What is the difference between json.load() and json.loads() functions

Question

In Python, what is the difference between json.load() and json.loads()?

I guess that the load() function must be used with a file

Answer 1

In python3.7.7, the definition of json.load is as below according to cpython source code:

def load(fp, *, cls=None, object_hook=None, parse_float=None,
        parse_int=None, parse_constant=None, object_pairs_hook=None, **kw):

    return loads(fp.read(),
        cls=cls, object_hook=object_hook,
        parse_float=parse_float, parse_int=parse_int,
        parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)

json.load actually calls json.loads and use fp.read() as the first argument.

So if your code is:

with open (file) as fp:
    s = fp.read()
    json.loads(s)

It's the same to do this:

with open (file) as fp:
    json.load(fp)

But if you need to specify the bytes reading from the file as like fp.read(10) or the string/bytes you want to deserialize is not from file, you should use json.loads()

As for json.loads(), it not only deserialize string but also bytes. If s is bytes or bytearray, it will be decoded to string first. You can also find it in the source code.

def loads(s, *, encoding=None, cls=None, object_hook=None, parse_float=None,
        parse_int=None, parse_constant=None, object_pairs_hook=None, **kw):
    """Deserialize ``s`` (a ``str``, ``bytes`` or ``bytearray`` instance
    containing a JSON document) to a Python object.

    ...

    """
    if isinstance(s, str):
        if s.startswith('\ufeff'):
            raise JSONDecodeError("Unexpected UTF-8 BOM (decode using utf-8-sig)",
                                  s, 0)
    else:
        if not isinstance(s, (bytes, bytearray)):
            raise TypeError(f'the JSON object must be str, bytes or bytearray, '
                            f'not {s.__class__.__name__}')
        s = s.decode(detect_encoding(s), 'surrogatepass')