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GeezerVison is showing docs.python.org — json — JSON encoder and decoder
|
JSON |
Python |
|---|---|
object |
dict |
array |
list |
string |
str |
number (int) |
int |
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.
object_hook is an optional function that will be called with the result of
every JSON object decoded and its return value will be used in place of the
given dict. This can be used to provide custom deserializations
(e.g. to support JSON-RPC class hinting).
object_pairs_hook is an optional function that will be called with the
result of every JSON object decoded with an ordered list of pairs. The
return value of object_pairs_hook will be used instead of the
dict. This feature can be used to implement custom decoders. If
object_hook is also defined, the object_pairs_hook takes priority.
Changed in version 3.1: Added support for object_pairs_hook.
parse_float is an optional function that 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. decimal.Decimal).
parse_int is an optional function that will be called with 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. float).
parse_constant is an optional function that will be called with one of the
following strings: '-Infinity', 'Infinity', 'NaN'. This can be
used to raise an exception if invalid JSON numbers are encountered.
If strict is false (True is the default), then control characters
will be allowed inside strings. Control characters in this context are
those with character codes in the 0–31 range, including '\t' (tab),
'\n', '\r' and '\0'.
If the data being deserialized is not a valid JSON document, a
JSONDecodeError will be raised.
Changed in version 3.6: All parameters are now keyword-only.
Return the Python representation of s (a str instance
containing a JSON document).
JSONDecodeError will be raised if the given JSON document is not
valid.
Extensible JSON encoder for Python data structures.
Supports the following objects and types by default:
Python |
JSON |
|---|---|
dict |
object |
list, tuple |
array |
str |
string |
int, float, int- & float-derived Enums |
number |
True |
true |
False |
false |
None |
null |
Changed in version 3.4: Added support for int- and float-derived Enum classes.
To extend this to recognize other objects, subclass and implement a
default() method with another method that returns a serializable object
for o if possible, otherwise it should call the superclass implementation
(to raise TypeError).
If skipkeys is false (the default), a TypeError will be raised when
trying to encode keys that are not str, int, float,
bool or None. If skipkeys is true, such items are simply skipped.
If ensure_ascii is true (the default), the output is guaranteed to have all incoming non-ASCII characters escaped. If ensure_ascii is false, these characters will be output as-is.
If check_circular is true (the default), then lists, dicts, and custom
encoded objects will be checked for circular references during encoding to
prevent an infinite recursion (which would cause a RecursionError).
Otherwise, no such check takes place.
If allow_nan is true (the default), then NaN, Infinity, and
-Infinity will be encoded as such. This behavior is not JSON
specification compliant, but is consistent with most JavaScript based
encoders and decoders. Otherwise, it will be a ValueError to encode
such floats.
If sort_keys is true (default: False), then the output of dictionaries
will be sorted by key; this is useful for regression tests to ensure that
JSON serializations can be compared on a day-to-day basis.
If indent is a non-negative integer or string, then JSON array elements and
object members will be pretty-printed with that indent level. An indent level
of 0, negative, or "" will only insert newlines. None (the default)
selects the most compact representation. Using a positive integer indent
indents that many spaces per level. If indent is a string (such as "\t"),
that string is used to indent each level.
Changed in version 3.2: Allow strings for indent in addition to integers.
If specified, separators should be an (item_separator, key_separator)
tuple. The default is (', ', ': ') if indent is None and
(',', ': ') otherwise. To get the most compact JSON representation,
you should specify (',', ':') to eliminate whitespace.
Changed in version 3.4: Use (',', ': ') as default if indent is not None.
If specified, default should be a function that gets called for objects that
can’t otherwise be serialized. It should return a JSON encodable version of
the object or raise a TypeError. If not specified, TypeError
is raised.
Changed in version 3.6: All parameters are now keyword-only.
Implement this method in a subclass such that it returns a serializable
object for o, or calls the base implementation (to raise a
TypeError).
For example, to support arbitrary iterators, you could implement
default() like this:
def default(self, o): try: iterable = iter(o) except TypeError: pass else: return list(iterable) # Let the base class default method raise the TypeError return super().default(o)
Return a JSON string representation of a Python data structure, o. For example:
>>> json.JSONEncoder().encode({"foo": ["bar", "baz"]}) '{"foo": ["bar", "baz"]}'
Encode the given object, o, and yield each string representation as available. For example:
for chunk in json.JSONEncoder().iterencode(bigobject): mysocket.write(chunk)
Subclass of ValueError with the following additional attributes:
The unformatted error message.
The JSON document being parsed.
The start index of doc where parsing failed.
The line corresponding to pos.
The column corresponding to pos.
Added in version 3.5.
The JSON format is specified by RFC 7159 and by
ECMA-404.
This section details this module’s level of compliance with the RFC.
For simplicity, JSONEncoder and JSONDecoder subclasses, and
parameters other than those explicitly mentioned, are not considered.
This module does not comply with the RFC in a strict fashion, implementing some extensions that are valid JavaScript but not valid JSON. In particular:
Infinite and NaN number values are accepted and output;
Repeated names within an object are accepted, and only the value of the last name-value pair is used.
Since the RFC permits RFC-compliant parsers to accept input texts that are not RFC-compliant, this module’s deserializer is technically RFC-compliant under default settings.
The RFC requires that JSON be represented using either UTF-8, UTF-16, or UTF-32, with UTF-8 being the recommended default for maximum interoperability.
As permitted, though not required, by the RFC, this module’s serializer sets ensure_ascii=True by default, thus escaping the output so that the resulting strings only contain ASCII characters.
Other than the ensure_ascii parameter, this module is defined strictly in
terms of conversion between Python objects and
Unicode strings, and thus does not otherwise directly address
the issue of character encodings.
The RFC prohibits adding a byte order mark (BOM) to the start of a JSON text,
and this module’s serializer does not add a BOM to its output.
The RFC permits, but does not require, JSON deserializers to ignore an initial
BOM in their input. This module’s deserializer raises a ValueError
when an initial BOM is present.
The RFC does not explicitly forbid JSON strings which contain byte sequences
that don’t correspond to valid Unicode characters (e.g. unpaired UTF-16
surrogates), but it does note that they may cause interoperability problems.
By default, this module accepts and outputs (when present in the original
str) code points for such sequences.
The RFC does not permit the representation of infinite or NaN number values.
Despite that, by default, this module accepts and outputs Infinity,
-Infinity, and NaN as if they were valid JSON number literal values:
>>> # Neither of these calls raises an exception, but the results are not valid JSON >>> json.dumps(float('-inf')) '-Infinity' >>> json.dumps(float('nan')) 'NaN' >>> # Same when deserializing >>> json.loads('-Infinity') -inf >>> json.loads('NaN') nan
In the serializer, the allow_nan parameter can be used to alter this behavior. In the deserializer, the parse_constant parameter can be used to alter this behavior.
The RFC specifies that the names within a JSON object should be unique, but does not mandate how repeated names in JSON objects should be handled. By default, this module does not raise an exception; instead, it ignores all but the last name-value pair for a given name:
>>> weird_json = '{"x": 1, "x": 2, "x": 3}' >>> json.loads(weird_json) {'x': 3}
The object_pairs_hook parameter can be used to alter this behavior.
The old version of JSON specified by the obsolete RFC 4627 required that
the top-level value of a JSON text must be either a JSON object or array
(Python dict or list), and could not be a JSON null,
boolean, number, or string value. RFC 7159 removed that restriction, and
this module does not and has never implemented that restriction in either its
serializer or its deserializer.
Regardless, for maximum interoperability, you may wish to voluntarily adhere to the restriction yourself.
Some JSON deserializer implementations may set limits on:
the size of accepted JSON texts
the maximum level of nesting of JSON objects and arrays
the range and precision of JSON numbers
the content and maximum length of JSON strings
This module does not impose any such limits beyond those of the relevant Python datatypes themselves or the Python interpreter itself.
When serializing to JSON, beware any such limitations in applications that may
consume your JSON. In particular, it is common for JSON numbers to be
deserialized into IEEE 754 double precision numbers and thus subject to that
representation’s range and precision limitations. This is especially relevant
when serializing Python int values of extremely large magnitude, or
when serializing instances of “exotic” numerical types such as
decimal.Decimal.
Source code: Lib/json/tool.py
The json.tool module provides a simple command line interface to validate
and pretty-print JSON objects.
If the optional infile and outfile arguments are not
specified, sys.stdin and sys.stdout will be used respectively:
$ echo '{"json": "obj"}' | python -m json.tool { "json": "obj" } $ echo '{1.2:3.4}' | python -m json.tool Expecting property name enclosed in double quotes: line 1 column 2 (char 1)
Changed in version 3.5: The output is now in the same order as the input. Use the
--sort-keys option to sort the output of dictionaries
alphabetically by key.
The JSON file to be validated or pretty-printed:
$ python -m json.tool mp_films.json [ { "title": "And Now for Something Completely Different", "year": 1971 }, { "title": "Monty Python and the Holy Grail", "year": 1975 } ]
If infile is not specified, read from sys.stdin.
Write the output of the infile to the given outfile. Otherwise, write it
to sys.stdout.
Sort the output of dictionaries alphabetically by key.
Added in version 3.5.
Disable escaping of non-ascii characters, see json.dumps() for more information.
Added in version 3.9.
Parse every input line as separate JSON object.
Added in version 3.8.
Mutually exclusive options for whitespace control.
Added in version 3.9.
Show the help message.
Footnotes