In Python, what is the difference between json.load() and json.loads()?
I guess that the load() function must be used with a file object (I need thus to use a context manager) while the loads() function take the path to the file as a string. It is a bit confusing.
Does the letter “s” in json.loads() stand for string?
Thanks a lot for your answers!
Answers:
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Method 1
Yes, s stands for string. The json.loads function does not take the file path, but the file contents as a string. Look at the documentation.
Method 2
Just going to add a simple example to what everyone has explained,
json.load()
json.load can deserialize a file itself i.e. it accepts a file object, for example,
# open a json file for reading and print content using json.load
with open("/xyz/json_data.json", "r") as content:
print(json.load(content))
will output,
{u'event': {u'id': u'5206c7e2-da67-42da-9341-6ea403c632c7', u'name': u'Sufiyan Ghori'}}
If I use json.loads to open a file instead,
# you cannot use json.loads on file object
with open("json_data.json", "r") as content:
print(json.loads(content))
I would get this error:
TypeError: expected string or buffer
json.loads()
json.loads() deserialize string.
So in order to use json.loads I will have to pass the content of the file using read() function, for example,
using content.read() with json.loads() return content of the file,
with open("json_data.json", "r") as content:
print(json.loads(content.read()))
Output,
{u'event': {u'id': u'5206c7e2-da67-42da-9341-6ea403c632c7', u'name': u'Sufiyan Ghori'}}
That’s because type of content.read() is string, i.e. <type 'str'>
If I use json.load() with content.read(), I will get error,
with open("json_data.json", "r") as content:
print(json.load(content.read()))
Gives,
AttributeError: ‘str’ object has no attribute ‘read’
So, now you know json.load deserialze file and json.loads deserialize a string.
Another example,
sys.stdin return file object, so if i do print(json.load(sys.stdin)), I will get actual json data,
cat json_data.json | ./test.py
{u'event': {u'id': u'5206c7e2-da67-42da-9341-6ea403c632c7', u'name': u'Sufiyan Ghori'}}
If I want to use json.loads(), I would do print(json.loads(sys.stdin.read())) instead.
Method 3
Documentation is quite clear: https://docs.python.org/2/library/json.html
json.load(fp[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, **kw]]]]]]]])
Deserialize fp (a .read()-supporting file-like object containing a
JSON document) to a Python object using this conversion table.
json.loads(s[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, **kw]]]]]]]])
Deserialize s (a str or unicode instance containing a JSON document)
to a Python object using this conversion table.
So load is for a file, loads for a string
Method 4
QUICK ANSWER (very simplified!)
json.load() takes a FILE
json.load() expects a file (file object) – e.g. a file you opened before given by filepath like
'files/example.json'.
json.loads() takes a STRING
json.loads() expects a (valid) JSON string – i.e.
{"foo": "bar"}
EXAMPLES
Assuming you have a file example.json with this content: { “key_1”: 1, “key_2”: “foo”, “Key_3”: null }
>>> import json
>>> file = open("example.json")
>>> type(file)
<class '_io.TextIOWrapper'>
>>> file
<_io.TextIOWrapper name='example.json' mode='r' encoding='UTF-8'>
>>> json.load(file)
{'key_1': 1, 'key_2': 'foo', 'Key_3': None}
>>> json.loads(file)
Traceback (most recent call last):
File "/usr/local/python/Versions/3.7/lib/python3.7/json/__init__.py", line 341, in loads
TypeError: the JSON object must be str, bytes or bytearray, not TextIOWrapper
>>> string = '{"foo": "bar"}'
>>> type(string)
<class 'str'>
>>> string
'{"foo": "bar"}'
>>> json.loads(string)
{'foo': 'bar'}
>>> json.load(string)
Traceback (most recent call last):
File "/usr/local/python/Versions/3.7/lib/python3.7/json/__init__.py", line 293, in load
return loads(fp.read(),
AttributeError: 'str' object has no attribute 'read'
Method 5
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')
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