The Python bindings for Xapian are packaged in the
and largely follow the C++ API, with the following differences and
additions. Python strings and lists, etc., are converted automatically
in the bindings, so generally it should just work as expected.
examples subdirectory contains examples showing how to use the
Python bindings based on the simple examples from
which shows how to define a MatchDecider in Python.
The Python bindings come with a test suite, consisting of two test files:
pythontest.py. These are run by the
make check" command, or may be run manually. By default, they
will display the names of any tests which failed, and then display a count of
tests which run and which failed. The verbosity may be increased by setting
VERBOSE" environment variable: a value of 1 will display
detailed information about failures, and a value of 2 will display further
information about the progress of tests.
Xapian exceptions are translated into Python exceptions with the same names
and inheritance hierarchy as the C++ exception classes. The base class of
all Xapian exceptions is the
xapian.Error class, and this in
turn is a child of the standard python
This means that programs can trap all xapian exceptions using "
xapian.Error", and can trap all exceptions which don't indicate that
the program should terminate using "
The xapian Python bindings accept unicode strings as well as simple strings (ie, "str" type strings) at all places in the API which accept string data. Any unicode strings supplied will automatically be translated into UTF-8 simple strings before being passed to the Xapian core. The Xapian core is largely agnostic about character encoding, but in those places where it does process data in a character encoding dependent way it assumes that the data is in UTF-8. The Xapian Python bindings always return string data as simple strings.
Therefore, in order to avoid issues with character encodings, you should
always pass text data to Xapian as unicode strings, or UTF-8 encoded simple
strings. There is, however, no requirement for simple strings passed into
Xapian to be valid UTF-8 encoded strings, unless they are being passed to a
text processing routine (such as the query parser, or the stemming
algorithms). For example, it is perfectly valid to pass arbitrary binary
data in a simple string to the
It is often useful to normalise unicode data before passing it to Xapian -
Xapian currently has no built-in support for normalising unicode
representations of data. The standard python module
unicodedata" provides support for normalising unicode: you
probably want the "
NFKC" normalisation scheme: in other words,
use something like
to normalise the string "foo" before passing it to Xapian.
The iterator classes in the Xapian C++ API are wrapped in a "Pythonic" style.
The following are supported (where marked as default iterator, it means
__iter__() does the right
thing so you can for instance use
for term in document to
iterate over terms in a Document object):
|Class||Method||Equivalent to||Iterator type|
The pythonic iterators generally return Python objects, with properties
available as attribute values, with lazy evaluation where appropriate. An
exception is the
PositionIter object returned by
Database.positionlist, which returns an integer.
The lazy evaluation is mainly transparent, but does become visible in one situation: if you keep an object returned by an iterator, without evaluating its properties to force the lazy evaluation to happen, and then move the iterator forward, the object may no longer be able to efficiently perform the lazy evaluation. In this situation, an exception will be raised indicating that the information requested wasn't available. This will only happen for a few of the properties - most are either not evaluated lazily (because the underlying Xapian implementation doesn't evaluate them lazily, so there's no advantage in lazy evaluation), or can be accessed even after the iterator has moved. The simplest work around is simply to evaluate any properties you wish to use which are affected by this before moving the iterator. The complete set of iterator properties affected by this is:
In older releases, the pythonic iterators returned lists representing the
appropriate item when their
next() method was called. These were
removed in Xapian 1.1.0.
Before the pythonic iterator wrappers were added, the python bindings provided thin wrappers around the C++ iterators. However, these iterators don't behave like most iterators do in Python, so the pythonic iterators were implemented to replace them. The non-pythonic iterators are still available to allow existing code to continue to work, but they're now deprecated and we plan to remove them in Xapian 1.3.0. The documentation below is provided to aid migration away from them.
All non-pythonic iterators support
to move through and test iterators (as for all language bindings).
MSetIterator and ESetIterator also support
Python-wrapped iterators also support direct comparison, so something like:
m=mset.begin() while m!=mset.end(): # do something m.next()
C++ iterators are often dereferenced to get information, eg
(*it). With Python these are all mapped to named methods, as
Other methods, such as
MSet objects have some additional methods to simplify access (these work using the C++ array dereferencing):
|returns MSetItem at index|
Additionally, the MSet has a property,
mset.items, which returns a
list of tuples representing the MSet; this may be more convenient than using
an MSetIter. The members of the tuple are as follows.
Two MSet objects are equal if they have the same number and maximum possible number of members, and if every document member of the first MSet exists at the same index in the second MSet, with the same weight.
The ESet has a property,
eset.items, which returns a list of
tuples representing the ESet; this may be more convenient than using the
ESetIterator. The members of the tuple are as follows.
The C++ API contains a few non-class functions (the Database factory functions, and some functions reporting version information), which are wrapped like so for Python:
Xapian::version_string()is wrapped as
Xapian::major_version()is wrapped as
Xapian::minor_version()is wrapped as
Xapian::revision()is wrapped as
Xapian::Auto::open_stub()is wrapped as
Xapian::Brass::open()is wrapped as
Xapian::Chert::open()is wrapped as
Xapian::Flint::open()is wrapped as
Xapian::InMemory::open()is wrapped as
Xapian::Remote::open()is wrapped as
xapian.remote_open()(both the TCP and "program" versions are wrapped - the SWIG wrapper checks the parameter list to decide which to call).
Xapian::Remote::open_writable()is wrapped as
xapian.remote_open_writable()(both the TCP and "program" versions are wrapped - the SWIG wrapper checks the parameter list to decide which to call).
In C++ there's a Xapian::Query constructor which takes a query operator and start/end iterators specifying a number of terms or queries, plus an optional parameter. In Python, this is wrapped to accept any Python sequence (for example a list or tuple) to give the terms/queries, and you can specify a mixture of terms and queries if you wish. For example:
subq = xapian.Query(xapian.Query.OP_AND, "hello", "world") q = xapian.Query(xapian.Query.OP_AND, [subq, "foo", xapian.Query("bar", 2)])
As of 1.1.1, these are wrapped as
There is an additional method
get_matching_terms() which takes
an MSetIterator and returns a list of terms in the current query which
match the document given by that iterator. You may find this
more convenient than using the TermIterator directly.
Custom MatchDeciders can be created in Python; simply subclass xapian.MatchDecider, ensure you call the super-constructor, and define a __call__ method that will do the work. The simplest example (which does nothing useful) would be as follows:
class mymatchdecider(xapian.MatchDecider): def __init__(self): xapian.MatchDecider.__init__(self) def __call__(self, doc): return 1
The ValueRangeProcessor class (and its subclasses) provide an operator() method (which is exposed in python as a __call__() method, making the class instances into callables). This method checks whether a beginning and end of a range are in a format understood by the ValueRangeProcessor, and if so, converts the beginning and end into strings which sort appropriately. ValueRangeProcessors can be defined in python (and then passed to the QueryParser), or there are several default built-in ones which can be used.
Unfortunately, in C++ the operator() method takes two std::string arguments by reference, and returns values by modifying these arguments. This is not possible in Python, since strings are immutable objects. Instead, in the Python implementation, when the __call__ method is called, the resulting values of these arguments are returned as part of a tuple. The operator() method in C++ returns a value number; the return value of __call__ in python consists of a 3-tuple starting with this value number, followed by the returned "begin" value, followed by the returned "end" value. For example:
vrp = xapian.NumberValueRangeProcessor(0, '$', True) a = '$10' b = '20' slot, a, b = vrp(a, b)
Additionally, a ValueRangeProcessor may be implemented in Python. The Python implementation should override the __call__() method with its own implementation, and, again, since it cannot return values by reference, it should return a tuple of (value number, begin, end). For example:
class MyVRP(xapian.ValueRangeProcessor): def __init__(self): xapian.ValueRangeProcessor.__init__(self) def __call__(self, begin, end): return (7, "A"+begin, "B"+end)
By default, both mod_python and mod_wsgi use a separate sub-interpreter for each application. However, Python's sub-interpreter support is incompatible with the simplified GIL state API which SWIG-generated Python bindings use by default. So to avoid deadlocks, you need to tell mod_python and mod_wsgi to run applications which use Xapian in the main interpreter as detailed below.
This restriction could be removed - the details are in Xapian's bugtracker - see ticket #364 for details of what needs doing.
You need to set this option in the Apache configuration section for all mod_python scripts which use Xapian:
You may also need to use Python >= 2.4 (due to problems in Python 2.3 with the APIs the code uses).
You need to set the WSGIApplicationGroup option like so:
The mod_wsgi documentation also discusses this issue.Last updated $Date: 2010-02-03 15:12:00 +0000 (Wed, 03 Feb 2010) $