# jiter

[](https://github.com/pydantic/jiter/actions?query=event%3Apush+branch%3Amain+workflow%3ACI)
[](https://pypi.python.org/pypi/jiter)
[](https://github.com/pydantic/jiter)
[](https://github.com/pydantic/jiter/blob/main/LICENSE)

This is a standalone version of the JSON parser used in `pydantic-core`. The recommendation is to only use this package directly if you do not use `pydantic`.

The API is extremely minimal:

```python
def from_json(
json_data: bytes,
/,
*,
allow_inf_nan: bool = True,
cache_mode: Literal[True, False, "all", "keys", "none"] = "all",
partial_mode: Literal[True, False, "off", "on", "trailing-strings"] = False,
catch_duplicate_keys: bool = False,
float_mode: Literal["float", "decimal", "lossless-float"] = False,
) -> Any:
"""
Parse input bytes into a JSON object.

Arguments:
json_data: The JSON data to parse
allow_inf_nan: Whether to allow infinity (`Infinity` an `-Infinity`) and `NaN` values to float fields.
Defaults to True.
cache_mode: cache Python strings to improve performance at the cost of some memory usage
- True / 'all' - cache all strings
- 'keys' - cache only object keys
- False / 'none' - cache nothing
partial_mode: How to handle incomplete strings:
- False / 'off' - raise an exception if the input is incomplete
- True / 'on' - allow incomplete JSON but discard the last string if it is incomplete
- 'trailing-strings' - allow incomplete JSON, and include the last incomplete string in the output
catch_duplicate_keys: if True, raise an exception if objects contain the same key multiple times
float_mode: How to return floats: as a `float`, `Decimal` or `LosslessFloat`

Returns:
Python object built from the JSON input.
"""

def cache_clear() -> None:
"""
Reset the string cache.
"""

def cache_usage() -> int:
"""
get the size of the string cache.

Returns:
Size of the string cache in bytes.
"""
```
## Examples

The main function provided by Jiter is `from_json()`, which accepts a bytes object containing JSON and returns a Python dictionary, list or other value.

```python
import jiter

json_data = b'{"name": "John", "age": 30}'
parsed_data = jiter.from_json(json_data)
print(parsed_data) # Output: {'name': 'John', 'age': 30}
```

### Handling Partial JSON

Incomplete JSON objects can be parsed using the `partial_mode=` parameter.

```python
import jiter

partial_json = b'{"name": "John", "age": 30, "city": "New Yor'

# Raise error on incomplete JSON
try:
jiter.from_json(partial_json, partial_mode=False)
except ValueError as e:
print(f"Error: {e}")

# Parse incomplete JSON, discarding incomplete last field
result = jiter.from_json(partial_json, partial_mode=True)
print(result) # Output: {'name': 'John', 'age': 30}

# Parse incomplete JSON, including incomplete last field
result = jiter.from_json(partial_json, partial_mode='trailing-strings')
print(result) # Output: {'name': 'John', 'age': 30, 'city': 'New Yor'}
```

### Catching Duplicate Keys

The `catch_duplicate_keys=True` option can be used to raise a `ValueError` if an object contains duplicate keys.

```python
import jiter

json_with_dupes = b'{"foo": 1, "foo": 2}'

# Default behavior (last value wins)
result = jiter.from_json(json_with_dupes)
print(result) # Output: {'foo': 2}

# Catch duplicate keys
try:
jiter.from_json(json_with_dupes, catch_duplicate_keys=True)
except ValueError as e:
print(f"Error: {e}")
```



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