PythonGuido van Rossum

director of PythonLabs at Zope Corporation

mailto:guido@python.org

http://www.python.org

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What’s in a name?

• Snake logos and mascot notwithstanding, it’s named after Monty Python’s Flying Circus

• Humor-impaired can safely ignore the spam references :-)

• Nobody expects the Spanish inquisition

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What is Python?

• O-O rapid prototyping language

• Not just a scripting language

• Not just another Perl

• Easy to learn, read, use

• Extensible (add new modules)– C/C++/Fortran/whatever

– Java (through Jython)

• Embeddable in applications

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Touchy-feely properties

• Open Source (OSI Certified)– copyrighted but use not restricted

– no "viral" license

– owned by independent non-profit, PSF

• Mature (13 years old)

• Supportive user community– plenty of good books, too

• Simple design, easy to learn– reads like “pseudo-code”

– Suitable as first language

– Suitable as last language :-)

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High-level properties

• Extremely portable– Unix/Linux, Windows, Mac, PalmOS, WindowsCE,

RiscOS, VxWorks, QNX, OS/2, OS/390, AS/400, PlayStation, Sharp Zaurus, BeOS, VMS…

• Compiles to interpreted byte code– compilation is implicit and automatic

• Memory management automatic– reference counting for most situations

– GC added for cycle detection

• “Safe”: no core dumps due to your bugs

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What is it used for?

• rapid prototyping

• web programming (client and server side)

• ad hoc programming ("scripting")

• steering scientific applications

• extension language

• XML processing

• database applications

• GUI applications

• education

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Who is using it?

• Google (various projects)

• NASA (several projects)

• NYSE (one of only three languages "on the floor")

• Industrial Light & Magic (everything)

• Yahoo! (Yahoo mail & groups)

• RealNetworks (function and load testing)

• RedHat (Linux installation tools)

• LLNL, Fermilab (steering scientific applications)

• Zope Corporation (content management)

• ObjectDomain (embedded Jython in UML tool)

• Alice project at CMU (accessible 3D graphics)

• More success stories at www.pythonology.com

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Language properties

• Everything is an object

• Packages, modules, classes, functions

• Exception handling

• Dynamic typing, polymorphism

• Static scoping

• Operator overloading

• Indentation for block structure– Otherwise conventional syntax

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High-level data types

• Numbers: int, long, float, complex

• Strings, Unicode: immutable

• Lists and dictionaries: containers

• Other types for e.g. binary data, regular expressions, introspection

• Extension modules can define new“built-in” data types

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Interfaces to...

• XML– DOM, expat

– XMLRPC, SOAP, Web Services

• Relational databases– MySQL, PostgreSQL, Oracle , ODBC, Sybase, Informix

• Java (via Jython)

• Objective C

• COM, DCOM (.NET too)

• Many GUI libraries– cross-platform

• Tk, wxWindows, GTK, Qt

– platform-specific• MFC, Mac (classic, Cocoa), X11

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Compared to Perl

• Easier to learn– very important for infrequent users

• More readable code

• More maintainable code

• Fewer “magical” side effects

• More “safety” guarantees

• Better Java integration

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Compared to Java

• Code up to 5 times shorter

– and more readable

• Dynamic typing

• Multiple inheritance, operator overloading

• Quicker development

– no compilation phase

– less typing

• Yes, it may run a bit slower

– but development is much faster

– and Python uses less memory (studies show)

Similar (but more so) for C/C++

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Jython

• Seamless integration with Java

• Separate implementation

• Implements the same language

• Different set of standard modules

• differences in “gray areas”– e.g. some different introspection calls

– different command line options, etc.

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Jython's Java integration

• Interactive

• Compiles directly to Java bytecode

• Import Java classes directly

• Subclass Java classes– pass instances back to Java

• Java beans integration

• Can compile into Java class files

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Example function

def gcd(a, b):

"greatest common divisor"

while a != 0:

a, b = b%a, a # parallel assignment

return b

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Example class

class Stack:

"A well-known data structure" # doc string

def __init__(self): # constructor

self.items = []

def push(self, x):

self.items.append(x) # the sky is the limit

def pop(self):

x = self.items[-1] # what happens if it’s empty?

del self.items[-1]

return x

def empty(self):

return len(self.items) == 0

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References and plugs

• References:– www.python.org - Python home site

• documentation, downloads, community, PSF

– www.pythonology.org - success stories

– www.artima.com/intv - interview with GvR

– www.zope.org - Zope community site

– www.zope.com - Zope corporate site

• Python Conferences (see www.python.org):– PyCon DC March 26-28 Washington, DC

• on-line registration ends today ($200)

– Python UK April 2-3 Oxford, England

– EuroPython June 25-27 Charleroi, Belgium

– Python11 at OSCON July 7-11 Portland, OR