Serialize obj to a JSON formatted str.
If skipkeys is false then dict keys that are not basic types (str, unicode, int, long, float, bool, None) will be skipped instead of raising a TypeError.
If ensure_ascii is false, then the return value will be a unicode instance subject to normal Python str to unicode coercion rules instead of being escaped to an ASCII str.
If check_circular is false, then the circular reference check for container types will be skipped and a circular reference will result in an OverflowError (or worse).
If allow_nan is false, then it will be a ValueError to serialize out of range float values (nan, inf, -inf) in strict compliance of the JSON specification, instead of using the JavaScript equivalents (NaN, Infinity, -Infinity).
If indent is a non-negative integer, then JSON array elements and object members will be pretty-printed with that indent level. An indent level of 0 will only insert newlines. None is the most compact representation.
If separators is an (item_separator, dict_separator) tuple then it will be used instead of the default (', ', ': ') separators. (',', ':') is the most compact JSON representation.
encoding is the character encoding for str instances, default is UTF-8.
default(obj) is a function that should return a serializable version of obj or raise TypeError. The default simply raises TypeError.
To use a custom JSONEncoder subclass (e.g. one that overrides the .default() method to serialize additional types), specify it with the cls kwarg; otherwise JSONEncoder is used.