python json stream encoding of generator and array / list using stdlib

json_stream_encoding_stdlib.py

# You can use the builtin json lib to iteratively encode a json object
# but encoding a json array iteratively requires the iterable to be list-like
# No worries we just subclass list and pretend to be a list while being able to ingest 
# whatever you want


import json
import sys

class IteratorAsList(list):
    def __init__(self, it):
        self.it = it
    def __iter__(self):
        return self.it
    def __len__(self):
        return 1

generator = ("lolcat" for i in range(10))
for index, chunk in enumerate(
        json.JSONEncoder().iterencode(IteratorAsList(generator))
    ):
    sys.stdout.write(chunk)    
    sys.stdout.flush()
    break

# produces:
# ["lolcat"
# which means that the first chunk included the array start bracket
# and the first array member
print()

generator = ("lolcat" for i in range(10))
for index, chunk in enumerate(
        json.JSONEncoder().iterencode(IteratorAsList(generator))
    ):
    sys.stdout.write(chunk)    
    sys.stdout.flush()

# produces 
# ["lolcat", "lolcat", "lolcat", "lolcat", "lolcat", "lolcat", "lolcat", "lolcat", "lolcat", "lolcat"]
# one line with start and end brackets