Python Gotcha's?

[Steven D'Aprano]

On Thu, 05 Apr 2012 11:06:11 +0000, Duncan Booth wrote:

> Steven D'Aprano <steve+comp.lang.python at pearwood.info> wrote:
> 
>> JSON expects double-quote marks, not single:
>>     v = json.loads("{'test':'test'}")  fails v =
>>     json.loads('{"test":"test"}')  succeeds
>> 
>> 
> You mean JSON expects a string with valid JSON? Quelle surprise.

No. The surprise is that there exists a tool invented in the 21st century 
that makes a distinction between strings quoted with " and  those quoted 
with '. Being used to a sensible language like Python, it boggled my 
brain the first time I tried to write some JSON and naturally treated the 
choice of quote mark as arbitrary. It especially boggled my brain when I 
saw the pathetically useless error message generated:

py> json.loads("{'test':'test'}")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.2/json/__init__.py", line 307, in loads
    return _default_decoder.decode(s)
  File "/usr/local/lib/python3.2/json/decoder.py", line 351, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/local/lib/python3.2/json/decoder.py", line 367, in raw_decode
    obj, end = self.scan_once(s, idx)
ValueError: Expecting property name: line 1 column 1 (char 1)

"Expecting property name"??? WTF???


The reason this is a Gotcha rather than a bug is because the JSON 
standard specifies the behaviour (probably in order to be compatible with 
Javascript). Hence, although the behaviour is mind-numbingly stupid, it 
is deliberate and not a bug. Hence, a gotcha.



-- 
Steven