More reliable method to get specific JSON value using Python

Question

Based on this Q&A a certain JSON value can be found using print data[u'X'][50][u'Z']

data[u'X'] results in:

{
  "X" : [ {
    "A" : "B",
    ...
  }, {
    ...
  }, {
    "C" : "D",
  } ]
}

Applying the integer method means that every part that is separated by a comma, e.g. "element" : [ { "name" : "value", ... }, needs to be counted until the required piece has been found, in this case number 50.

What if the JSON structure will be changed in the future? Does this mean that the integer should be updated every time?

In my opinion this method is fragile. How to make it more reliable?

Attempts

print data[u'X'][0] results in:

{u'A': u'B', u'C': u'D'}

while

print data[u'X'][u'A']

results in:

Traceback (most recent call last):
  File "test.py", line 9, in <module>
    print data[u'beans'][u'modelerType']
TypeError: list indices must be integers, not unicode

Based on your sample, print data[u'X'][50][u'Z'] will be a KeyError. What is "the integer method" to which you refer? Do you mean indexing into a list (in which case, it certainly does not need "to be counted until the required piece has been found" - indexing is O(1))? — jonrsharpe
– jonrsharpe, Commented Jan 26, 2015 at 17:30
Yes, if you structure changes, your hard-coded path into that structure likely has to change too. You have a route through a structure, so if the structure changes, your route has to change accordingly. You usually don't hardcode the route; you usually pick landmarks instead, but your question is too broad and devoid of detail to give you suitable landmarks to traverse by. — Martijn Pieters
– Martijn Pieters, Commented Jan 26, 2015 at 17:37

Wolph · Accepted Answer · 2015-01-26 17:34:16Z

2

There are 2 types of collections in JSON, arrays and objects (see the API for more info)

For example, a list of items:

x = ['a', 'b', 'c', 'd']
x[2] // Returns 'c'

And an object:

x = {"a": 10, "b": 20, "c": 30}
x['b'] // Returns 20

So assuming you use an object to store the data than you won't need an index number at all, just the name of the property. If you use the list, than you will have to store the list index.

It is possible to store an array in an object and vice versa. For example:

x = [1, 2, 3, {"a": 10, "b": 20, "c": [30, 40, 50]}]
x[0] // Returns 1
x[3] // Returns {"a": 10, "b": 20, "c": [30, 40, 50]}
x[3]['a'] // Returns 10
x[3]['c'][2] // Returns 50

answered Jan 26, 2015 at 17:34

Wolph

80.4k12 gold badges142 silver badges152 bronze badges

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

9 Comments

030 Over a year ago

When strings are used it results in TypeError: list indices must be integers, not unicode

Wolph Over a year ago

@utrecht: note the difference between { and [. With an object (where you can use strings/unicode) you have to use {. With an array you have to use numbers as indices. Within python it's the difference between a list() and a dict() which are also denounced by a [] and {} respectively.

030 Over a year ago

So in this case integers should be used always? It is not possible to make it less fragile by using strings?

Wolph Over a year ago

If you want to use strings, use objects. If you have no need for strings, use an array. Note that the downside of objects is the inconsistent sort order, so if you need ordering you will have to use an array.

030 Over a year ago

I cannot change the json file. I am trying to get specific value from a jmx page.

|

user4678636 · Accepted Answer · 2015-03-17 00:44:28Z

0

This is probably closer to what you're looking for:

models = ['JvmMetrics', 'MyMetrics']
filtered = filter(ldata['beans'], lambda x: x['modelerType'] in models)

It's unlikely that there's a better way unless you want to build another dict from the JMX response.

answered Mar 17, 2015 at 0:44

user4678636

1

Collectives™ on Stack Overflow

More reliable method to get specific JSON value using Python

2 Answers 2

9 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

9 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related