I'm trying to parse a json and keep getting ValueError. File reports the file as being "UTF-8 Unicode (with BOM) text", vim reports it as UTF-8, ...

json.load docs says it support UTF-8 out of the box.

Here's a link to the file : http://donnees.ville.sherbrooke.qc.ca/storage/f/2014-03-10T17%3A45%3A18.959Z/matieres-residuelles.json

In Python 2, json.loads() accepts str and unicode types. You can support JSON starting with a UTF-8 BOM using the Python codec "utf-8-sig". Example:

>>> codecs.BOM_UTF8 + b'{\n}'
'\xef\xbb\xbf{\n}'
>>> json.loads(codecs.BOM_UTF8 + b'{\n}')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/json/__init__.py", line 338, in loads
    return _default_decoder.decode(s)
  File "/usr/lib64/python2.7/json/decoder.py", line 365, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib64/python2.7/json/decoder.py", line 383, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded
>>> json.loads((codecs.BOM_UTF8 + b'{\n}').decode('utf-8-sig'))
{}

Currently json.load/loads don't support binary input. See bpo-17909 and bpo-19837.

The new JSON RFC now at least mentions BOM handling:
https://tools.ietf.org/html/rfc7159#section-8.1 :

Implementations MUST NOT add a byte order mark to the beginning of a
JSON text. In the interests of interoperability, implementations
that parse JSON texts MAY ignore the presence of a byte order mark
rather than treating it as an error.

I added code to skip the bom if present when encoding is either None or "utf-8". The problem I have with Victor's solution is that users don't know these files are not plain UTF-8. Most text editor says it's utf-8 encoded, how can a user figure out there 3 hidden bytes at the start of the file ?

Kristian

I think you should use codecs.BOM_UTF8 rather than using hardcoded string "\xef\xbb\xbf" directly.

And why special casing UTF-8 while we're at it? What about other encodings and their BOMs?

This issue is outdated since implementing automatic encoding detecting in bpo-17909.