[python] Single vs double quotes in JSON

My code:

import simplejson as json

s = "{'username':'dfdsfdsf'}" #1
#s = '{"username":"dfdsfdsf"}' #2
j = json.loads(s)

#1 definition is wrong

#2 definition is right

I heard that in Python that single and double quote can be interchangable. Can anyone explain this to me?

I recently came up against a very similar problem, and believe my solution would work for you too. I had a text file which contained a list of items in the form:

["first item", 'the "Second" item', "thi'rd", 'some \\"hellish\\" \'quoted" item']

I wanted to parse the above into a python list but was not keen on eval() as I couldn't trust the input. I tried first using JSON but it only accepts double quoted items, so I wrote my own very simple lexer for this specific case (just plug in your own "stringtoparse" and you will get as output list: 'items')

#This lexer takes a JSON-like 'array' string and converts single-quoted array items into escaped double-quoted items,
#then puts the 'array' into a python list
#Issues such as  ["item 1", '","item 2 including those double quotes":"', "item 3"] are resolved with this lexer
items = []      #List of lexed items
item = ""       #Current item container
dq = True       #Double-quotes active (False->single quotes active)
bs = 0          #backslash counter
in_item = False #True if currently lexing an item within the quotes (False if outside the quotes; ie comma and whitespace)
for c in stringtoparse[1:-1]:   #Assuming encasement by brackets
    if c=="\\": #if there are backslashes, count them! Odd numbers escape the quotes...
        bs = bs + 1
        continue                    
    if (dq and c=='"') or (not dq and c=="'"):  #quote matched at start/end of an item
        if bs & 1==1:   #if escaped quote, ignore as it must be part of the item
            continue
        else:   #not escaped quote - toggle in_item
            in_item = not in_item
            if item!="":            #if item not empty, we must be at the end
                items += [item]     #so add it to the list of items
                item = ""           #and reset for the next item
            continue                
    if not in_item: #toggle of single/double quotes to enclose items
        if dq and c=="'":
            dq = False
            in_item = True
        elif not dq and c=='"':
            dq = True
            in_item = True
        continue
    if in_item: #character is part of an item, append it to the item
        if not dq and c=='"':           #if we are using single quotes
            item += bs * "\\" + "\""    #escape double quotes for JSON
        else:
            item += bs * "\\" + c
        bs = 0
        continue

Hopefully it is useful to somebody. Enjoy!

You can dump JSON with double quote by:

import json

# mixing single and double quotes
data = {'jsonKey': 'jsonValue',"title": "hello world"}

# get string with all double quotes
json_string = json.dumps(data) 

Two issues with answers given so far, if , for instance, one streams such non-standard JSON. Because then one might have to interpret an incoming string (not a python dictionary).

Issue 1 - demjson: With Python 3.7.+ and using conda I wasn't able to install demjson since obviosly it does not support Python >3.5 currently. So I need a solution with simpler means, for instance astand/or json.dumps.

Issue 2 - ast & json.dumps: If a JSON is both single quoted and contains a string in at least one value, which in turn contains single quotes, the only simple yet practical solution I have found is applying both:

In the following example we assume line is the incoming JSON string object :

>>> line = str({'abc':'008565','name':'xyz','description':'can control TV\'s and more'})

Step 1: convert the incoming string into a dictionary using ast.literal_eval()
Step 2: apply json.dumps to it for the reliable conversion of keys and values, but without touching the contents of values:

>>> import ast
>>> import json
>>> print(json.dumps(ast.literal_eval(line)))
{"abc": "008565", "name": "xyz", "description": "can control TV's and more"}

json.dumps alone would not do the job because it does not interpret the JSON, but only see the string. Similar for ast.literal_eval(): although it interprets correctly the JSON (dictionary), it does not convert what we need.

You can fix it that way:

s = "{'username':'dfdsfdsf'}"
j = eval(s)

import ast 
answer = subprocess.check_output(PYTHON_ + command, shell=True).strip()
    print(ast.literal_eval(answer.decode(UTF_)))

Works for me

demjson is also a good package to solve the problem of bad json syntax:

pip install demjson

Usage:

from demjson import decode
bad_json = "{'username':'dfdsfdsf'}"
python_dict = decode(bad_json)

Edit:

demjson.decode is a great tool for damaged json, but when you are dealing with big amourt of json data ast.literal_eval is a better match and much faster.

import json
data = json.dumps(list)
print(data)

The above code snippet should work.

you can use ast.literal_eval()

>>> import ast
>>> s = "{'username':'dfdsfdsf'}"
>>> ast.literal_eval(s)
{'username': 'dfdsfdsf'}

As said, JSON is not Python syntax. You need to use double quotes in JSON. Its creator is (in-)famous for using strict subsets of allowable syntax to ease programmer cognitive overload.

Below can fail if one of the JSON strings itself contains a single quote as pointed out by @Jiaaro. DO NOT USE. Left here as an example of what does not work.

It is really useful to know that there are no single quotes in a JSON string. Say, you copied and pasted it from a browser console/whatever. Then, you can just type

a = json.loads('very_long_json_string_pasted_here')

This might otherwise break if it used single quotes, too.

It truly solved my problem using eval function.

single_quoted_dict_in_string = "{'key':'value', 'key2': 'value2'}"
desired_double_quoted_dict = eval(single_quoted_dict_in_string)
# Go ahead, now you can convert it into json easily
print(desired_double_quoted_dict)