ToJSon returns valid syntax for a JavaScript object, but it is not parseable 
with many JSON implementations 
because it uses syntax that is not within the subset defined by the JSON 
standard.

The simplest solution is probably to rename this function or at least document 
that it doesn't really return 
JSON, but expects to be executed by a full JS interpreter.

For example, the result will not parse with Python 2.6's json package:
>>> d = gviz_api.DataTable(('a', 'string'), ['foo'])
>>> d.ToJSon()
"{cols: [{id:'a',label:'a',type:'string'}],rows: [{c:[{v:'foo'}]}]}"
>>> json.loads(d.ToJSon())
Traceback (most recent call last):
...
ValueError: Expecting property name: line 1 column 1 (char 1)

Some more basic issues are:
- JSON strings must use double-quotes
- JSON keys must be quoted following the string syntax
e.g. {"key": "value"}, not {key: 'value'}

Python's default unicode escaping is also not compatible with JSON strings.  
For example, it will use \x hex 
escape codes which do happen to work in JavaScript, but JSON only allows \u 
4-digit hex escapes, e.g.
Wrong:
>>> json.loads('"\\xfc"')
Traceback (most recent call last):
...
ValueError: Invalid \escape: line 1 column 1 (char 1)

Right:
>>> json.loads('"\\u00fc"')
u'\xfc'

Also, JSON does not define any syntax for Date types, so the "new Date()" 
syntax is not supported by most 
non-JS-native JSON parsers.

Since this data structure is primarily designed for consumption by the JS viz 
API, I don't have a problem with 
the syntax remaining as it is, just please don't misrepresent it as "JSON", 
which could cause confusion if 
people try to parse it with a JSON library.