Create CSV row using CSV library from JSON Object using StringIO

json_to_csv_using_stringio.py

import csv
import json
import StringIO

'''
Create CSV row using CSV library from JSON Object using StringIO
'''

json_doc = '{"key1":"value1","key2":"value2","key3":"value3"}'	# JSON Document as Text
csv_doc_field = ['key1','key2']					# Field to be processed
csv_doc = StringIO.StringIO()					# 'False' file to use with CSV Writer
json_doc = json.loads(json_doc)					# Create JSON Object
output = csv.writer(csv_doc)					# Create CSV writer using StringIO file			

tt = list()							# Field list
for field in csv_doc_field:					# Loop each field
	tt.append(json_doc[field])				# Append each value processed
    
output.writerow(tt)						# Write row into StringIO file
print csv_doc.getvalue()					# Show result -> value1,value2
csv_doc.close()							# Close StringIO file

Ahórrate el for con list comprehension :)
output.writerow([x[1] for x in json_doc.iteritems() if x[0] in csv_doc_field])