SobrePython

What do you think about moving this to http://www.python.org/cgi-bin/moinmoin/ - it would be better ontopic there and also reach a bigger audience. -- ThomasWaldmann DateTime(2004-10-11T08:57:04Z)

If will not have problem I would like that stayed here, but is been necessary... -- LeonardoGregianin (2004-10-11 13:54 UTC-4)

Introdução

O desenvolvimento do Python começou em 1990 na CWI (Instituto de Matemática e Ciência da Computação) em Amsterdam na Holanda por Guido van Rossum, e continuou liderada pela Python Software Foundation (http://www.python.org/psf).

Python has a full set of string operations (including regular expression matching), and frees the user from most hassles of memory management. These and other features make it an ideal language for prototype development and other ad-hoc programming tasks.

Python also has some features that make it possible to write large programs, even though it lacks most forms of compile-time checking: a program can be constructed out of a number of modules, each of which defines its own name space, and modules can define classes which provide further encapsulation. Exception handling makes it possible to catch errors where required without cluttering all code with error checking.

A large number of extension modules have been developed for Python. Some are part of the standard library of tools, usable in any Python program (e.g. the math library and regular expressions). Others are specific to a particular platform or environment (for example, UNIX, IP networking, or X11) or provide application-specific functionality (such as image or sound processing).

Python also provides facilities for introspection, so that a debugger or profiler (or other development tools) for Python programs can be written in Python itself. There is also a generic way to convert an object into a stream of bytes and back, which can be used to implement object persistency as well as various distributed object models.

O que é Python

O Python é uma linguagem de programação portável, pode ser utilizada em plataforma Windows, Linux e UNIX. É Interpretada e Interativa. Orientada a objetos, aliás, tudo em Python é um objeto. Tipada dinamicamente não se declarara o tipo de variáveis, retornos de funções e parâmetros, os tipos são identificados de acordo com o uso que fazemos deles. O controle de bloco de comandos é feito apenas por alinhamento (Endentada), não há delimitadores do tipo Begin e End do Pascal ou { e } da linguagem C. Oferece tipos de dados de alto nível como strings de verdade, dicionários (também conhecido por hashes ou arranjos associativos), listas, tuplas, classes, etc. Aceita outros paradigmas de programação bastantes úteis, como a programação modular, para evitar a "poluição" de nomes e a programação funcional, que descreve mais facilmente determinadas estruturas. A sintaxe é fácil de ser compreedida e rápida de ser desenvolvida; a construção dos tipos de dados são de alto-nível. Python pode ser extendida em módulos de compilação como C e C++. Os módulos de extensão podem definir novas funções e variáveis, também como novos tipos de objetos. Python é semelhante a outras linguagens interpretadas como Tcl, Perl, Scheme or Java.

Often, programmers fall in love with Python because of the increased productivity it provides. Since there is no compilation step, the edit-test-debug cycle is incredibly fast. Debugging Python programs is easy: a bug or bad input will never cause a segmentation fault. Instead, when the interpreter discovers an error, it raises an exception. When the program doesn't catch the exception, the interpreter prints a stack trace. A source level debugger allows inspection of local and global variables, evaluation of arbitrary expressions, setting breakpoints, stepping through the code a line at a time, and so on. The debugger is written in Python itself, testifying to Python's introspective power. On the other hand, often the quickest way to debug a program is to add a few print statements to the source: the fast edit-test-debug cycle makes this simple approach very effective.

Filosofia do Python

'''The Zen of Python'''

Bonito é melhor que feio.  
Explícito é melhor que implícito.  
Simples é melhor que complexo.  
Complexo é melhor que complicado.  
*Flat is better than nested.
Escasso é melhor que denso.  
Legibilidade conta.
Casos especiais não são especiais bastante para quebrar as regras.  
*Although practicality beats purity.
Erros nunca deveriam passar silenciosamente.
A menos que explicitamente silenciasse.
Em face a ambigüidade, recuse a tentação para adivinhar.
Deveria haver um -- e preferentemente só um -- modo óbvio para fazer isto.  
Embora aquele modo pode não ser óbvio a menos que você seja holandês.
Agora é melhor que nunca.  
Embora nunca é freqüentemente melhor que *right* agora.  
Se a implementação é dura para explicar, isto é uma idéia ruim.
Se a implementação é fácil para explicar, pode ser uma idéia boa.  
Namespaces são uma grande idéia -- façamos mais desses!

A linguagem

• Endentação
• Identificadores
• Tipos de dados
• Operadores
• Estrutura de dados
• Controles de fluxos
• Funções
• Módulos e pacotes
• Exceções
• Classes
• Métodos

Interpretador Python

Implementações

Comparações de várias implementações do Python retirada de http://www.intertwingly.net/blog/2004/10/04/Comparing-Pythons

Metodologia

• I started with Mical's test cases as they were small micro unit tests.
• I removed any test that failed using CPython 2.3.4. Some tests were designed to raise an exception, and unhandled exceptions are likely to vary between implementations.
• I ran each test on pie-thon, ast2past, and pirate on the latest Parrot from CVS on Debian. I also ran each test on jython on Java 1.4.2 and iron-python on .Net 1.1.4322, both on WindowsXP.
• I marked each output as pass if output as compared to the CPython implementation on the same platform was byte for byte identical.
• I marked each output as pass* if the outputs differed only in leading or trailing spaces. There were a fair number of these.
• All other outputs were marked as FAIL. Where possible, I tried to capture stderr.
• Click on the links to see the source of the test and the outputs.

Resultados

-- Os códigos dos testes estão na página original.

Módulos

• Pygame

Comparações entre interfaces gráficas (GUI)

• PyGTK
• PyQT
• wxPython
• Tkinter

Licença

The Python license imposes very few restrictions on what you can do with Python. Most of the source code is copyrighted by the Python Software Foundation (PSF). A few files have a different copyright owner, but the same license applies to all of them.

In layman's language, here are the primary features of Python's license. The following descriptions are not legal advice; read the full text of the license and consult qualified professional counsel for an interpretation of the license terms as they apply to you.

• Python é absolutamente livre, even for commercial use (including resale). You can sell a product written in Python or a product that embeds the Python interpreter. No licensing fees need to be paid for such usage.
• The Open Source Initiative has certified the Python license as Open Source, and includes it on their list of open source licenses.
• There is no GPL-like "copyleft" restriction. Distributing binary-only versions of Python, modified or not, is allowed. There is no requirement to release any of your source code. You can also write extension modules for Python and provide them only in binary form.
• However, the Python license is compatible with the GPL, according to the Free Software Foundation.
• You cannot remove the PSF's copyright notice from either the source code or the resulting binary.

Comparações entre linguagens

Guido van Rossum escreveu que Python is often compared to other interpreted languages such as Java, JavaScript, Perl, Tcl, or Smalltalk. Comparisons to C++, Common Lisp and Scheme can also be enlightening. In this section I will briefly compare Python to each of these languages. These comparisons concentrate on language issues only. In practice, the choice of a programming language is often dictated by other real-world constraints such as cost, availability, training, and prior investment, or even emotional attachment. Since these aspects are highly variable, it seems a waste of time to consider them much for this comparison.

Java

Python programs are generally expected to run slower than Java programs, but they also take much less time to develop. Python programs are typically 3-5 times shorter than equivalent Java programs. This difference can be attributed to Python's built-in high-level data types and its dynamic typing. For example, a Python programmer wastes no time declaring the types of arguments or variables, and Python's powerful polymorphic list and dictionary types, for which rich syntactic support is built straight into the language, find a use in almost every Python program. Because of the run-time typing, Python's run time must work harder than Java's. For example, when evaluating the expression a+b, it must first inspect the objects a and b to find out their type, which is not known at compile time. It then invokes the appropriate addition operation, which may be an overloaded user-defined method. Java, on the other hand, can perform an efficient integer or floating point addition, but requires variable declarations for a and b, and does not allow overloading of the + operator for instances of user-defined classes.

For these reasons, Python is much better suited as a "glue" language, while Java is better characterized as a low-level implementation language. In fact, the two together make an excellent combination. Components can be developed in Java and combined to form applications in Python; Python can also be used to prototype components until their design can be "hardened" in a Java implementation. To support this type of development, a Python implementation written in Java is under development, which allows calling Python code from Java and vice versa. In this implementation, Python source code is translated to Java bytecode (with help from a run-time library to support Python's dynamic semantics).

PHP

Python e PHP são interpretadas, linguagens de alto-nível com tipagem dinâmicas, códigos aberto, são suportadas por grandes comunidades na internet, são fáceis de aprender (comparadas ao Java), são fáceis para serem extendidas a C, C++ e Java, são extremamente portáveis.

Mas Python não existe várias habilidades que PHP existem como:

• syntax from C and Perl, with lots curly braces and dollar signs.
• the 'switch' statement and 'do ... while' construct.
• increment and decrement and assignment operators (assignment is a statement only in Python).
• the ternary operator/statement (... ? ... : ...).
• schizophrenic tableau of function names. The builtin library has a wide variety of naming conventions. There are no namespaces, so functions often have prefixes to denote their source (but often not). Functions are often placed into classes to simulate namespaces.
• a very casual language, where globals are often used to pass arguments, all variables are "set" (to NULL), and a somewhat weak type system (not to be confused with dynamic types).
• an expedient (commonly installed) environment.

• aliases ('$a =& $b' means that when $b changes, $a changes also).

• one array type that doubles as a list and a dictionary. Dictionary keys are iterated in their original order.

E, também, o PHP não tem inúmeras habilidades que Python possui:

• a general purpose programming language (not just for the web)
• indentation is used to mark out block structure rather than curly braces
• namespaces and modules
• a small core
• very clear, concise, and orthogonal syntax
• it is self documenting with docstrings and pydoc
• keyword arguments to functions and methods, easy support for default arguments
• true object orientation and 'first class' classes and functions
• classes are used extensively in the standard library
• a notion of private attributes
• multiple inheritance
• object-oriented file handling
• method chaining
• excellent introspection
• everything is a reference! (references are painful in PHP)
• one 'del' statement for all data types. PHP has 'unset' for variables and something else for array members.
• consistent case sensitivity (PHP does for variables, but not functions)
• a simple array slicing syntax
• lambdas and other builtin functional programming constructs
• iterators
• structured exception handling
• operator overloading
• SWIG? integration
• threading
• an excellent profiler, plus several debuggers and IDEs

• lots of high-level data types (lists, tuples, dicts, mx.DateTimes, NumPy arrays, etc.)

• differentiation between arrays (lists) and associative arrays (dictionaries).
• cached byte-code compilation (available for $980 in PHP!)
• a standardized database API
• support for all major GUI frameworks
• strong internationalization and UNICODE support
• maturity, stability and upward-compatibility.
• tends to lead to much more scalable applications -- importing modules is safer than textually including code as in PHP: global variables are not used to exchange information.

Retirada de: http://wiki.w4py.org/pythonvsphp.html

Javascript

Python's "object-based" subset is roughly equivalent to JavaScript. Like JavaScript (and unlike Java), Python supports a programming style that uses simple functions and variables without engaging in class definitions. However, for JavaScript, that's all there is. Python, on the other hand, supports writing much larger programs and better code reuse through a true object-oriented programming style, where classes and inheritance play an important role.

Perl

Python and Perl come from a similar background (Unix scripting, which both have long outgrown), and sport many similar features, but have a different philosophy. Perl emphasizes support for common application-oriented tasks, e.g. by having built-in regular expressions, file scanning and report generating features. Python emphasizes support for common programming methodologies such as data structure design and object-oriented programming, and encourages programmers to write readable (and thus maintainable) code by providing an elegant but not overly cryptic notation. As a consequence, Python comes close to Perl but rarely beats it in its original application domain; however Python has an applicability well beyond Perl's niche.

Tcl

Like Python, Tcl is usable as an application extension language, as well as a stand-alone programming language. However, Tcl, which traditionally stores all data as strings, is weak on data structures, and executes typical code much slower than Python. Tcl also lacks features needed for writing large programs, such as modular namespaces. Thus, while a "typical" large application using Tcl usually contains Tcl extensions written in C or C++ that are specific to that application, an equivalent Python application can often be written in "pure Python". Of course, pure Python development is much quicker than having to write and debug a C or C++ component. It has been said that Tcl's one redeeming quality is the Tk toolkit. Python has adopted an interface to Tk as its standard GUI component library.

Tcl 8.0 addresses the speed issuse by providing a bytecode compiler with limited data type support, and adds namespaces. However, it is still a much more cumbersome programming language.

Smalltalk

Perhaps the biggest difference between Python and Smalltalk is Python's more "mainstream" syntax, which gives it a leg up on programmer training. Like Smalltalk, Python has dynamic typing and binding, and everything in Python is an object. However, Python distinguishes built-in object types from user-defined classes, and currently doesn't allow inheritance from built-in types. Smalltalk's standard library of collection data types is more refined, while Python's library has more facilities for dealing with Internet and WWW realities such as email, HTML and FTP.

Python has a different philosophy regarding the development environment and distribution of code. Where Smalltalk traditionally has a monolithic "system image" which comprises both the environment and the user's program, Python stores both standard modules and user modules in individual files which can easily be rearranged or distributed outside the system. One consequence is that there is more than one option for attaching a Graphical User Interface (GUI) to a Python program, since the GUI is not built into the system.

C++

Almost everything said for Java also applies for C++, just more so: where Python code is typically 3-5 times shorter than equivalent Java code, it is often 5-10 times shorter than equivalent C++ code! Anecdotal evidence suggests that one Python programmer can finish in two months what two C++ programmers can't complete in a year. Python shines as a glue language, used to combine components written in C++.

Common Lisp e Scheme

These languages are close to Python in their dynamic semantics, but so different in their approach to syntax that a comparison becomes almost a religious argument: is Lisp's lack of syntax an advantage or a disadvantage? It should be noted that Python has introspective capabilities similar to those of Lisp, and Python programs can construct and execute program fragments on the fly. Usually, real-world properties are decisive: Common Lisp is big (in every sense), and the Scheme world is fragmented between many incompatible versions, where Python has a single, free, compact implementation.

Exemplos de comparações

Esses exemplos são apenas de linguagens mais conhecidas e todos imprimem na tela a mensagem hello world. Os scripts foram retirados de http://www2.latech.edu/~acm/helloworld/.

Python

print 'hello world'

Java

  public class HelloWorld {
  public static void main(String[] args) {
     System.out.println("Hello World"); 
  }
}

PHP

<? print("Hello World") ?>  

Java Script

<script language="JavaScript">
  alert("Hello World");
</script>

Perl

print "Hello World\n";

Tcl

wm title . "Hello world!"

frame .h -borderwidth 2
frame .q -borderwidth 2
button .h.hello -text "Hello world" \
        -command "puts stdout \"Hello world!\"" -cursor gumby
button .q.quit -text "Quit" -command exit -cursor pirate

pack .h -side left
pack .q -side right
pack .h.hello
pack .q.quit

Small Talk

Transcript show:'Hello World';cr 

C++

#include <iostream.h>
  int main()
    {
    cout << "Hello, World\n";
    return -1;
    }

LISP

; LISP
(DEFUN HELLO-WORLD ()
                  (PRINT (LIST 'HELLO 'WORLD)))

Scheme

(define hello-world
  (lambda ()
    (begin
      (write 'Hello-World)
      (newline)
      (hello-world))))

Elogios

Industrial Light & Magic

"Python plays a key role in our production pipeline. Without it a project the size of Star Wars: Episode II would have been very difficult to pull off. From crowd rendering to batch processing to compositing, Python binds all things together," said Tommy Burnette, Senior Technical Director, Industrial Light & Magic.

"Python is everywhere at ILM. It's used to extend the capabilities of our applications, as well as providing the glue between them. Every CG image we create has involved Python somewhere in the process," said Philip Peterson, Principal Engineer, Research & Development, Industrial Light & Magic.

Google Inc.

"Python has been an important part of Google since the beginning, and remains so as the system grows and evolves. Today dozens of Google engineers use Python, and we're looking for more people with skills in this language." said Peter Norvig, director of search quality at Google, Inc.

NASA

"NASA is using Python to implement a CAD/CAE/PDM repository and model management, integration, and transformation system which will be the core infrastructure for its next generation collaborative engineering environment. We chose Python because it provides maximum productivity, code that's clear and easy to maintain, strong and extensive (and growing!) libraries, and excellent capabilities for integration with other applications on any platform. All of these characteristics are essential for building efficient, flexible, scalable, and well-integrated systems, which is exactly what we need. Python has met or exceeded every requirement we've had," said Steve Waterbury, Software Group Leader, NASA STEP Testbed.

EVE Online

"Python enabled us to create EVE Online, a massive multiplayer game with a scale never before seen in the industry, in record time. EVE Online server cluster, servers close to 10.000 simultaneous players in a shared space simulation, most of which is created in Python. The flexibilities of Python have enabled us to quickly improve the game experience based on player feedback," said Hilmar Veigar Petursson, chief technology officer of CCP, the developers of EVE Online.

Home Gain

"Home Gain maintains its commitment to continual improvement through rapid turnaround of new features and enhancements. Python supports this short time-to-market philosophy with concise, clear syntax and a powerful standard library. New development proceeds rapidly, and maintenance of existing code is straightforward and fast," said Geoff Gerrietts, Software Engineer, Home Gain.com.

Thawte Consulting

"Python makes us extremely productive, and makes maintaining a large and rapidly evolving codebase relatively simple," said Mark Shuttleworth.

University of Maryland

"I have the students learn Python in our undergraduate and graduate Semantic Web courses. Why? Because basically there's nothing else with the flexibility and as many web libraries," said Prof. James A. Hendler.

EZTrip.com

"The travel industry is made up of a myriad supplier data feeds all of which are proprietary in some way and are constantly changing. Python repeatedly has allowed us to access, build and test our in-house communications with hundreds of travel suppliers around the world in a matter of days rather then the months it would have taken using other languages. Since adopting Python 2 years ago, Python has provided us with a measurable productivity gain that allows us to stay competitive in the online travel space," said Michael Engelhart, CTO of EZTrip.com.

Paul Graham

"Paul Graham has posted a new article to his website that he called "The Python Paradox" which refines the statements he made in "Great Hackers" about Python programmers being better hackers than Java programmers. He basically says that since Python is not the kind of language that lands you a job like Java, those who learn it seek more than simply financial benefits, they seek better tools. Very interesting read."

Eric S. Raymond

http://www.linuxjournal.com/article.php?sid=3882

Histórias de sucesso

Indústria

• Industrial Light & Magic (http://www.ilm.com), produz filmes da série Star Wars, usando extensivamente Python para computação gráfica nos processos de produção dos filmes.

• Google Inc. (http://www.google.com), o maior site de busca da internet, é desenvolvido em Python.

• Yahoo! (http://www.yahoo.com) usa Python para o site de grupos.

• The Inktomi (http://www.inktomi.com) usa Python para seu site de busca.

• IBM (http://www.ibm.com) e consequentemente Philips (http://www.philips.com), entre outras linguagens e aplicativos, usam Python para criar a lógica da prática de negócios para a produção de ferramentas de controle de aplicativos.

• Disney (http://www.disney.com) usa Python para produção de aplicativos de animação.

• Wolfgang Puck Soups (http://www.wolfgangpucksoup.com) usa Python na infra-estrutura de seus bens de consumo duráveis fabricando pela companhia.

• Red Hat Linux (http://www.redhat.com) usa Python para instalação, configuração e gerenciamento de pacotes.

• Real Networks (http://www.real.com) usa extensivamente Python em testes do sistema e em testes cliente/servidor para plataformas de apoio.

• Strakt (http://www.straky.com) usa Python para construir a próxima geração de seu rapidíssimo ambiente colaborativo.

• Object Domain (http://www.objectdomain.com) é uma implementação em Java, compreendendo ferramenta CASE e usando Python para suporte.

• Totally Games (http://www.totallygames.com) usa Python para muitas características de jogos como Star Trek Bridge Commander.

• The7 Afilias INFO (http://www.afilias.info) usa Python como primeira linguagem, uso genérico de alto nível com aplicações .COM desde 1985.

• The Viacom Television Stations Group (http://www.paramountstations.com) usa Python para vários sites de estações de TV.

• BEA (http://www.bea.com) usa Python em testes de softwares e-comércio.

• American Greetings (http://www.americangreetings.com) usa Python para servir milhões de cartões-saudação todos os dias.

• Plone Inc. (http://www.plone.org) usa Python para desenvolver seu conhecido software colaborativo Plone.

• Zope Corporation (http://www.zope.org) usa Python para diversa aplicações como ZOBD (Banco de Dados), CMF (aplicações de baixo nível), etc.

Ciência

• NASA (http://www.nasa.gov) usa Python em muitos dos seus projetos, incluindo um sistema CAD/CAM e um módulo gráfico usado em missões de planejamento do espaço.

• The National Institutes of Health (http://www.ncrr.nih.gov) e Case Western Rerserve University (http://www.cwru.edu/) são building cutting-edge genetic analysis software with Python.

• The National Weather Service (http://www-md.fsl.noaa.gov/eft) usa Python para preparar previsões meteorológicas. Python também é usado para este propósito no Swedish Meteorological and Hydrological Institute e na TV Sueca TV4.

• Lawrence Livermore National Laboratories (http://www.llnl.gov) é baseado em um novo ambiente numérico de engenharia em Python, substituindo uma outra linguagem em funcionamento a mais de 10 anos.

• The Theoretical Physics Division at Los Alamos National Laboratory (http://bifrost.lanl.gov/MD/MD.html) usa Python para controlar códigos de grande escala de física em super-computadores paralelos, servidores e clusters.

Governo

• The US Navy (http://www.navy.mil) usa Python e Zope para seu sistema de website.

• The US Dept. of Agriculture (http://www.usda.gov) usa Python e Zope para grande quantidade de colaborações.

Bibliografia

• Como Pensar como um Cientista de Computação em Python (Em tradução) http://pensarpython.incubadora.fapesp.br/portal

• http://ibiblio.org/obp/thinkCSpy/ -> Livro original em Inglês

• Python: Guia de Consulta Rápida - Marco Catunda

Tutoriais

• http://async.com.br/projects/python/pnp/python.html

• http://pygtk.org/pygtk2tutorial-es/index.html

• http://async.com.br/faq/pygtk/index.py?req=index

• http://pythonbrasil.com.br/moin.cgi/OsvaldoSantanaNeto <- python vs.java

• http://portaldaprogramacao.com/index_linguagem.asp?c=22

Módulos implementações

• http://sourceforge.net/projects/pywikipediabot

• http://www.strout.net/python

• http://www.pygame.org

Outros Links

• http://pyzine.com

• http://python.org

• http://planetpython.org

• http://pythonbrasil.com.br

• http://pygtk.org

• http://python.org/doc/Comparisons.html

• http://idi.ntnu.no/~mlh/python/praise.html

• http://scriptbrasil.com.br/forum/index.php?showforum=38

• http://python-in-business.org/success/

• http://pythonology.org

• http://www.intertwingly.net

• http://twistedmatrix.com/wiki/python/FrontPage Python Wiki Wiki