Learning Python: Unit 1, Introduction (original) (raw)
Topics
● So what�s Python?
● Why do people use Python?
● A Python history lesson
● Advocacy news
● What�s Python good for?
● What�s Python not good for?
● Python technical features
● Python portability
So What�s Python?
�An open source, object-oriented, scripting language�
● An �open source� software project
♦ A BDFL plus a cast of thousands
♦ Mature infrastructure: PEPs, test suite, PSF
♦ Nonproprietary: you are not held hostage by a vendor (see VB, Apple)
♦ But you are dependent on _core developers_�at least on the leading edge
● An �object-oriented� language
♦ OOP is an option, but virtually required for larger projects
♦ OOP provides structure and code reuse in ways other tools do not: extendable code hierarchies
♦ But Python _isn�t just OO_�procedural, functional, OO
● A �scripting� language
♦ Control language: C/C++ libs, Com, Java/.NET, Soap/XML-RPC, Corba, RIA/AJAX/OpenStack�
♦ But Python is _general purpose_�not just for shell tools or simple programs
♦ Easier to use: typically 1/3 ~ 1/4 as much code as Java, C++ (syntax, typing, built-ins, libs)
Plus�
►General purpose
►Tactical or strategic
►Stand alone or embedded
►Very high-level, dynamic
Why Do People Use Python?
Software Quality
►Readable syntax: maintainable
►Coherent design, small set of interactions
►Simple enough to remember
►Art versus Engineering → maintenance, reuse
�You can do everything in Python that you can do in Perl, but you can read your code after you do it.�
Developer Productivity
►Smaller programs, flexible code (�agile�)
►Rapid turnaround, code reuse
►Both tactical and strategic roles
►Good in both boom and bust times
And other reasons�
►Program portability: portable system tools, �
►Component integration: reuse of libs, customization, �
►Vast application libraries: everything under the sun (but creates dependencies)
►Open source: no vendor tie-in (but still dependent on developers� whims)
Some Quotable Quotes (and some rebuttals)
■ �Python looks like it was designed,not accumulated.�
Though it�s gotten busier in recent years
■ �It bridges the gap between scripting languages and C.�
Though it�s grown more complex in recent years
■ �It�s as easy or as powerful as you want it to be.�
Though nontrivial software is never easy
■ �Python: less filling, tastes great. :-)�
Though it�s now 3-paradigms, 2-versions, feature-rich
■ �Python comes with batteries included.�
Though batteries can also be your weakest link
■ �Python fits your brain.�
Though it depends on your brain�
A Python History Lesson
● Created by Guido van Rossumin Amsterdam, 1990
♦ A Google employee for some time (then Dropbox)
♦ Google was/is largely Python code, as is YouTube
♦ Dropbox was/is mostly Python code on client+server
♦ Still Python�s BDFL, though the product of very many
♦ See Guido�s pages or search for more background
● USENET newsgroup started in 1994
♦ comp.lang.python, www.python.org
♦ 3rd party add-ons: PyPI, google.com, web search
● Python Software Foundation (PSF): O�Reilly, ActiveState, Google, Enthought, and many others
● First Python books appeared Fall, 1996, over 50 available by 2003, over 200 on amazon.com by 2012
● International following: US, Europe, Asia, Australia, etc.
● Community: users (1M+ guesstimate; 10M on Github);� user groups (see the list);� conferences (PyCon: 2,500 attendees by 2010s, OSCON, and alotmore)
● Named after 70s BBC comedy group �**Monty Python's Flying Circus**� (no, really)
♦ Shrubbery, Ni!, Brian, The Spanish Inquisition
♦ On the significance of Spam�
Advocacy News
The Latest�
Python continues to enjoy an active and vigorous community today.� It is generally considered to be one of the top 5 (or 10) most widely used programming languages in world, and is still growing in popularity by most metrics, including:
● Conference attendance: 2,500 or more recent PyCons
● Book sales: O'Reilly, Amazon
● User base success stories, quotes, and domains
● Web presence as tracked by the TIOBE index
● Other web presence trackers: Redmonk, PyPL
● Volume of open source contributions as measured by Ohloh.net
● Software support and resources
● And more: http://learning-python.com/books/about-python.html#resources
Noteworthy users
● Web services: Google, YouTube, Dropbox
● Animation: Industrial Light & Magic, ImageWorks, Disney, Pixar
● Financial: JP Morgan Chase, UBS, Getco, NYSE
● Games: Eve Online, Civilization IV
● Hardware Testing:Intel, Cisco, Hewlett-Packard, Seagate, Qualcomm, Micron
● Numerics: National Weather Service, Los Alamos, NASA
● P2P downloads:BitTorrent (32M DLs, 1/3 of all inettraffic!)
● Other: Calibre, iRobot, ESRI, NSA, IronPort,Red Hat, Jet Propulsion Lab, MIT compsci, Google App Engine, OLPC, OpenStack, Raspberry PI, �
Deployments
● Standard CPython(coded in C)
● IronPython for.NET/Mono (Microsoft), Python.net
● Jython for Java JVM
● PyPy (& Psyco): CPython optimized for speed
● Stackless: CPython for massive concurrency
● Numba, Cython: optimized solutions for numeric work
● Windows COM interface
● Web site and cloud frameworks: Django, AppEngine, �
● Mac OS X Cocoa integration
● Cellphone ports: Symbiam, Android, iOS, �
● RIAs: pyjamas (now pyjs), Silverlight, Flex, �
Group therapy
● Python user groups: everywhere today; see python.org user groups listand community page
Books
● Over 200 Python books available per amazon.com by 2012, English and other languages
Press
● Python.org�s quotesand success stories; and probably thousands more: search the web�
Education
● Computer Programming For Everybody (CP4E), edu-sig, tutors list, Raspberry PI, Code.org
Services
● Commercial support, training, books; distributions: py.org, ActiveState, Enthought, standard on Linux, Mac OS X
Jobs
● Thousands: see python.org job board or search the web, Dice.com, stackoverflow, etc.
Other
● PyCon conference attendance increases:
♦ 400-500 �05 vs 200-300 �04 ��
♦ to 1,000� in 2008-2010 ����
♦ to > 2,000 in 2012 Pycon
♦ 2,500 in all recent PyCons
What�s Python Good For?
General purpose:
� → Almost anything computers can do
● System programming: shell tools, test scripts
sockets, regex, POSIX calls, threads, streams
● Graphical user interfaces
Tk, wxPython, Qt,Gtk, Swing (Jython), RIAs (pyjamas/pyjs, etc.)
● Internet scripting
CGI, email, FTP, Telnet, Jythonapplets, XML-RPC, SOAP, PSP, mod_Python (Apache), RIAs, Django, Twisted, etc.
● Database programming
Persistent objects, ZODB, Oracle, Informix, Sybase, MySQL, Sqlite (standard lib), SQLObject,SQLAlchemy, �
● Component integration
Product customization and testing, embedded scripting, system front-ends
● Rapid Application Development
Prototype-and-migrate, fast turnaround, deliverable prototypes
● And more specific domains: general purpose
COM (PyWin32), Numeric programming (NumPy), Gaming (PyGame), graphics (OpenGL, Blender, Maya), AI, CORBA, CAD, data mining, instrumentation, language, ...
What�s Python Not Good For?
● Fast enough for most tasks as is
● Most real tasks run linked-in C code
● Exception: truly speed-critical components
● Solution: implement in C and export to Python
● Python is optimized for speed-of-development
● Python is designed for multi-language systems
● Example: Python Numeric Programming
● JIT (PyPy, Numba) may also improve speed
Python Technical Features (mostly for reference)
● No compile or link steps
Rapid development-cycle turnaround
● No type declarations
Programs are simpler, shorter, and flexible
● Automatic memory management
Garbage collection avoids bookkeeping code
● High-leveldatatypes and operations
Fast development using built-in object types
● Object-oriented programming
Code structuring and reuse, C++ integration
● Extending and embedding in C
Optimization, customization, system �glue�
● Classes, modules, exceptions
Modular �programming-in-the-large� support
● A simple, clear syntax and design
Readability, maintainability, ease of learning
● Dynamic loading of C modules
Simplified extensions, smaller binary files
● Dynamic reloading of Python modules
Programs can be modified without stopping
● Universal �first-class� object model
Fewer restrictions and special-case rules
● Interactive, dynamic nature
Incremental testing, runtime program coding/construction
● Access to interpreter information
Metaprogramming, introspective objects
● Wide interpreter portability
Cross-platform systems without ports
● Compilation to portable byte-code
Execution speed, protecting source-code
● Built-in interfaces to external services
O/S, GUI, persistence, DBMS, regular expressions...
● True �freeware�: Open Source software
May be embedded/shipped without copyright restrictions
Python Portability
● Core Language + Standard Library
♦ Windows, Linux, Macs, Unix
Nearly all flavors
Runs in desktop mode on Windows 8
Runs as a grown-up on Windows 10
Windows XP dropped as of 3.5
♦ Assorted platforms
Java (Jython)
.NET (IronPython)
JavaScript (pyjamas/pyjs)
Android (SL4A), Galaxy tablet, iOS, Raspberry PI
♦ And others, rare and nostalgic�
Cray supers, IBM mainframes, VxWorks realtime
PDAs: PalmOS,PocketPC, Zaurus
OS/2, VMS, Next, BeOS, QNX, Itanium
Amiga, AtariST
PlayStation, XBox,Gamecube
Nokia Symbian OS cellphones
Windows Mobile cellphones/PDAs
Ipods (if flashed)
● Platform-specific Extensions
♦ COM on Windows (PyWin32 extension)
♦ Cocoa on the Mac (Standard component)
♦ Other runtime libraries: Java, .NET, Javascript
● General Portability
♦ Bytecode is platform-neutral
♦ Portable GUIs: [tT]kinter, wxPython, PyQt, etc.: Windows, Linux, Macs, Unix
♦ Standard library system calls (most in module �os�)
��
On Apples and Oranges
| Versus | Python advantage | Description |
|---|---|---|
| Tcl , Lua | Power | Python better at �programming in the large�: module, OOP, exceptions, etc. |
| Perl | Coherence | Python has a readable, maintainable� syntax, fewer special variables, etc.� |
| Java | Simplicity Turnaround | Built-in objects, dynamic typing, etc.; can be freely shipped with products. |
| C++ | Simplicity Turnaround | Interpreted language turnaround; avoids C++ language complexity. |
| Smalltalk | Conventional | In Python, �if� statements are not message-receiver objects. |
| Ruby | Flexibility, maturity | Python more readable, more like C++: both procedural and OO (optional) |
| Scheme, Lisp | Conventional | Python�s syntax is closer to traditional languages like C and Pascal. |
| Visual Basic | Power, Portability | Python is powerful, cross-platform, and not controlled by one company (Python cannot be discontinued!) |
● But your mileage may vary
♦ Different language design goals
♦ Programmers matter too
♦ Many languages is a Good Thing
♦ Python coding can be too easy: design and brains still matter (beware the temptation to �hack�)
♦ Full-scale software development is not trivial in any language (though Python helps)
♦ Off page: hobbyists versus professionals, in Answer Me These Questions Three�
Summary: Why Python?
● It�s object-oriented
♦ Powerful OO support
♦ But OO is an option
● It�s free
♦ Can freely embed and ship in products
♦ Can even sell the source-code!
● It�s portable
♦ Runs everywhere: Unix, Windows, Mac,�
♦ Portable byte-code, portable Tkinter GUI interface
● It�s powerful
♦ Built-in types and operations
♦ Dynamic typing, libraries, modules, garbage collection, �
● It�s mixable
♦ Python/C, Python/C++, Python/Java, COM
● It�s easy to use (relative to others)
♦ Fast turnaround after changes
♦ A simple language and syntax
● It�s easy to learn (relative to others)
♦ For developers and product customers
→ Quality and� Productivity
A scripting language doesn't have to look like one
(The following was posted to the rec.humor.funny USENET newsgroup by L. Hastings, and is reprinted here with the original author�s permission.)
This has been percolating in the back of my mind for a while. It's a scene from The Empire Strikes Back, reinterpreted to serve a valuable moral lesson for aspiring programmers.
EXTERIOR: DAGOBAH--DAY
With Yoda strapped to his back, Luke climbs up one of the many thick vines that grow in the swamp until he reaches the Dagobah statistics lab. Panting heavily, he continues his exercises--grepping, installing new packages, logging in as root, and writing replacements for two-year-old shell scripts in Python.
YODA: ���� Code!� Yes.� A programmer's strength flows from code
������������� maintainability.� But beware of Perl. Terse syntax... more
������������� than one way to do it... default variables.� The dark side of
������������� code maintainability are they.� Easily they flow, quickto join
������������� you when code you write.�If once you start down the dark
������������� path, forever will it dominate your destiny, consume you
������������� it will.
LUKE: Is Perl better than Python?
YODA: ���� No... no... no.� Quicker, easier, more seductive.
LUKE: But how will I know why Python is better than Perl?
YODA: ���� You will know.� When your code you try to read six
������� months from now.