Reading and Writing JSON Data

For performance and replicability reasons it is generally better to keep a local copy of the data-set that is being worked on. Polymatheia supports this in two ways, either using JSON or using XML.

Writing JSON data

To store data locally, use the JSONWriter, providing the name of the directory to store the data in and the dotted path to the field that contains each record’s unique identifier:

from import EuropeanaSearchReader
from import JSONWriter

EUROPEANA_API_KEY = 'Put your key here'
reader = EuropeanaSearchReader(EUROPEANA_API_KEY, 'Gutzkow OR Zäunemann OR Heyse')
writer = JSONWriter('europeana_json', 'guid')

The filename is calculated as a sha-256 digest of the value of the unique identifier. Thus if the identifier is not actually unique, data will be overwritten and lost.

Reading JSON data

To load data stored locally, use the JSONReader, providing the name of the directory that contains the data to load:

from import JSONReader

reader = JSONReader('europeana_json')
for record in reader:

This will work with any data stored as JSON, not just with data stored using the JSONWriter. The only requirements are that the files to load must have “.json” as their extension and each file must contain exactly one record.


The order of records is defined by order in which filenames are listed by the underlying operating system. As such no order can be guaranteed.