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Write a custom JSON interpreter for a file that looks like json but isnt using Python

What I need to do is to write a module that can read and write files that use the PDX script language. This language looks alot like json but has enough differences that a custom encoder/decoder is needed to do anything with those files (without a mess of regex substitutions which would make maintenance hell). I originally went with just reading them as txt files, and use regex to find and replace things to convert it to valid json. This lead me to my current point, where any additions to the code requires me to write far more code than I would want to, just to support some small new thing. So using a custom json thing I could write code that shows what valid key:value pairs are, then use that to handle the files. To me that will be alot less code and alot easier to maintain.
So what does this code look like? In general it looks like this (tried to put all possible syntax, this is not an example of a working file):
#key = value # this is the definition for the scripted variable
key = {
# This is a comment. No multiline comments
function # This is a single key, usually optimize_memory
# These are the accepted key:value pairs. The quoted version is being phased out
key = "value"
key = value
key = #key # This key is using a scripted variable, defined either in the file its in or in the `scripted_variables` folder. (see above for example on how these are initially defined)
# type is what the key type is. Like trigger:planet_stability where planet_stability is a trigger
key = type:key
# Variables like this allow for custom names to be set. Mostly used for flags and such things
[[VARIABLE_NAME]
math_key = $VARIABLE_NAME$
]
# this is inline math, I dont actually understand how this works in the script language yet as its new. The "<" can be replaced with any math symbol.
# Valid example: planet_stability < #[ stabilitylevel2 + 10 ]
key < #[ key + 10 ]
# This is used alot to handle code blocks. Valid example:
# potential = {
# exists = owner
# owner = {
# has_country_flag = flag_name
# }
# }
key = {
key = value
}
# This is just a list. Inline brackets are used alot which annoys me...
key = { value value }
}
The major differences between json and PDX script is the nearly complete lack of quotations, using an equals sign instead of a colon for separation and no comma's at the end of the lines. Now before you ask me to change the PDX code, I cant. Its not mine. This is what I have to work with and cant make any changes to the syntax. And no I dont want to convert back and forth as I have already mentioned this would require alot of work. I have attempted to look for examples of this, however all I can find are references to convert already valid json to a python object, which is not what I want. So I cant give any examples of what I have already done, as I cant find anywhere to even start.
Some additional info:
Order of key:value pairs does not technically matter, however it is expected to be in a certain order, and when not in that order causes issues with mods and conflict solvers
bool properties always use yes or no rather than true or false
Lowercase is expected and in some cases required
Math operators are used as separators as well, eg >=, <= ect
The list of syntax is not exhaustive, but should contain most of the syntax used in the language
Past work:
My last attempts at this all revolved around converting it from a text file to a json file. This was alot of work just to get a small piece of this to work.
Example:
potential = {
exists = owner
owner = {
is_regular_empire = yes
is_fallen_empire = no
}
NOR = {
has_modifier = resort_colony
has_modifier = slave_colony
uses_habitat_capitals = yes
}
}
And what i did to get most of the way to json (couldnt find a way to add quotes)
test_string = test_string.replace("\n", ",")
test_string = test_string.replace("{,", "{")
test_string = test_string.replace("{", "{\n")
test_string = test_string.replace(",", ",\n")
test_string = test_string.replace("}, ", "},\n")
test_string = "{\n" + test_string + "\n}"
# Replace the equals sign with a colon
test_string = test_string.replace(" =", ":")
This resulted in this:
{
potential: {
exists: owner,
owner: {
is_regular_empire: yes,
is_fallen_empire: no,
},
NOR: {
has_modifier: resort_colony,
has_modifier: slave_colony,
uses_habitat_capitals: yes,
},
}
}
Very very close yes, but in no way could I find a way to add the quotations to each word (I think I did try a regex sub, but wasnt able to get it to work, since this whole thing is just one unbroken string), making this attempt stuck and also showing just how much work is required just to get a very simple potential block to mostly work. However this is not the method I want anymore, one because its alot of work and two because I couldnt find anything to finish it. So a custom json interpreter is what I want.

The classical approach (potentially leading to more code, but also more "correctness"/elegance) is probably to build a "recursive descent parser", from a bunch of conditionals/checks, loops and (sometimes recursive?) functions/handlers to deal with each of the encountered elements/characters on the input stream. An implicit parse/call tree might be sufficient if you directly output/print the JSON equivalent, or otherwise you could also create a representation/model in memory for later output/conversion.
Related book recommendation could be "Language Implementation Patterns" by Terence Parr, me avoiding to promote my own interpreters and introductory materials :-) In case you need further help, maybe write me?

looping through json python is very slow

Can someone help me understand what I'm doing wrong in the following code:
def matchTrigTohost(gtriggerids,gettriggers):
mylist = []
for eachid in gettriggers:
gtriggerids['params']['triggerids'] = str(eachid)
hgetjsonObject = updateitem(gtriggerids,processor)
hgetjsonObject = json.dumps(hgetjsonObject)
hgetjsonObject = json.loads(hgetjsonObject)
hgetjsonObject = eval(hgetjsonObject)
hostid = hgetjsonObject["result"][0]["hostid"]
hname = hgetjsonObject["result"][0]["name"]
endval = hostid + "--" + hname
mylist.append(endval)
return(hgetjsonObject)
The variable gettriggers contain a lot of ids (~3500):
[ "26821", "26822", "26810", ..... ]
I'm looping through the ids in the variable and assigning them to a json object.
gtriggerids = {
"jsonrpc": "2.0",
"method": "host.get",
"params": {
"output": ["hostid", "name"],
"triggerids": "26821"
},
"auth": mytoken,
"id": 2
}
When I run the code against the above json variable, it is very slow. It is taking several minutes to check each ID. I'm sure I'm doing many things wrong here or at least not in the pythonic way. Can anyone help me speed this up? I'm very new to python.
NOTE:
The dump() , load(), eval() were used to convert the str produced to json.

You asked for help knowing what you're doing wrong. Happy to oblige :-)
At the lowest level—why your function is running slowly—you're running many unnecessary operations. Specifically, you're moving data between formats (python dictionaries and JSON strings) and back again which accomplishes nothing but wasting CPU cycles.
You mentioned this is only way you could get the data in the format you needed. That brings me to the second thing you're doing wrong.
You're throwing code at the wall instead of understanding what's happening.
I'm quite sure (and several of your commenters appear to agree) that your code is not the only way to arrange your data into a usable structure. What you should do instead is:
Understand as much as you can about the data you're being given. I suspect the output of updateitem() should be your first target of learning.
Understand the right/typical way to interact with that data. Your data doesn't have to be a dictionary before you can use it. Maybe it's not the best approach.
Understand what regularities and irregularities the data may have. Part of your problem may not be with types or dictionaries, but with an unpredictable/dirty data source.
Armed with all this new knowledge, manipulate your as simply as you can.
I can pretty much guarantee the result will run faster.
More detail! Some things you wrote suggest misconceptions:
I'm looping through the ids in the variable and assigning them to a json object.
No, you can't assign to a JSON object. In python, JSON data is always a string. You probably mean that you're assigning to a python dictionary, which (sometimes!) can be converted to a JSON object, represented as a string. Make sure you have all those concepts clear before you move forward.
The dump() , load(), eval() were used to convert the str produced to json.
Again, you don't call dumps() on a string. You use that to convert a python object to a string. Run this code in a REPL, go step by step, and inspect or play with each output to understand what it is.

Python 2.7 replace all instances of NULL / NONE in complex JSON object

I have the following code..
.... rest api call >> response
rsp = response.json()
print json2html.convert(rsp)
which results in the following
error: Can't convert NULL!
I therefore started looking into schemes to replace all None / Null's in my JSON response, but I'm having an issue since the JSON returned from the api is complex and nested many levels and I don't know where the NULL will actually appear.
From what I can tell I need to iterate over the dictionary objects recursively and check for any values that are NONE and actually rebuild the object with the values replaced, but I don't really know where to start since dictionary objects are immutable..

If you look at json2html's source it seems like you have a different problem - and the error message is not helping.
Try to use it like this:
print json2html.convert(json=rsp)
btw. because I've already contributed to that project a bit I've opened up the following PR due to this question: https://github.com/softvar/json2html/pull/20

Using boto (AWS Python), how do I get a list of IAM users?

Newbie question. I'm expecting to be able to do something like the following:
import boto
from boto.iam.connection import IAMConnection
cfn = IAMConnection()
cfn.get_all_users()
for user in userList:
print user.user_id
The connection works fine, but the last line returns the error "'unicode' object has no attribute 'user_id'".
I did a type(userList) and it reported the type as <class 'boto.jsonresponse.Element'>, which doesn't appear (?) to be documented. Using normal JSON parsing doesn't appear to work either.
From another source, it looks as if the intent is the results of an operation like this are supposed to be "pythonized."
Anyway, I'm pretty new to boto, so I assume there's some simple way to do this that I just haven't stumbled across.
Thx!

For some of the older AWS services, boto takes the XML responses from the service and turns them into nice Python objects. For others, it takes the XML response and transliterates it directly into native Python data structures. The boto.iam module is of the latter form. So, the actual data returned by get_all_users() looks like this:
{u'list_users_response':
{u'response_metadata': {u'request_id': u'8d694cbd-93ec-11e3-8276-993b3edf6dba'},
u'list_users_result': {u'users':
[{u'path': u'/', u'create_date': u'2014-01-21T17:19:45Z', u'user_id':
u'<userid>', u'arn': u'<arn>', u'user_name': u'foo'},
{...next user...}
]
}
}
So, all of the data you want is there, it's just a bit difficult to find. The boto.jsonresponse.Element object returned does give you a little help. You can actually do something like this:
data = cfn.get_all_users()
for user in data.user:
print(user['user_name'])
but for the most part you just have to dig around in the data returned to find what you are looking for.

How to inspect mystery deserialized object in Python

I'm trying to load JSON back into an object. The "loads" method seems to work without error, but the object doesn't seem to have the properties I expect.
How can I go about examining/inspecting the object that I have (this is web-based code).
results = {"Subscriber": {"firstname": "Neal", "lastname": "Walters"}}
subscriber = json.loads(results)
for item in inspect.getmembers(subscriber):
self.response.out.write("<BR>Item")
for subitem in item:
self.response.out.write("<BR> SubItem=" + subitem)
The attempt above returned this:
Item
SubItem=__class__
I don't think it matters, but for context:
The JSON is actually coming from a urlfetch in Google App Engine to
a rest web service created using this utility:
http://code.google.com/p/appengine-rest-server.
The data is being retrieved from a datastore with this definition:
class Subscriber(db.Model):
firstname = db.StringProperty()
lastname = db.StringProperty()
Thanks,
Neal
Update #1: Basically I'm trying to deserialize JSON back into an object.
In theory it was serialized from an object, and I want to now get it back into an object.
Maybe the better question is how to do that?
Update #2: I was trying to abstract a complex program down to a few lines of code, so I made a few mistakes in "pseudo-coding" it for purposes of posting here.
Here's a better code sample, now take out of website where I can run on PC.
results = '{"Subscriber": {"firstname": "Neal", "lastname": "Walters"}}'
subscriber = json.loads(results)
for key, value in subscriber.items():
print " %s: %s" %(key, value)
The above runs, what it displays doesn't look any more structured than the JSON string itself. It displays this:
Subscriber: {u'lastname': u'Walters', u'firstname': u'Neal'}
I have more of a Microsoft background, so when I hear serialize/deserialize, I think going from an object to a string, and from a string back to an object. So if I serialize to JSON, and then deserialize, what do I get, a dictionary, a list, or an object? Actually, I'm getting the JSON from a REST webmethod, that is on my behalf serializing my object for me.
Ideally I want a subscriber object that matches my Subscriber class above, and ideally, I don't want to write one-off custom code (i.e. code that would be specific to "Subscriber"), because I would like to do the same thing with dozens of other classes. If I have to write some custom code, I will need to do it generically so it will work with any class.
Update #3: This is to explain more of why I think this is a needed tool. I'm writing a huge app, probably on Google App Engine (GAE). We are leaning toward a REST architecture for several reasons, but one is that our web GUI should access the data store via a REST web layer. (I'm a lot more used to SOAP, so switching to REST is a small challenge in itself). So one of the classic ways of getting and update data is through a business or data tier. By using the REST utility mention above, I have the choice of XML or JSON. I'm hoping to do a small working prototype of both before we develop the huge app). Then, suppose we have a successful app, and GAE doubles it prices. Then we can rewrite just the data tier, and take our Python/Django user tier (web code), and run it on Amazon or somewhere else.
If I'm going to do all that, why would I want everything to be dictionary objects. Wouldn't I want the power of full-blown class structure? One of the next tricks is sort of an object relational mapping (ORM) so that we don't necessarily expose our exact data tables, but more of a logical layer.
We also want to expose a RESTful API to paying users, who might be using any language. For them, they can use XML or JSON, and they wouldn't use the serialize routine discussed here.

json only encodes strings, floats, integers, javascript objects (python dicts) and lists.
You have to create a function to turn the returned dictionary into a class and then pass it to a json.loads using the object_hook keyword argument along with the json string. Heres some code that fleshes it out:
import json
class Subscriber(object):
firstname = None
lastname = None
class Post(object):
author = None
title = None
def decode_from_dict(cls,vals):
obj = cls()
for key, val in vals.items():
setattr(obj, key, val)
return obj
SERIALIZABLE_CLASSES = {'Subscriber': Subscriber,
'Post': Post}
def decode_object(d):
for field in d:
if field in SERIALIZABLE_CLASSES:
cls = SERIALIZABLE_CLASSES[field]
return decode_from_dict(cls, d[field])
return d
results = '''[{"Subscriber": {"firstname": "Neal", "lastname": "Walters"}},
{"Post": {"author": {"Subscriber": {"firstname": "Neal",
"lastname": "Walters"}}},
"title": "Decoding JSON Objects"}]'''
result = json.loads(results, object_hook=decode_object)
print result
print result[1].author
This will handle any class that can be instantiated without arguments to the constructor and for which setattr will work.
Also, this uses json. I have no experience with simplejson so YMMV but I hear that they are identical.
Note that although the values for the two subscriber objects are identical, the resulting objects are not. This could be fixed by memoizing the decode_from_dict class.

results in your snippet is a dict, not a string, so the json.loads would raise an exception. If that is fixed, each subitem in the inner loop is then a tuple, so trying to add it to a string as you are doing would raise another exception. I guess you've simplified your code, but the two type errors should already show that you simplified it too much (and incorrectly). Why not use an (equally simplified) working snippet, and the actual string you want to json.loads instead of one that can't possibly reproduce your problem? That course of action would make it much easier to help you.
Beyyond peering at the actual string, and showing some obvious information such as type(subscriber), it's hard to offer much more help based on that clearly-broken code and such insufficient information:-(.
Edit: in "update2", the OP says
It displays this: Subscriber: {u'lastname': u'Walters', u'firstname': u'Neal'}
...and what else could it possibly display, pray?! You're printing the key as string, then the value as string -- the key is a string, and the value is another dict, so of course it's "stringified" (and all strings in JSON are Unicode -- just like in C# or Java, and you say you come from a MSFT background, so why does this surprise you at all?!). str(somedict), identically to repr(somedict), shows the repr of keys and values (with braces around it all and colons and commas as appropriate separators).
JSON, a completely language-independent serialization format though originally centered on Javascript, has absolutely no idea of what classes (if any) you expect to see instances of (of course it doesn't, and it's just absurd to think it possibly could: how could it possibly be language-independent if it hard-coded the very concept of "class", a concept which so many languages, including Javascript, don't even have?!) -- so it uses (in Python terms) strings, numbers, lists, and dicts (four very basic data types that any semi-decent modern language can be expected to have, at least in some library if not embedded in the language proper!). When you json.loads a string, you'll always get some nested combination of the four datatypes above (all strings will be unicode and all numbers will be floats, BTW;-).
If you have no idea (and don't want to encode by some arbitrary convention or other) what class's instances are being serialized, but absolutely must have class instances back (not just dicts etc) when you deserialize, JSON per se can't help you -- that metainformation cannot possibly be present in the JSON-serialized string itself.
If you're OK with the four fundamental types, and just want to see some printed results that you consider "prettier" than the default Python string printing of the fundamental types in question, you'll have to code your own recursive pretty-printing function depending on your subjective definition of "pretty" (I doubt you'd like Python's own pprint standard library module any more than you like your current results;-).

My guess is that loads is returning a dictionary. To iterate over its content, use something like:
for key, value in subscriber.items():
self.response.out.write("%s: %s" %(key, value))