I have an array of dictionaries but i am running into a scenario where I have to get the value from 1st index of the array of dictionaries, following is the chunk that I am trying to query.
address_data = record.get('Rdata')[0].get('Adata')
This throws the following error:
TypeError: 'NoneType' object is not subscriptable
I tried following:
if record.get('Rdata') and record.get('Rdata')[0].get('Adata'):
address_data = record.get('Rdata')[0].get('Adata')
but I don't know if the above approach is good or not.
So how to handle this in python?
Edit:
"partyrecord": {
"Rdata": [
{
"Adata": [
{
"partyaddressid": 172,
"addressid": 142165
}
]
}
]
}
Your expression assumes that record['Rdata'] will return a list with at least one element, so provide one if that isn't the case.
address_data = record.get('Rdata', [{}])[0].get('Adata')
Now if record['Rdata'] doesn't exist, you'll still have an empty dict on which to invoke get('Adata'). The end result will be address_data being set to None.
(Checking for the key first is preferable if a suitable default is expensive to create, since it will be created whether get needs to return it or not. But [{}] is fairly lightweight, and the compiler can generate it immediately.)
You might want to go for the simple, not exciting route:
role_data = record.get('Rdata')
if role_data:
address_data = role_data[0].get('Adata')
else:
address_data = None
Related
I come from a C++ background, I am new to Python, and I suspect this problem has something to do with [im]mutability.
I am building a JSON representation in Python that involves several layers of nested lists and dictionaries in one "object". My goal is to call jsonify on the end result and have it look like nicely structured data.
I hit a problem while building out an object:
approval_groups_list = list()
approval_group_dict = dict()
for groupMemKey, groupvals in groupsAndMembersDict.items():
approval_group_dict["group_name"] = groupMemKey
approval_group_dict["name_dot_numbers"] = groupvals # groupvals is a list of strings
approval_groups_list.append(approval_group_dict)
entity_approval_unit["approval_groups"] = approval_groups_list
The first run does as expected, but after, whatever groupMemkey is touched last, that is what all other objects mirror.
groupsAndMembersDict= {
'Art': ['string.1', 'string.2', 'string.3'],
'Math': ['string.10', 'string.20', 'string.30']
}
Expected result:
approval_groups:
[
{
"group_name": "Art",
"name_dot_numbers": ['string.1', 'string.2', 'string.3']
},
{
"group_name": "Math",
"name_dot_numbers": ['string.10', 'string.20', 'string.30']
}
]
Actual Result:
approval_groups:
[
{
"group_name": "Math",
"name_dot_numbers": ['string.10', 'string.20', 'string.30']
},
{
"group_name": "Math",
"name_dot_numbers": ['string.10', 'string.20', 'string.30']
}
]
What is happening, and how do I fix it?
Your problem is not the immutability, but the mutability of objects. I'm sure you would have ended up with the same result with the equivalent C++ code.
You construct approval_group_dict before the for loop and keep reusing it. All you have to do is to move the construction inside for so that a new object is created for each loop:
approval_groups_list = list()
for groupMemKey, groupvals in groupsAndMembersDict.items():
approval_group_dict = dict()
...
Through writing this question, it dawned on me to try a few things including this, which fixed my problem - however, I still don't know exactly why this works. Perhaps it is more like a pointer/referencing problem?
approval_groups_list = list()
approval_group_dict = dict()
for groupMemKey, groupvals in groupsAndMembersDict.items():
approval_group_dict["group_name"] = groupMemKey
approval_group_dict["name_dot_numbers"] = groupvals
approval_groups_list.append(approval_group_dict.copy()) # <== note, here is the difference ".copy()"
entity_approval_unit["approval_groups"] = approval_groups_list
EDIT: The problem turns out to be that Python is Pass by [object] reference all the time. If you are new to Python like me, this means: "pass by reference, except when the thing you are passing is immutable, then its pass by value". So in a way it did have to do with [im]mutability. Mostly it had to do with my lack of understanding how Python passes references.
I'm using Lambda to run through my AWS account, returning a list of all instances. I need to be able to print out all of the 'VolumeId' values, but I can't work out how to access them as they are nested. I am able to print out the first VolumeId for each instance, however, some of the instances have several volumes, and some only have one. I think I know why I get these results, but I can't work out what to do to get all of them back.
Here's a snippet of what the JSON for one instance looks like:
{
'Groups':[],
'Instances':[
{
'AmiLaunchIndex':0,
'ImageId':'ami-0',
'InstanceId':'i-0123',
'InstanceType':'big',
'KeyName':'nonprod',
'LaunchTime':'date',
'Monitoring':{
'State':'disabled'
},
'Placement':{
'AvailabilityZone':'world',
'GroupName':'',
'Tenancy':'default'
},
'PrivateDnsName':'secret',
'PrivateIpAddress':'1.2.3.4',
'ProductCodes':[
],
'PublicDnsName':'',
'State':{
'Code':80,
'Name':'stopped'
},
'StateTransitionReason':'User initiated',
'SubnetId':'subnet-1',
'VpcId':'vpc-1',
'Architecture':'yes',
'BlockDeviceMappings':[
{
'DeviceName':'/sda',
'Ebs':{
'AttachTime':'date',
'DeleteOnTermination':True,
'Status':'attached',
'VolumeId':'vol-1'
}
},
{
'DeviceName':'/sdb',
'Ebs':{
'AttachTime':'date'),
'DeleteOnTermination':False,
'Status':'attached',
'VolumeId':'vol-2'
}
}
],
This is what I'm doing to get the first VolumeId:
ec2client = boto3.client('ec2')
ec2 = ec2client.describe_instances()
for reservation in ec2["Reservations"]:
for instance in reservation["Instances"]:
instanceid = instance["InstanceId"]
volumes = instance["BlockDeviceMappings"][0]["Ebs"]["VolumeId"]
print("The associated volume IDs for this instance are: ",(volumes))
I think the reason that I'm getting just the first ID is because I'm referencing the first element within "BlockDeviceMappings", but I can't work out how to get the other ones. If I try it without specifying the [0], I get the list indices must be integers or slices, not str error. I tried to use a dictionary instead of a list too, but felt like I was barking up the wrong tree with that one. Any suggestions/help would be appreciated!
One possible answer, not particularly pythonic
...
id_list = []
volumes_data = instance["BlockDeviceMappings"]
for element in volumes_data:
id_list.append(element["Ebs"]["VolumeId"])
Or else use json.loads and then iterate though json using .get syntax like the final answer in this
So I'm trying to access the following JSON data with python and when i give the statement :
print school['students']
The underlying data gets printed but what I really want to be able to do is print the 'id' value.
{ 'students':[
{
'termone':{
'english':'fifty',
'science':'hundred'
},
'id':'RA1081310005'
}
]
}
So when I do the following I get an error :
print school ['students']['id']
TypeError: list indices must be integers, not str
Can anyone suggest how i can access the ID & where I'm going wrong!
school['students'] is a list. You are trying to access the first element of that list and id key belongs to that element. Instead, try this:
school['students'][0]['id']
Out: 'RA1081310005'
The problem here is that in your list, 'id' is not a part of a dictionary, it is part of a list. To fix this, change your dictionary to the following:
school = {'students':{
'termone': {
"english": "fifty:,
"science": "hundred
},
"id":"RA1081310005"
}
}
Basically, you have a list, and there is no reason to have it, so I removed it.
I apologize in advance that the title is so confusing. It makes a lot more sense in code, so here goes:
I am parsing data from a REST API that returns JSON, and I have a bit of an issue with this particular structure:
{ 'Order' : [
{ 'orderID': '1',
'OrderLines': {
'OrderLine': [
{ 'lineID':'00001', 'quantity':'1', 'cost':'10', 'description':'foo' },
{ 'lineID':'00002', 'quantity':'2', 'cost':'23.42', 'description':'bar' }
]}
}
{ 'orderID': '2',
'OrderLines': {
'OrderLine':
{ 'lineID':'00003', 'quantity':'6', 'cost':'12.99', 'description':'lonely' }
}
}
]}
If you'll notice, the second order only has one OrderLine, so instead of returning a list containing dictionaries, it returns the dictionary. Here is what I am trying to do:
orders_json = json.loads(from_server)
for order in orders_json['Order']:
print 'Order ID: {}'.format(order['orderID'])
for line in order['OrderLines']['OrderLine']:
print '-> Line ID: {}, Quantity: {}'.format(line['lineID'], line['quantity'])
It works just fine for the first order, but the second order throws TypeError: string indices must be integers since line is now a string containing the dictionary, instead of a dictionary from the list. I've been banging my head against this for hours now, and I feel like I am missing something obvious.
Here are some of the things I have tried:
Using len(line) to see if it gave me something unique for the one line orders. It does not. It returns the number of key:value pairs in the dictionary, which in my real program is 10, which an order containing 10 lines would also return.
Using a try/except. Well, that stops the TypeError from halting the whole thing, but I can't figure out how to address the dictionary once I've done that. Line is a string for single line orders instead of a dictionary.
Whoever designed that API did not do a terribly good job. Anyway, you could check whether OrderLine is a list and, if it's not, wrap it in a one-element list before doing any processing:
if not isinstance(order_line, list):
order_line = [order_line]
That would work, my personal preference would be to get the API fixed.
I'd check if the type is correct and then convert it to a list if necessary to have a uniform access:
lines = order['OrderLines']['OrderLine']
lines = [lines] if not isinstance(lines, list) else lines
for line in lines:
...
You can check the type of the object you try to access:
# ...
print 'Order ID: {0}'.format(order['orderID'])
lines = order['OrderLines']['OrderLine']
if isinstance(lines, list):
for line in lines:
print line['lineID']
elif isinstance(lines, dict):
print lines['lineID']
else:
raise ValueError('Illegal JSON object')
Edit: Wrapping the dict in a list as proposed by #NPE is the nicer and smarter solution.
I'm having troubles parsing a complicated json. That is it:
{
"response": {
"players": [
{
"bar": "76561198034360615",
"foo": "49329432943232423"
}
]
}
}
My code:
url = urllib.urlopen("foobar").read()
js = json.load(url)
data = js['response']
print data['players']
The problem is that this would print the dict. What I want is to reach the key's values, like foo and bar. What I tried so far is doing data['players']['foo'] and it gives me an error that list indices should be integers, I tried of course, it didn't work. So my question is how do I reach these values? Thanks in advance.
data['response']['players'] is an array (as defined by the brackets ([, ]), so you need to access items using a specific index (0 in this case):
data['players'][0]['foo']
Or iterate over all players:
for player in data['response']['players']:
print player['foo']
The problem is that players is a list of items ([ ] in json). So you need to select the first and only item in this case using [0].
print data['players'][0]['foo']
But, keep in mind that you may have more than one player, in which case you either need to specify the player, or loop through the players using a for loop
for player in data['players']:
print player['foo']