Python: extracting a list from an array of dictionaries with arrays in them

Question

This question is a bit of a convoluted brain-twister, I'm afraid. I'm writing a function test on an api, that when I query it, returns a bunch of json with embedded lists. Here is a significant fragment of what that looks like (with all the data anonymized for this question):

[{u'account': {u'account_name': u'Autotest Account',
               u'account_uid': u'000000000'},
  u'address': {u'city': u'AutoTest City',
               u'country': u'United States',
               u'postal_code': u'10019',
               u'province': None,
               u'state': u'IL',
               u'street': [u'12 Auto Road']},
  u'children': [{u'institution_name': u'Autotest Bottom Institution 1',
                 u'institution_type': 1,
                 u'institution_uid': u'111111111'},
                {u'institution_name': u'Autotest Bottom Institution 2',
                 u'institution_type': 1,
                 u'institution_uid': u'222222222'},
                {u'institution_name': u'Autotest Bottom Institution 3',
                 u'institution_type': 1,
                 u'institution_uid': u'333333333'},
                {u'institution_name': u'Autotest Bottom Institution 4',
                 u'institution_type': 1,
                 u'institution_uid': u'444444444'},
                {u'institution_name': u'Autotest Bottom Institution 5',
                 u'institution_type': 1,
                 u'institution_uid': u'555555555'},
                {u'institution_name': u'Autotest Bottom Institution 6',
                 u'institution_type': 1,
                 u'institution_uid': u'666666666'},
                {u'institution_name': u'Autotest Bottom Institution 7',
                 u'institution_type': 1,
                 u'institution_uid': u'777777777'},
                {u'institution_name': u'Autotest Bottom Institution 8',
                 u'institution_type': 1,
                 u'institution_uid': u'888888888'}],
  u'institution_name': u'Autotest Middle Institution 1',
  u'institution_type': 2,
  u'institution_uid': u'000000001',
  u'parent': {u'institution_name': u'Autotest Top Institution',
              u'institution_type': 3,
              u'institution_uid': u'000000099'},
  u'school_year': 2011},
 {u'account': {u'account_name': u'Autotest Account',
               u'account_uid': u'000000000'},
  u'address': {u'city': u'Bacon City',
               u'country': u'United States',
               u'postal_code': u'10018',
               u'province': None,
               u'state': u'IL',
               u'street': [u'15 Wonder Road']},
  u'children': [],
  u'institution_name': u'Autotest Bottom Institution 1',
  u'institution_type': 1,
  u'institution_uid': u'111111111',
  u'parent': {u'institution_name': u'Autotest Middle Institution 1',
              u'institution_type': 2,
              u'institution_uid': u'000000001'},
  u'school_year': 2011}]

What I'm trying to accomplish, is to extract all of the "Bottom Institution" names from the JSON, and put them into a list that I can then compare to a list that's already in my test fixture data. It should look something like this:

['Autotest Bottom Institution 1','Autotest Bottom Institution 2','Autotest Bottom Institution 3','Autotest Bottom Institution 4','Autotest Bottom Institution 5','Autotest Bottom Institution 6','Autotest Bottom Institution 7','Autotest Bottom Institution 8']

I'm able to extract them one-at-a-time or via iteration, after loading the data into "inst_array", like this:

>>> print inst_array[0]['children'][0]['institution_name']
Autotest Bottom Institution 1
>>> print inst_array[0]['children'][1]['institution_name']
Autotest Bottom Institution 2
>>> print inst_array[0]['children'][2]['institution_name']
Autotest Bottom Institution 3

But here's the kicker: I want to be able to do this without iteration (or, with as little iteration as possible), and because of the umpteen layers of nesting in this, It's got me puzzled.

Any thoughts?

Kenan Banks · Accepted Answer · 2010-11-02 17:26:26Z

5

Shouldn't something like this work?

names = [child['institution_name'] for child in inst_array[0]['children']]

answered Nov 2, 2010 at 17:26

Kenan Banks

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1 Comment

Greg Gauthier Over a year ago

you sir, are a genius. Yeah, that's exactly what I wanted. For some reason, when I tried this, I couldn't get "child['institution_name'] to work. I'll have to go back and look at my notes...

UncleZeiv · Accepted Answer · 2010-11-02 17:27:02Z

1

I guess a list comprehension is still a form of iteration, but at least concise:

your_list = [elem['institution_name'] for elem in inst_array[0]['children']]

answered Nov 2, 2010 at 17:27

UncleZeiv

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Daniel Roseman · Accepted Answer · 2010-11-02 17:27:12Z

0

Not sure about what you mean by 'without iteration'. Whatever you do here has to involve iterating through the lists, by definition.

Anyway, here's an attempt:

institutions = set()
for account in data:
    for child in account['children']:
        institutions.add(child['institution_name'])

answered Nov 2, 2010 at 17:27

Daniel Roseman

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1 Comment

Greg Gauthier Over a year ago

sorry about the confused language - you're quite right. I was looking for a list comprehension technique, which technically still is iteration, but in a short-hand form. :/

Vinko Vrsalovic · Accepted Answer · 2010-11-02 17:27:34Z

0

I'm not sure what do you mean exactly with "without iteration", but here is something with implied iteration that could work:

 [x['institution_name'] for x in inst_array[0]['children'] if x['institution_name']]

answered Nov 2, 2010 at 17:27

Vinko Vrsalovic

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Comments

Douglas Leeder · Accepted Answer · 2010-11-02 18:17:31Z

0

Something like:

[ x['institution_name'] for x in inst_array[0]['children'] ]

answered Nov 2, 2010 at 18:17

Douglas Leeder

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