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@jdp /jsonform.py
Last active Aug 29, 2015

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quick and dirty implementation of HTML JSON form draft
# -*- coding: utf-8 -*-
import json
undefined = object()
class JSONFormEncoder(json.JSONEncoder):
def default(self, obj):
if obj == undefined:
return None
else:
return super(JSONFormEncoder, self).default(obj)
def parse_path(path):
"""
http://www.w3.org/TR/2014/WD-html-json-forms-20140529/#dfn-steps-to-parse-a-json-encoding-path
"""
original = path
failure = [(original, {'last': True, 'type': object})]
steps = []
try:
first_key = path[:path.index("[")]
if not first_key:
return original
steps.append((first_key, {'type': 'object'}))
path = path[path.index("["):]
except ValueError:
return failure
while path:
if path.startswith("[]"):
steps[-1][1]['append'] = True
path = path[2:]
if path:
return failure
elif path[0] == "[":
path = path[1:]
try:
key = path[:path.index("]")]
path = path[path.index("]")+1:]
except ValueError:
return failure
try:
steps.append((int(key), {'type': 'array'}))
except ValueError:
steps.append((key, {'type': 'object'}))
else:
return failure
for i in range(len(steps)-1):
steps[i][1]['type'] = steps[i+1][1]['type']
steps[-1][1]['last'] = True
return steps
def set_value(context, step, current_value, entry_value):
"""
http://www.w3.org/TR/2014/WD-html-json-forms-20140529/#dfn-steps-to-set-a-json-encoding-value
"""
key, flags = step
if flags.get('last', False):
if current_value == undefined:
if flags.get('append', False):
context[key] = [entry_value]
else:
if isinstance(context, list) and len(context) <= key:
context.extend([undefined] * (key - len(context) + 1))
context[key] = entry_value
elif isinstance(current_value, list):
context[key].append(entry_value)
elif isinstance(current_value, dict):
set_value(current_value, ("", {'last': True}), current_value.get("", undefined), entry_value)
else:
context[key] = [current_value, entry_value]
return context
else:
if current_value == undefined:
if flags.get('type') == 'array':
context[key] = []
else:
if isinstance(context, list) and len(context) <= key:
context.extend([undefined] * (key - len(context) + 1))
context[key] = {}
return context[key]
elif isinstance(current_value, dict):
return context[key]
elif isinstance(current_value, list):
if flags.get('type') == 'array':
return current_value
else:
obj = {}
for i, item in enumerate(current_value):
if item != undefined:
obj[i] = item
else:
context[key] = obj
return obj
else:
obj = {"": current_value}
context[key] = obj
return obj
def encode(pairs):
"""
The application/json form encoding algorithm.
http://www.w3.org/TR/2014/WD-html-json-forms-20140529/#the-application-json-encoding-algorithm
"""
result = {}
for key, value in pairs:
steps = parse_path(key)
context = result
for step in steps:
try:
current_value = context.get(step[0], undefined)
except AttributeError:
try:
current_value = context[step[0]]
except IndexError:
current_value = undefined
context = set_value(context, step, current_value, value)
return result
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