检查python中是否存在json响应行

Question

Here is my json response

{u'kind': u'bigquery#queryResponse', u'rows': [{u'f': [{u'v': u'1'}, {u'v': u'1607'}, {u'v': u'coriolanus'}]}, {u'f': [{u'v': u'1'}, {u'v': u'1596'}, {u'v': u'kingjohn'}]}, {u'f': [{u'v': u'1'}, {u'v': u'1599'}, {u'v': u'kinghenryv'}]}, {u'f': [{u'v': u'1'}, {u'v': u'1600'}, {u'v': u'merrywivesofwindsor'}]}, {u'f': [{u'v': u'1'}, {u'v': u'1602'}, {u'v': u'troilusandcressida'}]}, {u'f': [{u'v': u'1'}, {u'v': u'1592'}, {u'v': u'comedyoferrors'}]}, {u'f': [{u'v': u'2'}, {u'v': u'1590'}, {u'v': u'3kinghenryvi'}]}, {u'f': [{u'v': u'2'}, {u'v': u'1612'}, {u'v': u'kinghenryviii'}]}, {u'f': [{u'v': u'2'}, {u'v': u'1598'}, {u'v': u'2kinghenryiv'}]}], u'jobReference': {u'projectId': u'1039435439624', u'jobId': u'job_ffb30cfb23674f88aa5cb497e358ec05'}, u'jobComplete': True, u'totalRows': u'9', u'schema': {u'fields': [{u'type': u'INTEGER', u'name': u'sum_for_the', u'mode': u'NULLABLE'}, {u'type': u'INTEGER', u'name': u'corpus_date', u'mode': u'NULLABLE'}, {u'type': u'STRING', u'name': u'f0_', u'mo de': u'NULLABLE'}]}}

I loop through this using the below python code

resp = []
for row in listReply['rows']:
  for key,dict_list in row.iteritems():
    count = dict_list[0]
    year = dict_list[1]
    corpus = dict_list[2]
    resp.append({'count': count['v'],'year':year['v'],'corpus':corpus['v']})

How to check if this listReply['rows'] exists or not as in case of a json response such as below

{u'totalRows': u'0', u'kind': u'bigquery#queryResponse', u'jobComplete': True, u'jobReference': {u'projectId': u'1039435439624', u'jobId': u'job_8efc645852c34515bcff4ab3969772fd'}, u'schema': {u'fields': [{u'type': u'INTEGER', u'name': u'sum_for_the', u'mode': u'NULLABLE'}, {u'type': u'INTEGER', u'name': u'corpus_date', u'mode': u'NULLABLE'}, {u'type': u'STRING', u'name': u'f0_', u'mode': u'NULLABLE'}]}}

Answer 1

for row in listReply.get('rows', []):

If listReply has a key "rows", this will iterate over the corresponding value. If the key doesn't exist, the default is returned, which should be an empty list in this case so for will not complain since it is iterable.

Another way is to test for the key before entering the for loop.

if 'rows' in listReply:
    for row in listReply['rows']:
        ...

Answer 2

You can use

if key in aDict:
  # Operations

To test for the existence of an entry in a python dictionary. If it'll be an empty list you can also do this:

if key in aDict and aDict[key]:
  # Operations

Because evaluation is left-to-right, if the key is missing the second check will not be performed, but if it is present and empty, the second check will skip the operations.

Answer 3

To check if a key exists in a dict use the in keyword.

>>> d = {}
>>> 1 in d
16: False
>>> d[1] = 1
>>> 1 in d
17: True
>>> d
18: {1: 1}

so to use your example

>>> d = {u'totalRows': u'0', u'kind': u'bigquery#queryResponse', u'jobComplete': True, u'jobReference': {u'projectId': u'1039435439624', u'jobId': u'job_8efc645852c34515bcff4ab3969772fd'}, u'schema': {u'fields': [{u'type': u'INTEGER', u'name': u'sum_for_the', u'mode': u'NULLABLE'}, {u'type': u'INTEGER', u'name': u'corpus_date', u'mode': u'NULLABLE'}, {u'type': u'STRING', u'name': u'f0_', u'mode': u'NULLABLE'}]}}
>>> 'rows' in d
19: False