:mod:`dirtyjson` --- JSON decoder
.. module:: dirtyjson :synopsis: Decode JSON data from dirty files.
.. moduleauthor:: Scott Maxwell <scott@codecobblers.com>
JSON (JavaScript Object Notation) <http://json.org> is a subset of JavaScript syntax (ECMA-262 3rd edition) used as a lightweight data interchange format.
:mod:`dirtyjson` is a JSON decoder meant for extracting JSON-type data from .js files. The returned data structure includes information about line and column numbers, so you can output more useful error messages. The input can also include single quotes, line comments, inline comments, dangling commas, unquoted single-word keys, and hexadecimal and octal numbers.
The goal of :mod:`dirtyjson` is to read JSON objects out of files that are littered with elements that do not fit the official JSON standard. By providing line and column number contexts, a dirty JSON file can be used as source input for a complex data parser or compiler.
:mod:`dirtyjson` exposes an API familiar to users of the standard library :mod:`marshal` and :mod:`pickle` modules. However, :mod:`dirtyjson` provides only the load(s) capability. To write JSON, use either the standard :mod:`json` library or :mod:`simplejson`.
Note
The code for :mod:`dirtyjson` is a fairly drastically rewritten version of the loader in :mod:`simplejson` so thanks go to Bob Ippolito of the :mod:`simplejson` project for providing such a nice starting point.
Development of dirtyjson happens on Github: https://github.com/codecobblers/dirtyjson
Decoding JSON and getting position information:
>>> import dirtyjson
>>> obj = [u'foo', {u'bar': [u'baz', None, 1.0, 2]}]
>>> d = dirtyjson.loads("""["foo", /* not fu*/ {bar: ['baz', null, 1.0, 2,]}] and then ignore this junk""")
>>> d == obj
True
>>> pos = d.attributes(0) # line/column position of first element in array
>>> pos.line == 1
True
>>> pos.column == 2
True
>>> pos = d[1].attributes('bar') # line/column position of 'bar' key/value pair
>>> pos.key.line == 1
True
>>> pos.key.column == 22
True
>>> pos.value.line == 1
True
>>> pos.value.column == 27
True
Decoding unicode from JSON:
>>> dirtyjson.loads('"\\"foo\\bar"') == u'"foo\x08ar'
True
Decoding JSON from streams:
>>> from dirtyjson.compat import StringIO
>>> io = StringIO('["streaming API"]')
>>> dirtyjson.load(io)[0] == 'streaming API'
True
Using Decimal instead of float:
>>> import dirtyjson
>>> from decimal import Decimal
>>> dirtyjson.loads('1.1', parse_float=Decimal) == Decimal('1.1')
True
.. function:: load(fp[, encoding[, parse_float[, parse_int[, parse_constant[, search_for_first_object]]]]])
Performs the following translations in decoding by default:
+---------------+-------------------------+
| JSON | Python |
+===============+=========================+
| object | :class:`AttributedDict` |
+---------------+-------------------------+
| array | :class:`AttributedList` |
+---------------+-------------------------+
| string | unicode |
+---------------+-------------------------+
| number (int) | int, long |
+---------------+-------------------------+
| number (real) | float |
+---------------+-------------------------+
| true | True |
+---------------+-------------------------+
| false | False |
+---------------+-------------------------+
| null | None |
+---------------+-------------------------+
It also understands ``NaN``, ``Infinity``, and ``-Infinity`` as their
corresponding ``float`` values, which is outside the JSON spec.
Deserialize *fp* (a ``.read()``-supporting file-like object containing a JSON
document) to a Python object. :exc:`dirtyjson.Error` will be
raised if the given document is not valid.
If the contents of *fp* are encoded with an ASCII based encoding other than
UTF-8 (e.g. latin-1), then an appropriate *encoding* name must be specified.
Encodings that are not ASCII based (such as UCS-2) are not allowed, and
should be wrapped with ``codecs.getreader(fp)(encoding)``, or simply decoded
to a :class:`unicode` object and passed to :func:`loads`. The default
setting of ``'utf-8'`` is fastest and should be using whenever possible.
If *fp.read()* returns :class:`str` then decoded JSON strings that contain
only ASCII characters may be parsed as :class:`str` for performance and
memory reasons. If your code expects only :class:`unicode` the appropriate
solution is to wrap fp with a reader as demonstrated above.
*parse_float*, if specified, will be called with the string of every JSON
float to be decoded. By default, this is equivalent to ``float(num_str)``.
This can be used to use another datatype or parser for JSON floats
(e.g. :class:`decimal.Decimal`).
*parse_int*, if specified, will be called with the int of the string of every
JSON int to be decoded. By default, this is equivalent to ``int(num_str)``.
This can be used to use another datatype or parser for JSON integers
(e.g. :class:`float`).
.. note::
Unlike the standard :mod:`json` module, :mod:`dirtyjson` always does
``int(num_str, 0)`` before passing through to the converter passed is as
the *parse_int* parameter. This is to enable automatic handling of hex
and octal numbers.
*parse_constant*, if specified, will be called with one of the following
strings: ``true``, ``false``, ``null``, ``'-Infinity'``, ``'Infinity'``,
``'NaN'``. This can be used to raise an exception if invalid JSON numbers are
encountered or to provide alternate values for any of these constants.
*search_for_first_object*, if ``True``, will cause the parser to search for
the first occurrence of either ``{`` or ``[``. This is very useful for
reading an object from a JavaScript file.
.. function:: loads(s[, encoding[, parse_float[, parse_int[, parse_constant[, search_for_first_object[, start_index]]]]]) Deserialize *s* (a :class:`str` or :class:`unicode` instance containing a JSON document) to a Python object. :exc:`dirtyjson.Error` will be raised if the given JSON document is not valid. If *s* is a :class:`str` instance and is encoded with an ASCII based encoding other than UTF-8 (e.g. latin-1), then an appropriate *encoding* name must be specified. Encodings that are not ASCII based (such as UCS-2) are not allowed and should be decoded to :class:`unicode` first. If *s* is a :class:`str` then decoded JSON strings that contain only ASCII characters may be parsed as :class:`str` for performance and memory reasons. If your code expects only :class:`unicode` the appropriate solution is decode *s* to :class:`unicode` prior to calling loads. *start_index*, if non-zero, will cause the parser to start processing from the specified offset, while maintaining the correct line and column numbers. This is very useful for reading an object from the middle of a JavaScript file. The other arguments have the same meaning as in :func:`load`.
.. exception:: dirtyjson.Error(msg, doc, pos)
Subclass of :exc:`ValueError` with the following additional attributes:
.. attribute:: msg
The unformatted error message
.. attribute:: doc
The JSON document being parsed
.. attribute:: pos
The start index of doc where parsing failed
.. attribute:: lineno
The line corresponding to pos
.. attribute:: colno
The column corresponding to pos
The :mod:`dirtyjson` module uses :class:`AttributedDict` and
:class:`AttributedList` instead of dict and list. Each is actually a
subclass of its base type (dict or list) and can be used as if they were
the standard class, but these have been enhanced to store attributes with each
element. We use those attributes to store line and column numbers. You can use
that information to refer users back to the exact location in the original
source file.
This is a very simple utility class that contains line and column.
It is used for storing the position attributes for :class:`AttributedList`
and :class:`KeyValuePosition`
This is another very simple utility class that contains key and
value. Each of those is a :class:`Position` object specifying the
location in the original source string/file of the key and value. It is used
for storing the position attributes for :class:`AttributedDict`.
A subclass of dict that behaves exactly like a dict except that it
maintains order like an OrderedDict and allows storing attributes for
each key/value pair.
.. method:: add_with_attributes(self, key, value, attributes) Set the *key* in the underlying ``dict`` to the *value* and also store whatever is passed in as *attributes* for later retrieval. In our case, we store :class:`KeyValuePosition`.
.. method:: attributes(self, key)
Return the attributes associated with the specified *key* or ``None`` if
no attributes exist for the key. In our case, we store
:class:`KeyValuePosition`. Retrieve position info like this::
pos = d.attributes(key)
key_line = pos.key.line
key_column = pos.key.column
value_line = pos.value.line
value_column = pos.value.column
A subclass of list that behaves exactly like a list except that it
allows storing attributes for each value.
.. method:: append(self, value, attributes=None): Appends *value* to the list and *attributes* to the associated location. In our case, we store :class:`Position`.
.. method:: attributes(self, index)
Returns the attributes for the value at the given *index*. In our case,
we store :class:`Position`. Retrieve position info like this::
pos = l.attributes(index)
value_line = pos.line
value_column = pos.column
Note
This class is NOT robust. If you insert or delete items, the attributes will get out of sync. Making this a non-naive class would be a nice enhancement.