向现有 JSON 文件添加值

Question

I would like to define the following simple function:

def add_to_json(self, json, node_name, value_name, value):
    json[node_name][value_name] = value

where json is a JSON file to modify, so it would be called like this:

jsonToModify = json.load(open(path_to_jason_file)) # path is of the type: "C:/Users/path/to/file.json"
self.add_to_json(jsonToModify, "NodeName", "ValueName", self.stuff)

I have searched how to use the json.load() function, but I get this error if I give it a string:

I am not sure on what to give to json.load ; how can I give the path to my file as an input?

Answer 1

Here is a demo of reading data from an existing json file into a Python object (a dict), adding a value to the dict and writing the updated dict as json back to the file. It's cut and paste from an IPython session running Python 2.7.10.

!type test.json # prints the contents of the file test.json
{"a": [1, 3, "X", true], "b": {"hello": "world"}}

import json

with open("test.json") as json_file:
    data = json.load(json_file)
    print(data)

{u'a': [1, 3, u'X', True], u'b': {u'hello': u'world'}}

data['c'] = 'data_received' # add key: value to data

with open('test.json', 'w') as outfile:
    json.dump(data, outfile)

!type test.json # shows file contents have been updated 
{"a": [1, 3, "X", true], "c": "data_received", "b": {"hello": "world"}}

Putting all this into a function, here is a version of add_to_json:

import json
import sys

def add_to_json(json_file, node_name, value_name, value):
    update = False
    data = {}
    try:
        with open(json_file) as f:
            data = json.load(f)
    except:
        print 'opening/loading',json_file,'failed:',sys.exc_info()[0]
        return False
    if node_name in data:
        if isinstance(data[node_name],dict):
            data[node_name][value_name] = value
            update = True
        elif isinstance(data[node_name],list):
            data[node_name].append(value)
            update = True
        else:
            print value,'not added to',node_name,'since its not a list or dict'
    else: # add node_name as dict
        data[node_name] = {value_name: value}
        update = True
    if update:
        try:
            with open(json_file, 'w') as f:
                json.dump(data, f)
            print json_file,'has been updated'
            return True
        except:
            print 'writing',json_file,'failed:',sys.exc_info()[0]
            return False


!type test2.json
{"a": [1, 3, "X", true], "n": {"y": 2, "x": 1}, "e": {}, "f": []}

add_to_json('test2.json', 'n', 'z', 1)
test2.json has been updated
Out[5]: True

!type test2.json
{"a": [1, 3, "X", true], "f": [], "e": {}, "n": {"y": 2, "x": 1, "z": 1}}

add_to_json('test2.json', 'a', None, 25)
test2.json has been updated
Out[7]: True

!type test2.json
{"a": [1, 3, "X", true, 25], "n": {"y": 2, "x": 1, "z": 1}, "e": {}, "f": []}

add_to_json('test2.json', 'e', 'new_key', 'new_value')
test2.json has been updated
Out[9]: True

!type test2.json
{"a": [1, 3, "X", true, 25], "f": [], "e": {"new_key": "new_value"}, "n": {"y": 2, "x": 1, "z": 1}}

add_to_json('test2.json', 'f', None, 37)
test2.json has been updated
Out[11]: True

!type test2.json
{"a": [1, 3, "X", true, 25], "n": {"y": 2, "x": 1, "z": 1}, "e": {"new_key": "new_value"}, "f": [37]}

add_to_json('test2.json', 'new_dict', 'zebra', 23)
test2.json has been updated
Out[13]: True

!type test2.json
{"a": [1, 3, "X", true, 25], "new_dict": {"zebra": 23}, "f": [37], "e": {"new_key": "new_value"}, "n": {"y": 2, "x": 1, "z": 1}}

add_to_json('nonexistent.json', 'new_dict', 'zebra', 47)
opening/loading nonexistent.json failed: <type 'exceptions.IOError'>
Out[15]: False