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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<TITLE>Queue - A Queue Implementation for Python</TITLE>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<STYLE TYPE="text/css">
p { text-align: justify; }
ul.indent { }
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</STYLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000EE" VLINK="#551A8B" ALINK="#FF0000">
<HR NOSHADE WIDTH="100%">
<H2>mxQueue - A Queue Implementation for Python</H2>
<HR SIZE=1 NOSHADE WIDTH="100%">
<TABLE WIDTH="100%">
<TR>
<TD>
<SMALL>
<A HREF="#Interface">Interface</A> :
<A HREF="#Examples">Examples</A> :
<A HREF="#API">C API</A> :
<A HREF="#Structure">Structure</A> :
<A HREF="#Support">Support</A> :
<A HREF="http://www.egenix.com/files/python/eGenix-mx-Extensions.html#Download-mxBASE"><B>Download</B></A> :
<A HREF="#Copyright">Copyright & License</A> :
<A HREF="#History">History</A> :
<A HREF="" TARGET="_top">Home</A>
</SMALL>
</TD>
<TD ALIGN=RIGHT VALIGN=TOP>
<SMALL>
<FONT COLOR="#FF0000">Version 2.0.3</FONT>
</SMALL>
</TD>
</TABLE>
<HR SIZE=1 NOSHADE WIDTH="100%">
<H3>Introduction</H3>
<UL CLASS="indent">
<HR>
<P>
<B>XXX This documentation is unfinished...</B> it is
basically a search&replace copy of the mxStack documentation
since the mxQueue APIs are very similar to mxStack. Usage
should be straight forward though. The next release will
have proper documentation and also be advertised on the
download page :-).
<HR>
<P>
Though queues can be emulated with Python lists, this type
provides a simple interface to the data structure, both in
Python and in C. Because of the function call overhead
calling the methods from Python it is only a tad faster than
a corresponding list emulation. Called from within an C
extension shows a more significant performance increase. The
included <TT>queuebench.py</TT> gives an impression of how
the different methods relate w/r to speed:
<PRE>
projects/Queue> python1.5 -O queuebench.py 1000 100 100
list: 1.11
tuples: 0.6
Queue (with push + pop): 0.72
Queue (with push + pop_many): 0.5
Queue (with << + >>): 0.85
Queue (with push_many + pop_many): 0.47
UserQueue: 1.79
</PRE>
<P>
Note that the tuple version has a few disadvantages when
used for big queues: for one it uses lots of memory (20
bytes per entry slot; Queue uses 20 bytes + 4 bytes per
entry slot) and deallocation can become a problem -- this is
done using recursion with one level per queue element. For
small queues it still is unbeatable, though (it has no
function call overhead). BTW, the UserQueue implementation
uses the same technique: the figures shown mainly result
from Python method call overhead.
<P>
Because queues are normally used only temporarily, the Queue
implementation only grows the memory buffer used for holding
the entry slots. It never shrinks it. This has an advantage
of reducing malloc overhead when doing e.g. depth first
search, but also the disadvantage of using more memory in
degenerate cases. To compensate for this, simply call the
.resize() method every now and then. It forces the used
buffer to be resized.
<P>
</UL><!--CLASS="indent"-->
<A NAME="Interface">
<H3>Interface</H3>
<UL CLASS="indent">
<P><B>Queue Constructors</B>
<P>There are two ways to construct a <TT>Queue</TT> from scratch:
<P><DL>
<DT><CODE><FONT COLOR="#000099">
Queue([initial_size])
</FONT></CODE></DT>
<DD>Returns a new empty Queue instance allocating at least
the given number of slots for queue elements. If the
parameter is not given a reasonable default is
chosen.</DD><P>
<DT><CODE><FONT COLOR="#000099">
QueueFromSequence(seq)
</FONT></CODE></DT>
<DD>Constructs a Queue instance from the given sequence. The
instance is filled with all the elements found in the
sequence by pushing the items from index 0 to len(seq)-1 in
that order, i.e. popping all elements from the Queue results
in a reversed sequence. </DD><P>
</DL>
<B>Instance Methods</B>
<P>A <TT>Queue</TT> instance has the following methods:
<P><DL>
<DT><CODE><FONT COLOR="#000099">
push(x)</FONT></CODE></DT>
<DD>
Pushes the object x onto the queue.</DD><P>
<DT><CODE><FONT COLOR="#000099">
push_many(sequences)</FONT></CODE></DT>
<DD>
Pushes the objects in <CODE>sequence</CODE> from left to
right onto the queue. If errors occur during this process,
the already pushed elements are discarded from the queue
and it returns to its original state.</CODE></DD><P>
<DT><CODE><FONT COLOR="#000099">
pop()</FONT></CODE></DT>
<DD>
Pops the top element off of the queue.</DD><P>
<DT><CODE><FONT COLOR="#000099">
pop_many(n)</FONT></CODE></DT>
<DD>
Pops the top <CODE>n</CODE> elements and returns them in
form of a tuple. If less than <CODE>n</CODE> elements are
on the queue, the tuple will contain all queue entries and
the queue will then be empty again. The order is top to
bottom, i.e. <CODE>s.pop_many(2) ==
(s.pop(),s.pop())</CODE></DD><P>
<DT><CODE><FONT COLOR="#000099">
as_tuple()</FONT></CODE></DT>
<DD>
Returns the queue's content as tuple, without modifying
it.</DD><P>
<DT><CODE><FONT COLOR="#000099">
as_list()</FONT></CODE></DT>
<DD>
Returns the queue's content as list, without modifying
it.</DD><P>
<DT><CODE><FONT COLOR="#000099">
clear()</FONT></CODE></DT>
<DD>
Clears the queue.</DD><P>
<DT><CODE><FONT COLOR="#000099">
resize([size=len(queue)])</FONT></CODE></DT>
<DD>
Resize the queue buffer to hold at least <CODE>size</CODE>
entries.
<P>
You can call this method without argument to force the
queue to shrink its memory buffer to the minimal limit
needed to hold the contained elements. </DD><P>
</DL>
<P>Note that no method for testing emtpyness is provided. Use
len() for that or simply test for trueness, e.g. <CODE>while
s: print s.pop()</CODE> will loop as long as there are
elements left on the Queue s. This is much faster than going
through the method calling process -- even when the method
being called is written in C.
<P>
</UL><!--CLASS="indent"-->
<A NAME="Examples">
<H3>Examples of Use</H3>
<UL CLASS="indent">
<P>Well, there's not much to show:
<FONT COLOR="#000099"><PRE>
from mx.Queue import *
s = Queue()
for i in range(1000):
s.push(i)
while s:
print s.pop()
# which could also be done as:
s = QueueFromSequence(range(1000))
while s:
print s.pop()
# or a little different
s = QueueFromSequence(range(1000))
print s.as_tuple()
print s.as_list()
</PRE></FONT>
</UL><!--CLASS="indent"-->
<A NAME="API">
<H3>Supported Data Types in the C-API</H3>
<UL CLASS="indent">
<P>Please have look at the file <TT>mxQueue.h</TT> for
details. Basically all of the above Python interfaces are
also available in the C API.
<P>To access the module, do the following (note the
similarities with Python's way of accessing functions from a
module):
<PRE>
#include "mxQueue.h"
...
PyObject *v;
/* Import the mxQueue module */
if (mxQueue_ImportModuleAndAPI())
goto onError;
/* Access functions from the exported C API through mxQueue */
v = mxQueue.Queue(0);
if (!v)
goto onError;
/* Type checking */
if (mxQueue_Check(v))
printf("Works.\n");
Py_DECREF(v);
...
</PRE>
<P>
</UL><!--CLASS="indent"-->
<A NAME="Structure">
<H3>Package Structure</H3>
<UL CLASS="indent">
<PRE>
[Queue]
mxQueue
</PRE>
<P>Entries enclosed in brackets are packages (i.e. they are
directories that include a <TT>__init__.py</TT> file). Ones
without brackets are just simple subdirectories that are not
accessible via <CODE>import</CODE>. These are used for
compiling the C extension modules which will get installed in
the same place where all your other site specific extensions
live (e.g. <TT>/usr/local/lib/python-x.xx/site-packages</TT>).
<P>The package Queue imports all symbols from the extension
mxQueue, so <CODE>import Queue; s = Queue.Queue()</CODE> gives
you a Queue instance in <CODE>s</CODE>.
<P>
</UL><!--CLASS="indent"-->
<A NAME="Support">
<H3>Support</H3>
<UL CLASS="indent">
<P>
eGenix.com is providing commercial support for this
package. If you are interested in receiving information
about this service please see the <A
HREF="http://www.egenix.com/files/python/eGenix-mx-Extensions.html#Support">eGenix.com
Support Conditions</A>.
</UL><!--CLASS="indent"-->
<A NAME="Copyright">
<H3>Copyright & License</H3>
<UL CLASS="indent">
<P>
© 1999-2000, Copyright by Marc-André Lemburg;
All Rights Reserved. mailto: <A
HREF="mailto:mal@lemburg.com">mal@lemburg.com</A>
<P>
© 2000-2001, Copyright by eGenix.com Software GmbH,
Langenfeld, Germany; All Rights Reserved. mailto: <A
HREF="mailto:info@egenix.com">info@egenix.com</A>
<P>
This software is covered by the <A
HREF="mxLicense.html#Public"><B>eGenix.com Public
License Agreement</B></A>. The text of the license is also
included as file "LICENSE" in the package's main directory.
<P>
<B> By downloading, copying, installing or otherwise using
the software, you agree to be bound by the terms and
conditions of the eGenix.com Public License
Agreement. </B>
</UL><!--CLASS="indent"-->
<A NAME="History">
<H3>History & Future</H3>
<UL CLASS="indent">
<P>There were no significant changes between 2.0.2 and 2.0.3.
<P>Changes from version 2.0.0 to 2.0.2:
<UL>
<LI> Fixed a bug in the coercion code which surfaced due to
the rich comparison changes in Python 2.1. Python 2.1 will
now compare Queue objects to other objects without raising a
TypeError.
</UL>
<P>Version 2.0.0 was the initial public version.
</UL><!--CLASS="indent"-->
<HR WIDTH="100%">
<CENTER><FONT SIZE=-1>
<P>
© 1999-2000, Copyright by Marc-André Lemburg;
All Rights Reserved. mailto: <A
HREF="mailto:mal@lemburg.com">mal@lemburg.com</A>
<P>
© 2000-2001, Copyright by eGenix.com Software GmbH;
All Rights Reserved. mailto: <A
HREF="mailto:info@egenix.com">info@egenix.com</A>
</FONT></CENTER>
</FONT></CENTER>
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