Python Array JSON (dumps) - arrays

Question

Google App Engine, Python27
I am trying to encode a python array of strings to a JSON string to send to the client. I created a working solution, which requires me to manually create a string version of the array and call dumps on it from python, but I don't believe it should be necessary:
def get_json(cls):
name_query = cls.query()
array_string = "["
index = 1
for name in name_query:
array_string += '"' + name.key.id() + '"'
if index < name_query.count():
array_string += ", "
index += 1
array_string += "]"
return json.dumps(array_string)
>> "[\"Billy\", \"Bob\"]"
For my second attempt, I tried calling "dumps" on a python array, which I believe should be a working solution; instead, I have to call dumps twice:
# (bad output)
def get_json(cls):
name_query = cls.query()
name_array = []
for name in name_query:
name_array.append(name.key.id())
return json.dumps(name_array)
>> ["Billy", "Bob"]
# (working output)
def get_json(cls):
name_query = cls.query()
name_array = []
for name in name_query:
name_array.append(name.key.id())
return json.dumps(json.dumps(name_array)))
>> "[\"Billy\", \"Bob\"]"
Even though I have a working solution, is there a better way and why does calling dumps on a python array not give the correct output?

Answer 1

The first function is working fine; it's outputting a valid JSON string. I think the confusion for you is that it's not surrounded in double-quotes, but that's just because you're printing the output of the function.
It's returning a string containing a JSON list, not a Python list object:
>>> def get_json():
... x = ["Billy", "Bob"]
... return json.dumps(x)
...
>>> print get_json()
["Billy", "Bob"]
>>> print repr(get_json())
'["Billy", "Bob"]' # It's a string, not a list
>>> type(get_json())
<type 'str'> # See? Type is str
When you call json.dumps twice, you're just wrapping the Python string returned by the first json.dumps call in double-quotes, and the double-quotes that were inside the array get escaped, because they're embedded in one big JSON string now, instead of being used as quotes around JSON strings inside a JSON array.
>>> print repr(json.dumps(get_json()))
'"[\\"Billy\\", \\"Bob\\"]"'