如何取回与 fileInfo 一起存储且没有转义序列的正确 json？

Question

我无法检索我存储在 Maya 的 json.dumps 中的

exact

JSON 字符串转储 (

fileInfo

)。

>>> import pymel.core as pc
>>> json.dumps({'foo': 123})
'{"foo": 123}'
>>> pc.fileInfo['foo'] = json.dumps({'foo': 123})
>>> pc.fileInfo['foo']
u'{\\"foo\\": 123}'
>>> json.loads(pc.fileInfo['foo']) # this produces an error because of the escape sequence
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "c:\Program Files\Autodesk\Maya2011\bin\python26.zip\json\__init__.py", line 307, in loads

  File "c:\Program Files\Autodesk\Maya2011\bin\python26.zip\json\decoder.py", line 319, in decode
  File "c:\Program Files\Autodesk\Maya2011\bin\python26.zip\json\decoder.py", line 336, in raw_decode
  File "c:\Program Files\Autodesk\Maya2011\bin\python26.zip\json\scanner.py", line 55, in iterscan
  File "c:\Program Files\Autodesk\Maya2011\bin\python26.zip\json\decoder.py", line 171, in JSONObject
ValueError: Expecting property name: line 1 column 1 (char 1)

问题是，当 Maya 存储值时，它会确保它被正确转义。但当检索到该字符串时，其格式错误为

json.loads

。我该如何解决这个问题？

我基本上寻找的是 unescapes MEL 在保存值时引入的转义序列？到目前为止，我还没有找到任何可以做到这一点的东西。

MEL 与 C 有很多相似之处，因此转义序列与 C 的转义序列基本相同，如上所示。

Answer 1

@theodox 的答案可能是正确的。但是如果你知道json字符串会被转义。您可以简单地使用以下命令取回字符串的原始未转义版本。

mystring.decode('unicode_escape')

因此在上述情况下，反序列化存储信息的正确方法是：

json.loads(pc.fileInfo['foo'].decode('unicode_escape'))

虽然它看起来有点难看，所以你可以将它放在一个函数中。

def safe_json_loads(str):
    return json.loads(str.decode('unicode_escape'))


data = safe_json_loads(pc.fileInfo['foo'])

干杯，

Answer 2

确保从 fileInfo 中完整获取内容的最佳方法是在传入时对其进行 Base64 编码，并在传出时对其进行解码。 Maya 不会为您执行此操作，并且正如您所见，它提供的转义很奇怪。

这是我使用的；它使用 yaml 但你应该能够交换 json 没有问题。我已经用它按照您想要的方式保存 yaml 数据。

'''
mayaPersist - namespace for functions related to storing data in fileInfo objects inside the current Maya file

I've tested this (a little) with as many as 100,000 integers - it works but it's slooow at that size
< 1000 values seems imperceptible
'''

import yaml
import base64
from  maya.cmds import fileInfo
import itertools

def save(key, value):
    '''
    save the specified value as a base64 encoded yaml dunp at key 'key'
    '''
    encoded =encode(value)
    fileInfo(key, encoded)

def load(key):
    '''
    return the value stored at 'key', or None if the value can't be found

    @note it is possible to store a 'None' in the value, so this doesn't prove that the key does not exist !
    '''
    answer = fileInfo(key, q=True)
    if not answer:
        return None
    return decode(answer[0])

def exists(key):
    '''
    returns true if the specified key exists
    '''
    answer = fileInfo(key, q=True)
    return len(answer) != 0

def ls():
    '''
    a generator that returns all of the key-value pairs in this file's fileInfo

    @note:  these are not decoded, because they contain a mix of native stirngs and b64 values
    '''
    all_values = fileInfo(q=True)
    keys = itertools.islice(all_values, 0, None, 2)
    values = itertools.islice(all_values, 1, None, 2)
    return itertools.izip(keys, values)


def delete(key):
    '''
    remove the key and any data stored with it from this file
    '''
    fileInfo(rm=key)

def decode(value):
    '''
    convert a base64'ed yaml object back into a maya object

    if the object is not encoded (eg, one of the default string values) return it untouched
    '''
    try:
        val = base64.b64decode(value)
        return yaml.load(val)
    except TypeError:  
        return value



def encode (value):
    '''
    return the supplied value encoded into base64-packed YAML dump
    '''
    return  base64.b64encode(yaml.dump(value))

Answer 3

遇到同样的问题，一旦从 fileInfo 命令获取字符串，只需替换转义的引号，如下所示：

# Lets say you stored some json data in a fileInfo called 'tester'
import maya.cmds as cmds
import json

s = cmds.fileInfo( 'tester', q = True )[ 0 ]
s = s.replace( '\\"', '"' ) # Handle escaped quotes
j = json.loads( s )
print( json.dumps( j, indent = 4 ) )