converts a stream from JSON to CSV

json2csv.py

#!/usr/bin/env python

import csv, json, sys, cStringIO, codecs
from operator import itemgetter

def fmt(s):
  if s == None:
    return ''
  elif isinstance(s, basestring):
    return s.encode('utf-8')
  else:
    return unicode(s)

csv.register_dialect('psql', quoting=csv.QUOTE_ALL)

class UnicodeWriter:
    """
    A CSV writer which will write rows to CSV file "f",
    which is encoded in the given encoding.
    """

    def __init__(self, f, dialect='psql', encoding="utf-8", **kwds):
        # Redirect output to a queue
        self.queue = cStringIO.StringIO()
        self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
        self.stream = f
        self.encoder = codecs.getincrementalencoder(encoding)()

    def writerow(self, row):
        self.writer.writerow([fmt(s) for s in row])
        # Fetch UTF-8 output from the queue ...
        data = self.queue.getvalue()
        data = data.decode("utf-8")
        # ... and reencode it into the target encoding
        data = self.encoder.encode(data)
        # write to the target stream
        self.stream.write(data)
        # empty queue
        self.queue.truncate(0)

    def writerows(self, rows):
        for row in rows:
            self.writerow(row)

writer = UnicodeWriter(sys.stdout)
headers = []
access = None
for row in sys.stdin:
  j = json.loads(row)
  if not headers:
    headers = j.keys()
    writer.writerow(headers)
    access = itemgetter(*headers)
  else:
    writer.writerow(access(j))