Myujth

When I try to load "foo.com" I get an exception, as expected; however, if I am loading a string containing a float number, it works. Just trying to figure out why this is the case.

$ python3
Python 3.6.5 (default, Jun 17 2018, 12:13:06)
[GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import json
>>> j = json.loads("foo.com")
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "/usr/local/Cellar/python/3.6.5_1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/__init__.py", line 354, in loads
 return _default_decoder.decode(s)
 File "/usr/local/Cellar/python/3.6.5_1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/decoder.py", line 339, in decode
 obj, end = self.raw_decode(s, idx=_w(s, 0).end())
 File "/usr/local/Cellar/python/3.6.5_1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/decoder.py", line 357, in raw_decode
 raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
>>> j = json.loads("123.6")
>>>

Quote from RFC7159 that defines JSON:

These are the six structural characters:

 begin-array = ws %x5B ws ; [ left square bracket
 begin-object = ws %x7B ws ; left curly bracket
 end-array = ws %x5D ws ; ] right square bracket
 end-object = ws %x7D ws ; right curly bracket
 name-separator = ws %x3A ws ; : colon
 value-separator = ws %x2C ws ; , comma

A JSON value MUST be an object, array, number, or string, or one of
the following three literal names:

false null true

<...> No other literal names are allowed.

value = false / null / true / object / array / number / string
object = begin-object [ member *( value-separator member ) ]
 end-object
array = begin-array [ value *( value-separator value ) ] end-array
number = [ minus ] int [ frac ] [ exp ]
string = quotation-mark *char quotation-mark

As you can see, the input foo.com does not satisfy any of that:

• it doesn't start with a begin-object
  


• nor does it start with a begin-array
  


• nor is it a number


• nor is it a string, because it does not start with a quotation-mark
  

However, 123.6 is a number:

123 . 6 == int frac

where, as per the RFC:

frac = decimal-point 1*DIGIT
int = zero / ( digit1-9 *DIGIT )

Thus, 123 . 6 is a value, so it's fine.

json.loads expects a string. When the JSON parser handles this string all is left is foo.com which is an invalid token. It's an edge case of this example:

json.loads('a: 1')

You would not expect this to work, wouldn't you? a is an invalid token.

For this to work we will need another set of quotes:

print(json.loads('"foo.com"'))
# foo.com