We Keep Coding

Fetch a list from a dictionary based on a nested value?

Lets say I have a dictionary:
episode = {
"translations": [{
"language": {
"code": "de"
},
"title": "German"
}, {
"language": {
"code": "en"
},
"title": "English"
}, {
"language": {
"code": "fr"
},
"title": "French"
}]
};
I would like to get specifically the list that matches a specific language code. I could walk through the entire dictionary using the following code:
for translation in episode['translations']:
if translation['language']['code'] == 'fr':
language = translation;
break;
But that seems a bit excessive, and a waste of resources. Is there a better way of doing this, without having to walk through the entire array?

If the data is stored in a list, then the only way to extract queries based on a condition is to iterate over the entries. In the snippet you provide, the implicit assumption of using break is that there is a unique entry of interest (or perhaps the first match is of interest).
For more optimal queries of this data, it should be transformed to a different structure. For example, it's possible to convert it to a pandas dataframe or convert the data to a dictionary where keys are translation['language']['code'] (so look-ups become O(1)).

Short of modifying how you structured your data*, I don't see a way that doesn't involve traversing the whole dictionary. That being said, there are a few more elegant ways to do it, although elegance is highly subjective:
filter(lambda x: 'fr' in x['language'].values(), episode['translations'])
would give you an iterable that contains all the the entries in your dictionary that have the required language code. Calling next on it would give you the first one, for instance.
Edit:
* what SultanOrazbayev proposed in their answer is one such way to modify your data structure.

A list comprehension is neater although not really different from the original code except that it allows for more than one dictionary entry having a particular code. For example:
episode = {
"translations": [{
"language": {
"code": "de"
},
"title": "German"
}, {
"language": {
"code": "en"
},
"title": "English"
}, {
"language": {
"code": "fr"
},
"title": "French"
}]
}
list_ = [d for d in episode['translations'] if d['language']['code'] == 'en']
print(list_)
Output:
[{'language': {'code': 'en'}, 'title': 'English'}]

How to populate optional fields in a dictionary comprehension?

I'm working on some code that processes a json database with very detailed information into a simpler format. It copies some of the fields and reserializes others into a new json file.
I'm currently using a dictionary comprehension like this MVCE:
converted_data = {
raw_item['name']: {
'state': raw_item['field_a'],
'variations': [variant for variant in raw_item['field_b']['variations']]
} for raw_item in json.loads(my_file.read())
}
An example file (not the actual data being used) is this:
[
{
"name": "Object A",
"field_a": "foo",
"field_b": {
"bar": "baz",
"variants": [
"foo",
"bar",
"baz"
]
}
},
{
"name": "Object B",
"field_a": "foo",
"field_b": {
"bar": "baz",
}
}
]
The challenge is that not all items contain variations. I see two potential solutions:
Use an if statement to conditionally apply the variations field into the dictionary.
Include an empty variations field for all items and fill it if the raw item contains variations.
I'll probably settle on the 2nd solution. However, is there a way to conditionally include a particular field within a dictionary comprehension?
Edit: In other words, is approach 1 possible inside a dictionary comprehension?
An example of the desired output (using a dictionary comprehension) would be as follows:
{
"Object A": {
"state": "foo",
"variants": ["foo", "bar", "baz"]
},
"Object B": {
"state": "foo"
}
}
I've found some other questions that change the entries conditionally or filter the entries, but these don't unconditionally create an item where a particular field (in the item) is conditionally absent.

I'm not sure you realise you can use the if inside an assignment, which seems like a very clean way to solve it to me:
converted_data = {
raw_item['name']: {
'state': raw_item['field_a'],
'variants': [] if 'variants' not in raw_item['field_b'] else
[str(variant) for variant in raw_item['field_b']['variants']]
} for raw_item in example
}
(Note: using str() instead of undefined function that was given in initial example)
After clarification of the question, here's an alternate solution that adds a different dictionary (missing the empty 'variations' key if there is none:
converted_data = {
raw_item['name']: {
'state': raw_item['field_a'],
'variants': [str(variant) for variant in raw_item['field_b']['variants']]
} if 'variants' in raw_item['field_b'] else {
'state': raw_item['field_a'],
} for raw_item in example
}
If the question actually is: can a key/value pair in a dictionary literal be optional (which would solve your problem) then the answer is simply "no". But the above achieves the same for this simple example.
If the real life situation is more complicated, simply construct the dictionary as in the first solution given here and then use del(dictionary['key']) to remove any added keys that have a None or [] value after construction.
For example, after the first example, converted_data could be cleaned up with:
for item in converted_data.values:
if not item['variants']:
del(item['variants'])

You could pass the process out to a function?
def check_age(age):
return age >= 18
my_dic = {
"age": 25,
"allowed_to_drink": check_age(25)
}
You end up with the value as the result of the function call
{'age': 25, 'allowed_to_drink': True}
How you would implement this I don't know, but some food for thought.

Python - convert JSON object to dict

I am wondering how I can convert a json list to a dictionary using the two values of the JSON objects as the key/value pair.
The JSON looks like this:
"test": [
{
"name": "default",
"range": "100-1000"
},
{
"name": "bigger",
"range": "1000-10000"
}
]
I basically want the dictionary to use the name as the key and the range as the value. SO the dictionary in this case would be {default:100-1000} {bigger: 1000-10000}
Is that possible?

You can first load the JSON string into a dictionary with json.loads. Next you can use dictionary comprehension to post process it:
from json import loads
{ d['name'] : d['range'] for d in loads(json_string)['test'] }
We then obtain:
>>> { d['name'] : d['range'] for d in loads(json_string)['test'] }
{'bigger': '1000-10000', 'default': '100-1000'}
In case there are two sub-dictionaries with the same name, then the last one will be stored in the result.

Python - Searching JSON

I have JSON output as follows:
{
"service": [{
"name": ["Production"],
"id": ["256212"]
}, {
"name": ["Non-Production"],
"id": ["256213"]
}]
}
I wish to find all ID's where the pair contains "Non-Production" as a name.
I was thinking along the lines of running a loop to check, something like this:
data = json.load(urllib2.urlopen(URL))
for key, value in data.iteritems():
if "Non-Production" in key[value]: print key[value]
However, I can't seem to get the name and ID from the "service" tree, it returns:
if "Non-Production" in key[value]: print key[value]
TypeError: string indices must be integers
Assumptions:
The JSON is in a fixed format, this can't be changed
I do not have root access, and unable to install any additional packages
Essentially the goal is to obtain a list of ID's of non production "services" in the most optimal way.

Here you go:
data = {
"service": [
{"name": ["Production"],
"id": ["256212"]
},
{"name": ["Non-Production"],
"id": ["256213"]}
]
}
for item in data["service"]:
if "Non-Production" in item["name"]:
print(item["id"])

Whatever I see JSON I think about functionnal programming ! Anyone else ?!
I think it is a better idea if you use function like concat or flat, filter and reduce, etc.
Egg one liner:
[s.get('id', [0])[0] for s in filter(lambda srv : "Non-Production" not in srv.get('name', []), data.get('service', {}))]
EDIT:
I updated the code, even if data = {}, the result will be [] an empty id list.

Mongodb Pymongo using $set to create an array/list/collection

I'm trying to use $set to create an array/list/collection (not sure which is proper terminology), and I'm not sure how to do it. For example:
I have a document inserted into my database that looks like this:
"_id": (unique, auto-generated id)
"Grade": Sophomore
I want to insert a collection/list/array using update. So, basically I want this:
"_id": (unique, auto-generated id)
"Grade": Sophomore
"Information"{
"Class_Info": [
{"Class_Name": "Math"}
]
What I've been doing so far is using .update and dot notation. So, what I was trying to do was use $set like this:
collection.update({'_id': unique ID}, {'$set': {'Information.Class_Info.Class_Name': 'Math}})
However, what that is doing is making Class_Info a document and not a list/collection/array, so it's doing:
"_id": (unique id)
"Grade": Sophomore
"Information"{
"Class_Info": {
"Class_Name": "Math"
}
How do I specify that I want Class_Info to be a list? IF for some reason I absolutely cannot use $set to do this, it is very important that I can use dot notation because of the way the rest of my program works, so if I'm supposed to use something other than $set, can it have dot notation to specify where to insert the list? (I know $push is another option, but it doesn't use dot notation, so I can't really use it in my case).
Thanks!

If you want to do it with only one instruction but starting up from NOT having any key created yet, this is the only way to do it ($set will never create an array that's not explicit, like {$set: {"somekey": [] }}
db.test.update(
{ _id: "(unique id)" },
{ $push: {
"Information.Class_Info": { "Class_Name": "Math" }
}}
)
This query does the trick, push to a non-existing key Information.Class_Info, the object you need to create as an array. This is the only possible solution with only one instruction, using dot notation and that works.

There is a way to do it with one instructions, $set and dot notation, as follows:
db.test.updateOne(
{ _id: "my-unique-id" },
{ $set: {
"Information.Class_Info": [ { "Class_Name": "Math" } ]
}}
)
There is also a way to do it with two instructions and the array index in the dot notation, allowing you to use similar statements to add more array elements:
db.test.updateOne(
{ _id: "my-unique-id" },
{ $set: { "Information.Class_Info": [] }}
)
db.test.updateOne(
{ _id: "my-unique-id" },
{ $set: {
"Information.Class_Info.0": { "Class_Name": "Math" },
"Information.Class_Info.1": { "Class_AltName": "Mathematics" }
}}
)
Deviating from these options has interesting failure modes:
If you try to combine the second option into a single updateOne() call, which is usually possible, MongoDB will complain that "Updating the path 'Information.Class_Info.0' would create a conflict at 'Information.Class_Info'"
If you try to use dot the notation with the array index ("Information.Class_Info.0.Class_Name": "Math") but without creating an empty array first, then MongoDB will create an object with numeric keys ("0", "1", …). It really refuses to create array except when told explicitly using […] (as also told in the answer by #Maximiliano).