值错误：期望值

Question

I have a line of code from a Data Analysis Book using python.

return = [json.loads(line) for line in open(path)]

Path being the designated text file I have with JSON formatted text inside.

The link is here. https://raw.githubusercontent.com/pydata/pydata-book/master/ch02/usagov_bitly_data2012-03-16-1331923249.txt

ValueError                                Traceback (most recent call last)
<ipython-input-35-b1e0b494454a> in <module>()
----> 1 records = [json.loads(line) for line in open(path)]

<ipython-input-35-b1e0b494454a> in <listcomp>(.0)
----> 1 records = [json.loads(line) for line in open(path)]

/usr/lib/python3.4/json/__init__.py in loads(s, encoding, cls,    object_hook, parse_float, parse_int, parse_constant, object_pairs_hook, **kw)
316             parse_int is None and parse_float is None and
317             parse_constant is None and object_pairs_hook is None and not kw):
--> 318         return _default_decoder.decode(s)
319     if cls is None:
320         cls = JSONDecoder

/usr/lib/python3.4/json/decoder.py in decode(self, s, _w)
341 
342         """
--> 343         obj, end = self.raw_decode(s, idx=_w(s, 0).end())
344         end = _w(s, end).end()
345         if end != len(s):

/usr/lib/python3.4/json/decoder.py in raw_decode(self, s, idx)
359             obj, end = self.scan_once(s, idx)
360         except StopIteration as err:
--> 361             raise ValueError(errmsg("Expecting value", s, err.value)) from None
362         return obj, end

ValueError: Expecting value: line 2 column 1 (char 1)

Any help is appreciated.

Answer 1

as said in your trace back the value being returned is the None type. Null, theres nothing to return. Double check your source.

Answer 2

line 2 starts with

"a": "GoogleMaps\/RochesterNY",

Line 1 and the other lines start with

"a": "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.78 Safari/535.11",

It appears that the "a" key is supposed to be an indicator of the browser type and not the URL description. This would probably cause a problem when you are trying to decode it. I would suggest removing it from the data and seeing what happens.

Your call to

--> 343         obj, end = self.raw_decode(s, idx=_w(s, 0).end())

appears to be in error. Did you write your own version of raw_decode() as the Python JSON manual]( https://docs.python.org/3/library/json.html ) states that

raw_decode(s)

Decode a JSON document from s (a str beginning with a JSON document) and return a 2-tuple of the Python representation and the index in s where the document ended.

This can be used to decode a JSON document from a string that may have extraneous data at the end.

which means that ext is not a valid argument for the standard function. It is better to write your own function with a different name in order to prevent accidents in usage.

Similarly you would be better off writing your for loop

records = [json.loads(line) for line in open(path)]

as for line in open(path): records = [json.loads(line)

However, given that it appears that the exception is raised from the raw_decode, it would appear that the line that you are trying to decode contains an error. You should check the data that you are processing and handle the error or fix the data. Since it is a JSON line, you should be able to print the line to determine what the error is. It could be your code or the actual data line.