This section gives a brief overview on how to use Sickle for querying OAI interfaces.

Initialize an OAI Interface

To make a connection to an OAI interface, you need to import the Sickle object:

>>> from sickle import Sickle

Next, you can initialize the connection by passing it the basic URL. In our example, we use the OAI interface of the ELIS repository:

>>> sickle = Sickle('http://elis.da.ulcc.ac.uk/cgi/oai2')

Issuing Requests

Sickle provides methods for each of the six OAI verbs (ListRecords, GetRecord, Idenitfy, ListSets, ListMetadataFormats, ListIdentifiers). Start with a ListRecords request:

>>> records = sickle.ListRecords(metadataPrefix='oai_dc')

Note that all keyword arguments you provide to this function are passed to the OAI interface as HTTP parameters. Therefore the example request would send the parameters verb=ListRecords&metadataPrefix=oai_dc. We can add additional parameters, like, for example, an OAI set:

>>> records = sickle.ListRecords(metadataPrefix='oai_dc', set='driver')

Consecutive Harvesting

Since most OAI verbs yield more than one element, their respective Sickle methods return iterator objects which can be used to iterate over the records of a repository:

>>> records = sickle.ListRecords(metadataPrefix='oai_dc')
>>> records.next()
<Record oai:eprints.rclis.org:4088>

Note that this works with all verbs that return more than one element. These are: ListRecords(), ListIdentifiers(), ListSets(), and ListMetadataFormats().

The following example shows how to iterate over the headers returned by ListIdentifiers:

>>> headers = sickle.ListIdentifiers(metadataPrefix='oai_dc')
>>> headers.next()
<Header oai:eprints.rclis.org:4088>

Iterating over the the sets returned by ListSets works similarly:

>>> sets = sickle.ListSets()
>>> sets.next()
<Set Status = In Press>

Using the from Parameter

If you need to perform selective harvesting by date using the from parameter, you may face the problem that from is a reserved word in Python:

>>> records = sickle.ListRecords(metadataPrefix='oai_dc', from="2012-12-12")
  File "<stdin>", line 1
    records = sickle.ListRecords(metadataPrefix='oai_dc', from="2012-12-12")
SyntaxError: invalid syntax

Fortunately, you can circumvent this problem by using a dictionary together with the ** operator:

>>> records = sickle.ListRecords(
...             **{'metadataPrefix': 'oai_dc',
...             'from': '2012-12-12'
...            })

Getting a Single Record

OAI-PMH allows you to get a single record by using the GetRecord verb:

>>> sickle.GetRecord(identifier='oai:eprints.rclis.org:4088',
...                  metadataPrefix='oai_dc')
<Record oai:eprints.rclis.org:4088>

Harvesting OAI Items vs. OAI Responses

Sickle supports two harvesting modes that differ in the type of the returned objects. The default mode returns OAI-specific items (records, headers etc.) encoded as Python objects as seen earlier. If you want to save the whole XML response returned by the server, you have to pass the sickle.iterator.OAIResponseIterator during the instantiation of the Sickle object:

>>> sickle = Sickle('http://elis.da.ulcc.ac.uk/cgi/oai2', iterator=OAIResponseIterator)
>>> responses = Sickle.ListRecords(metadataPrefix='oai_dc')
>>> responses.next()
<OAIResponse ListRecords>

You could then save the returned responses to disk:

>>> with open('response.xml', 'w') as fp:
...     fp.write(responses.next().raw.encode('utf8'))

Ignoring Deleted Records

The ListRecords() and ListIdentifiers() methods accept an optional parameter ignore_deleted. If set to True, the returned OAIItemIterator will skip deleted records/headers:

>>> records = sickle.ListRecords(metadataPrefix='oai_dc', ignore_deleted=True)


This works only using the sickle.iterator.OAIItemIterator. If you use the sickle.iterator.OAIResponseIterator, the resulting OAI responses will still contain the deleted records.