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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<TITLE>Stack - A Stack 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 { }
body { }
</STYLE>
</HEAD>
<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000EE" VLINK="#551A8B" ALINK="#FF0000">
<HR NOSHADE WIDTH="100%">
<H2>mxStack - A Stack Implementation for Python</H2>
<HR SIZE=1 NOSHADE WIDTH="100%">
<TABLE WIDTH="100%">
<TR>
<TD>
<SMALL>
<A HREF="#Interface">Interface</A> :
<A HREF="#Constants">Constants</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 2.1.0</FONT>
</SMALL>
</TD>
</TABLE>
<HR SIZE=1 NOSHADE WIDTH="100%">
<H3>Introduction</H3>
<UL CLASS="indent">
<P>
Though stacks 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>stackbench.py</TT> gives an impression of how
the different methods relate w/r to speed:
<PRE>
mx/Stack> python stackbench.py 1000 100 10
list: 0.24
tuples: 0.15
Stack (with push + pop): 0.17
Stack (with push + pop_many): 0.17
Stack (with << + >>): 0.19
Stack (with push_many + pop_many): 0.17
UserStack: 0.33
</PRE>
<P>
Note that the tuple version has a few disadvantages when
used for big stacks: for one it uses lots of memory (20
bytes per entry slot; Stack uses 20 bytes + 4 bytes per
entry slot) and deallocation can become a problem -- this is
done using recursion with one level per stack element. For
small stacks it still is unbeatable, though (it has no
function call overhead). BTW, the UserStack implementation
uses the same technique: the figures shown mainly result
from Python method call overhead.
<P>
Because stacks are normally used only temporarily, the Stack
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>
The mxStack package defines the following interfaces.
<H4>Stack Constructors</H4>
<UL CLASS="indent">
<P>There are two ways to construct a <TT>Stack</TT> from scratch:
<P><DL>
<DT><CODE><FONT COLOR="#000099">
Stack([initial_size])
</FONT></CODE></DT>
<DD>Returns a new empty Stack instance allocating at least
the given number of slots for stack elements. If the
parameter is not given a reasonable default is
chosen.</DD><P>
<DT><CODE><FONT COLOR="#000099">
StackFromSequence(seq)
</FONT></CODE></DT>
<DD>Constructs a Stack 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 Stack results
in a reversed sequence. </DD><P>
</DL>
</UL><!--CLASS="indent"-->
<H4>Stack Instance Methods</H4>
<UL CLASS="indent">
<P>A <TT>Stack</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 stack.</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 stack. If errors occur during this process,
the already pushed elements are discarded from the stack
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 stack.</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 stack, the tuple will contain all stack entries and
the stack 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 stack's content as tuple, without modifying
it.</DD><P>
<DT><CODE><FONT COLOR="#000099">
as_list()</FONT></CODE></DT>
<DD>
Returns the stack's content as list, without modifying
it.</DD><P>
<DT><CODE><FONT COLOR="#000099">
clear()</FONT></CODE></DT>
<DD>
Clears the stack.</DD><P>
<DT><CODE><FONT COLOR="#000099">
resize([size=len(stack)])</FONT></CODE></DT>
<DD>
Resize the stack buffer to hold at least <CODE>size</CODE>
entries.
<P>
You can call this method without argument to force the
stack to shrink its memory buffer to the minimal limit
needed to hold the contained elements. </DD><P>
<DT><CODE><FONT COLOR="#000099">
__getitem__(index)</FONT></CODE></DT>
<DD>
This is not really a method, but a slot providing access
to the items on the Stack without popping them off the
Stack.
<P>
<CODE>index</CODE> works just like for Python lists,
i.e. negative indices are normalized using the current
length of the Stack.
<P>
An <CODE>IndexError</CODE> is raised for invalid
indices. This makes the Stack compatible to the
<CODE>for</CODE>-loop statement allowing you to iterate
over the Stack contents from bottom to top.
</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 Stack 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="Constants">
<H4>Constants</H4>
<UL CLASS="indent">
<P>
<DL>
<DT><CODE><FONT COLOR="#000099">
Error</FONT></CODE></DT>
<DD>
Error class used for package specific errors. It is a
subclass of exceptions.IndexError.</DD><P>
<DT><CODE><FONT COLOR="#000099">
EmptyError</FONT></CODE></DT>
<DD>
Error class used to signal an empty queue. It is a
subclass of Error.</DD><P>
</DL>
<P>
</UL><!--CLASS="indent"-->
</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.Stack import *
s = Stack()
for i in range(1000):
s.push(i)
while s:
print s.pop()
# which could also be done as:
s = StackFromSequence(range(1000))
while s:
print s.pop()
# or a little different
s = StackFromSequence(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>mxStack.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 "mxStack.h"
...
PyObject *v;
/* Import the mxStack module */
if (mxStack_ImportModuleAndAPI())
goto onError;
/* Access functions from the exported C API through mxStack */
v = mxStack.Stack(0);
if (!v)
goto onError;
/* Type checking */
if (mxStack_Check(v))
printf("Works.\n");
Py_DECREF(v);
...
</PRE>
<P>
</UL><!--CLASS="indent"-->
<A NAME="Structure">
<H3>Package Structure</H3>
<UL CLASS="indent">
<PRE>
[Stack]
mxStack
</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 Stack imports all symbols from the extension
mxStack, so <CODE>import Stack; s = Stack.Stack()</CODE> gives
you a Stack 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>
© 1998-2000, Copyright by Marc-André Lemburg;
All Rights Reserved. mailto: <A
HREF="mailto:mal@lemburg.com">mal@lemburg.com</A>
<P>
© 2000-2004, 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>Changes from version 2.0.3 to 2.1.0:
<UL>
<LI> Documented the exception objects used by the package.
Added EmptyError exception.
</UL>
<P>There were no significant changes between 2.0.2 and 2.0.3.
<P>Changes from 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 Stack objects to other objects
without raising a TypeError.
</UL>
<P>Changes from <A HREF="mxStack-0.2.zip">0.2.2</A> to 2.0.0:
<UL>
<LI>Added .pop_many(), .resize() and .clear().
<P><LI>Added mxStack_PopMany, mxStack_PushMany,
mxStack_Clear, mxStack_Length to the C API.
<P><LI>Fixed a memory leak in StackFromSequence().
<P><LI>Fixed in bug in the non-zero testing code.
<P><LI>Added __getitem__ slot and mxStack_GetItem C API.
After an idea by Adam Deprince.
<P><LI> <B>Moved</B> the package under a new top-level
package 'mx'. It is part of the <I>eGenix.com mx BASE
distribution</I>.
</UL>
<P>Changes from <A HREF="mxStack-0.1.zip">0.1</A> to 0.2.2:
<UL>
<LI>Version 0.2.2: Fixed a bug that caused stack.push()
to dump core when called without argument. Also added some
minor speedups.
<P><LI>Version 0.2.1: added method pop_many().
<P><LI>Converted the module into a package called
'Stack'. This imports the C extension mxStack.
</UL>
<P>
</UL><!--CLASS="indent"-->
<HR WIDTH="100%">
<CENTER><FONT SIZE=-1>
<P>
© 1998-2000, Copyright by Marc-André Lemburg;
All Rights Reserved. mailto: <A
HREF="mailto:mal@lemburg.com">mal@lemburg.com</A>
<P>
© 2000-2004, 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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