Not support json key start with "_"

[JFRabbit]

version: 0.3.3

code:

namedtupled.map({'_key': 1})

result:

Traceback (most recent call last):
  File "/Users/jasonzhang/Documents/xxxxxx.py", line 58, in <module>
    namedtupled.map({'_key': 1})
  File "/Users/jasonzhang/Documents/code/k2assets-data-generator/venv/lib/python3.7/site-packages/namedtupled/namedtupled.py", line 11, in mapper
    return namedtuple_wrapper(_nt_name, **mapping)
  File "/Users/jasonzhang/Documents/code/k2assets-data-generator/venv/lib/python3.7/site-packages/namedtupled/namedtupled.py", line 18, in namedtuple_wrapper
    wrap = namedtuple(_nt_name, kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/collections/__init__.py", line 370, in namedtuple
    raise ValueError('Field names cannot start with an underscore: '
ValueError: Field names cannot start with an underscore: '_key'

[awwwd]

Hmm. So the underlying data structure collections.namedtuple doesn't allow any field name starting with underscore. There is a keyword only parameter rename which is set to False by default. But, If set to True then that will rename the fields with the respective positional value.

>>> dummy = namedtuple('dummy', '_foo bar', rename=True)
>>> dummy._fields
('_0', 'bar')