# Indexing and parsing dates/times

## Indexing dates

Whoosh lets you index and search dates/times using the :class:whoosh.fields.DATETIME field type. Instead of passing text for the field in add_document(), you use a Python datetime.datetime object:

from datetime import datetime, timedelta
from whoosh import fields, index

schema = fields.Schema(title=fields.TEXT, content=fields.TEXT,
date=fields.DATETIME)
ix = index.create_in("indexdir", schema)

w = ix.writer()
w.add_document(title="Document 1", content="Rendering images from the command line",
date=datetime.utcnow())
date=datetime.utcnow() + timedelta(days=1))
w.commit()


## Parsing date queries

Once you've have an indexed DATETIME field, you can search it using a rich date parser contained in the :class:whoosh.qparser.dateparse.DateParserPlugin:

from whoosh import index
from whoosh.qparser import QueryParser
from whoosh.qparser.dateparse import DateParserPlugin

ix = index.open_dir("indexdir")

# Instatiate a query parser
qp = QueryParser("content", ix.schema)

# Add the DateParserPlugin to the parser


With the DateParserPlugin, users can use date queries such as:

20050912
2005 sept 12th
june 23 1978
23 mar 2005
july 1985
sep 12
today
yesterday
tomorrow
now
next friday
last tuesday
5am
10:25:54
23:12
8 PM
4:46 am oct 31 2010
last tuesday to today
today to next friday
jan 2005 to feb 2008
-1 week to now
now to +2h
-1y6mo to +2 yrs 23d


Normally, as with other types of queries containing spaces, the users needs to quote date queries containing spaces using single quotes:

render date:'last tuesday' command
date:['last tuesday' to 'next friday']


If you use the free argument to the DateParserPlugin, the plugin will try to parse dates from unquoted text following a date field prefix

This allows the user to type a date query with spaces and special characters following the name of date filed and a colon. The date query can be mixed with other types of queries without quotes:

date:last tuesday
render date:oct 15th 2001 5:20am command


If you don't use the DateParserPlugin, users can still search DATETIME fields using a simple numeric form YYYY[MM[DD[hh[mm[ss]]]]] that is built into the DATETIME field:

from whoosh import index
from whoosh.qparser import QueryParser

ix = index.open_dir("indexdir")
qp = QueryParser("content", schema=ix.schema)

# Find all datetimes in 2005
q = qp.parse(u"date:2005")

# Find all datetimes on June 24, 2005
q = qp.parse(u"date:20050624")

# Find all datetimes from 1am-2am on June 24, 2005
q = qp.parse(u"date:2005062401")

# Find all datetimes from Jan 1, 2005 to June 2, 2010
q = qp.parse(u"date:[20050101 to 20100602]")


## About time zones and basetime

The best way to deal with time zones is to always index datetimes in naive UTC form. Any tzinfo attribute on the datetime object is _ignored_ by the indexer. If you are working with local datetimes, you should convert them to naive UTC datetimes before indexing.

## Date parser notes

Please note that the date parser is still somewhat experimental.

### Setting the base datetime

When you create the DateParserPlugin you can pass a datetime object to the basedate argument to set the datetime against which relative queries (such as last tuesday and -2 hours) are measured. By default, the basedate is datetime.utcnow() at the moment the plugin is instantiated:

qp.add_plugin(DateParserPlugin(basedate=my_datetime))


### Registering an error callback

To avoid user queries causing exceptions in your application, the date parser attempts to fail silently when it can't parse a date query. However, you can register a callback function to be notified of parsing failures so you can display feedback to the user. The argument to the callback function is the date text that could not be parsed (this is an experimental feature and may change in future versions):

errors = []
errors.append(msg)

q = qp.parse(u"date:blarg")
# errors == [u"blarg"]


### Using free parsing

While the free option is easier for users, it may result in ambiguities. As one example, if you want to find documents containing reference to a march and the number 2 in documents from the year 2005, you might type:

date:2005 march 2


This query would be interpreted correctly as a date query and two term queries when free=False, but as a single date query when free=True. In this case the user could limit the scope of the date parser with single quotes:

date:'2005' march 2


### Parsable formats

The date parser supports a wide array of date and time formats, however it is not my intention to try to support all types of human-readable dates (for example ten to five the friday after next). The best idea might be to pick a date format that works and try to train users on it, and if they use one of the other formats that also works consider it a happy accident.

## Limitations

• Since it's based on Python's datetime.datetime object, the DATETIME field shares all the limitations of that class, such as no support for dates before year 1 on the proleptic Gregorian calendar. The DATETIME field supports practically unlimited dates, so if the datetime object is every improved it could support it. An alternative possibility might be to add support for mxDateTime objects someday.
• The DateParserPlugin currently only has support for English dates. The architecture supports creation of parsers for other languages, and I hope to add examples for other languages soon.
• DATETIME fields do not currently support open-ended ranges. You can simulate an open ended range by using an endpoint far in the past or future.