit-dict-keys. :)

martineau Over a year ago

@MSeifert: True. It's difficult to tell which of our answers would be more appropriate from the minimal information in the question. Your approach is probably more "Pythonic" in the sense that it uses EAFP instead of LBYL the way mine does.

MSeifert · Accepted Answer · 2017-05-30 00:34:10Z

2

As already pointed out in the comments, simply convert indices to integers before you index a sequence:

def size2(a,i):
    x = a.split('//')
    obj = i
    for part in x:  # using a loop you don't need to special case based on the length
        try:
            # Try to get it without converting to integer, for example to access dictionaries
            obj = obj[part]
        except TypeError:
            # Fallback to integer indexing
            obj = obj[int(part)]
    return obj

answered May 30, 2017 at 0:34

MSeifert

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