API¶

Main Interface¶

class jsv.JSVReader(record_file, template_file=None)¶

Bases: jsv.template_io.JSVCollection

Context manager for reading data from files in JSV format.

This is the main class for reading JSV records from a file or stream. If either record_file or template_file is a string, then it must be used as a context manager. Otherwise, the context manager does nothing with the file pointers, and the object can be used directly.

All of the templates used by a JSVReader instance must come from either record_file or template_file. If it is present, template_file is read during initialization (if template_file is a file pointer) or when entering the context manager (if template_file is a file path).

Example

Take the file in.jsv which looks like this:

#_ {"key_1","key_2","key_3"}
{1,2,3}
{4,5,6}
{7,8,9}

We can then run the following code:

>>> with jsv.JSVReader('in.jsv') as r:
...     for obj in r:
...         print(obj)
...
{'key_1': 1, 'key_2': 2, 'key_3': 3}
{'key_1': 4, 'key_2': 5, 'key_3': 6}
{'key_1': 7, 'key_2': 8, 'key_3': 9}

Parameters:

record_file (filepath or io.TextIOBase) – Either a file path, or a file pointer from which records should be read. Templates, if present, will also be read.
template_file (filepath or io.TextIOBase) – Either a file path, or a file pointer to which templates should be written. If present, templates and records will be written to different files. By convention, records should use the file extension .jsvr and templates should use file extension .jsvt.

__iter__()¶

Iterator magic method for the reader object. Templates are consumed to decode records, but are not returned by the iterator.

Returns:	(object) where `object` is a json-compatible object representing a record.

items()¶

Iterator over both the values and the template ids for each record. Templates are consumed to decode records, but are not returned by the iterator.

Returns:	(tid, object) where `tid` is the id of the template used, and `object` is a json-compatible object.

class jsv.JSVWriter(record_file, record_mode='at', template_dict=None, template_file=None, template_mode='at')¶

Bases: jsv.template_io.JSVCollection

Context manager for writing data to files in JSV format.

This is the main class for writing JSV records to a file or stream. If either record_file or template_file is a string, then it must be used as a context manager. Otherwise, the context manager does nothing with the file pointers, and the object can be used as a context manager or not.

As JSVWriter inherits from JSVCollection, it maintains any templates assigned to it. In addition, templates are immediately written to the file or stream when added.

Example

>>> out = []
>>> out.append({'key_1': 1, 'key_2': 2, 'key_3': 3})
>>> out.append({'key_1': 4, 'key_2': 5, 'key_3': 6})
>>> out.append({'key_1': 7, 'key_2': 8, 'key_3': 9})
>>> with jsv.JSVWriter('out.jsv', 'wt', {'_': '{"key_1","key_2","key_3"}'}) as w:
...     for obj in out:
...         w.write(obj)

This creates the file out.jsv which looks like this:

#_ {"key_1","key_2","key_3"}
{1,2,3}
{4,5,6}
{7,8,9}

Parameters:

record_file (filepath or io.TextIOBase) – Either a file path, or a file pointer to which records should be written. If template_file is not given, templates will be written here as well.
record_mode (str) – file mode for the record file. Only used if record_file is a string.
template_dict (dict) – Dictionary of templates. See JSVCollection.
template_file (filepath or io.TextIOBase) – Either a file path, or a file pointer to which templates should be written. if present, templates and records will be written to different files. By convention, records should use the file extension .jsvr and templates should use file extension .jsvt.
template_mode (str) – file mode for the template file. Only used if template_file is a string.

write(obj, tid='_')¶

Writes an object to a file or stream in JSV format

Parameters:	obj (json-compatible object) – Object to be written. tid (str) – Id of the template used to encode `obj`.

class jsv.JSVCollection(template_dict=None)¶

Use multiple templates in a single data stream.

A JSVCollection object is an associative array of templates, each with an id of type str. This facilitates reading from and writing to a file or stream, as each line in the file or stream must be matched to a template.

Parameters:	template_dict (dict) – A dictionary whose keys are template ids and whose values are `JSVTemplate` objects, or are values suitable for the `JSVTemplate` constructor.

get_record_line(obj, tid='_')¶

Returns a string defining a record in a .jsv file. For example:

>>> coll = jsv.JSVCollection()
>>> coll['template_1'] = '{"key_1"}'
>>> coll.get_record_line({'key_1': 'value_1'}, 'template_1')
'@template_1 {"value_1"}'

Parameters:	obj (json-compatible object) – The object to be encoded. tid (str) – The id of the template.

get_template_line(tid='_')¶

Return a string defining a template in a .jsv file. For example:

>>> coll = jsv.JSVCollection()
>>> coll['template_1'] = '{"key_1"}'
>>> coll.get_template_line('template_1')
'#template_1 {"key_1"}'

Parameters:	tid (str) – The id of the template.

items()¶: Iterator that yields the tuple (tid, template).

read_line(line)¶

Used to read a single line from a .jsv file. For example:

>>> coll = jsv.JSVCollection()
>>> tid, tmpl = coll.read_line('#template_1 {"key_1"}')
>>> coll[tid] = tmpl
>>> coll.read_line('@template_1 {"value_1"}')
('template_1', {'key_1': 'value_1'})

Parameters:	line (str) – String to be read. The string should be in the format used by a `.jsv` file. It can be either a record or a template.
Returns:	(tid, template_or_record)
Return type:	tuple

template_lines()¶

Iterator that yields the string defining a template in a .jsv file. For example:

>>> coll = jsv.JSVCollection()
>>> coll['template_1'] = '{"key_1"}'
>>> for s in coll.template_lines():
...     print(s)
...
#_ {}
#template_1 {"key_1"}

See get_template_line()

templates¶

>>> coll = jsv.JSVCollection()
    >>> coll['template_1'] = '{"key_1"}'
    >>> coll['template_2'] = '{"key_2"}'
    >>> coll.templates['{"key_1"}']
    'template_1'

Also allows testing for containment with the in operator:

>>> '{"key_1"}' in coll.templates
True
>>> '{"key_5"}' in coll.templates
False

Type:	Object that allows reverse lookup of template id from a given template. For example

class jsv.JSVTemplate(key_source='{}')¶

Class for decoding and encoding json records in jsv format.

A Template object stores the key structure for a json-compatible python object. It can then serialize or deserialize any object that conforms to that key structure in a string which is similar in structure to json, but in which the keys are omitted.

Parameters:	key_source (str or json-compatible object) – if a string, this must be a valid template string; if not, a `JSVTemplateDecodeError` will be raised. If a json-compatible object, the key structure will be extracted, with keys in alphabetical order.

decode(s)¶

Decode a jsv string into a json-compatible object

Parameters:	s (str) – s represents a json object that has been encoded with the given template. If it does not conform to the template, or is not parsable as jsv, a `JSVRecordDecodeError` will be raised.

encode(obj)¶

Encode a json-compatible object into jsv

Parameters:	obj (json-compatible object) – obj must also conform to the key structure of the Template, otherwise an error will be raised.

Exceptions¶

class jsv.JSVTemplateDecodeError(msg, pos)¶: An error occurred while decoding a str or object into a JSVTemplate.

class jsv.JSVRecordDecodeError(msg, pos)¶: An error occurred while decoding a str representing a record into an object.