Week 2 — Database Entries
The DatabaseEntry class
In the last blog post, I have used the class DatabaseEntry without really explaining it. That may have confused the reader but I had a reason for doing so: the public API was not final at all. The class didn't have any methods and the attributes were not decided yet. The class DatabaseEntry represents the main table of the database and each instance of this class represents one database entry. Each attribute is one field in the database table.
adding information from a FITS file
I added a new method add_fits_header_entries_from_file. With it, the information from a FITS file can easily be added to a database entry. FITS files usually contain a lot of metadata about the observation like the time it took place, which instrument has been used etc. The passed argument may be a path to a FITS file or any file-like object (e.g. an instance of StringIO.StringIO). The saved information is saved in the attribute fits_header_entries which is a list of FitsHeaderEntry instances. The class FitsHeaderEntry holds the attributes id, key, and value. Here is an example:
>>> from pprint import pprint
>>> import sunpy
>>> from sunpy.database import DatabaseEntry
>>> entry = DatabaseEntry()
>>> entry.add_fits_header_entries_from_file(sunpy.RHESSI_EVENT_LIST)
>>> pprint(entry.fits_header_entries)
[<FitsHeaderEntry(id None, key 'SIMPLE', value True)>,
<FitsHeaderEntry(id None, key 'BITPIX', value 8)>,
<FitsHeaderEntry(id None, key 'NAXIS', value 0)>,
<FitsHeaderEntry(id None, key 'EXTEND', value True)>,
<FitsHeaderEntry(id None, key 'DATE', value '2011-09-13T15:37:38')>,
<FitsHeaderEntry(id None, key 'ORIGIN', value 'RHESSI')>,
<FitsHeaderEntry(id None, key 'OBSERVER', value 'Unknown')>,
<FitsHeaderEntry(id None, key 'TELESCOP', value 'RHESSI')>,
<FitsHeaderEntry(id None, key 'INSTRUME', value 'RHESSI')>,
<FitsHeaderEntry(id None, key 'OBJECT', value 'Sun')>,
<FitsHeaderEntry(id None, key 'DATE_OBS', value '2002-02-20T11:06:00.000')>,
<FitsHeaderEntry(id None, key 'DATE_END', value '2002-02-20T11:06:43.330')>,
<FitsHeaderEntry(id None, key 'TIME_UNI', value 1)>,
<FitsHeaderEntry(id None, key 'ENERGY_L', value 25.0)>,
<FitsHeaderEntry(id None, key 'ENERGY_H', value 40.0)>,
<FitsHeaderEntry(id None, key 'TIMESYS', value '1979-01-01T00:00:00')>,
<FitsHeaderEntry(id None, key 'TIMEUNIT', value 'd')>]
generating entries by a VSO query response
With the sunpy.net.vso package, solar data can be queried and downloaded. If a query is issued, a query response is returned. This query response can be used to create an iterator of database entries. They are not yet saved in a database though. To save them, a database connection has to be established and the entries have to be added explicitly. See the last post about the Database class for more information. Also see the documentation of the VSO package for more information about its usage.
>>> from sunpy.net.vso import VSOClient
>>> from sunpy.database import entries_from_query_result
>>> client = VSOClient()
>>> qr = client.query_legacy('2001/1/1', '2001/1/2', instrument='EIT')
>>> entries = entries_from_query_result(qr)
>>> entries.next()
<DatabaseEntry(id None, data provider SDAC, fileid /archive/soho/private/data/processed/eit/lz/2001/01/efz20010101.010014)>