Python - a Dynamic Programming Language. Guido van Rossum May 31, 2007

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2 Python - a Dynamic Programming Language Guido van Rossum May 31, 2007

6 What is Python? A dynamically typed general programming language Object-oriented, buzzword-compliant (sort of :-) Easy to learn, easy to read, easy to write, easy to use Almost executable pseudo-code :-) Mature: development started 18 years ago An Open Source project Trademarked by the Python Software Foundation Number 7 on the TIOBE list of programming languages Used by Google, NASA, Yahoo!, Microsoft, 6 Copyright 2007 Google Inc.

7 Application Areas Everything :-) Traditional scripting (e.g. system admininstration) Rapid prototyping Web apps, DB apps, GUI apps, XML apps Scientific computing 3rd party libraries for numerical processing, visualization replacing MATLAB in some areas Education introduction to programming courses One Laptop Per Child project uses Python 7 Copyright 2007 Google Inc.

8 Micro Tutorial >>> print 2** >>> def hello(name, n=1): # Greet name n times... for i in range(n):... print "Hello", name... >>> hello("beijing") Hello Beijing >>> hello("china", 2) Hello China Hello China >>> print " 故宫 " 故宫 >>> 8 Copyright 2007 Google Inc.

9 Micro Tutorial (Continued) >>> import urllib >>> f = urllib.urlopen(" >>> homepage = f.read() >>> counter = 0 >>> for line in homepage.splitlines():... if "Google" in line:... counter += 1... >>> print counter 3 >>> 9 Copyright 2007 Google Inc.

11 Brief Timeline Project started, name picked December 1989 First public release (USENET) February 1991 python.org website 1996 or 1997 Python 2.0 released 2000 Python Software Foundation created 2001 Python 2.4 released 2004 Python 2.5 released Copyright 2007 Google Inc.

12 Why I Designed Python ABC - teaching language created at CWI in Amsterdam designed in late 70s, early 80s (not by me!) I was on the implementation team from 82 through 86 had my own thoughts about its lack of success Amoeba - distributed microkernel OS almost completely, but not quite, unlike Unix only languages available were C and sh I decided to try to bridge the gap Other influences: Algol-60, Algol-68, C, Modula-3, Smalltalk, Icon but not Lisp at least not directly 12 Copyright 2007 Google Inc.

13 Original Design Goals Simple implementation (1 person) Typical Very-High-Level Language goals (see next slide) Cross-platform (hardware & OS) Readability and expressive power Easy to learn and remember; predictability Safety: bugs don t crash interpreter Don t compete with C; complement it! extensibility through C extension modules this makes Python an ideal glue language 13 Copyright 2007 Google Inc.

14 Standard VHLL Features Automatic memory management Small number of powerful data types Byte code interpreter (virtual machine) Built-in serialization (marshal, pickle) KISS (Keep It Simple, Stupid) Even indentation was borrowed! (from ABC, occam) lots of other stuff, too Python doesn t have "Not Invented Here" syndrome :-) 14 Copyright 2007 Google Inc.

15 Python s Big Ideas No type checking in the compiler Dynamic typing, static scoping Everything is an object Everything has a namespace (or several!) Everything can be introspected, printed System has few privileges over user Interactive prompt: >>> >>> Potential simplicity of implementation matters! 15 Copyright 2007 Google Inc.

16 Original Design Process Consider a desirable feature (either user feedback or my own needs discovered while using it) Only if there is absolutely no way to implement it as a library module or C extension, consider changing the compiler Make the absolutely minimal changes necessary to the compiler; reuse existing functionality as much as possible This gave us explicit self, for example 16 Copyright 2007 Google Inc.

17 Modern Design Process Pretty much the same, but also worrying about backwards compatibility Set the bar really high by only accepting new language features that will be of use to a wide variety of users Prevent repeating early mistakes, where sometimes shortcuts were taken that were too extreme, and had to be changed at great cost (e.g. int/long, classic classes) 17 Copyright 2007 Google Inc.

18 Counterforce: Readability No hack so clever or it must be readable! Require at least one of: Does it read naturally, like English? Does it resemble well-known math notation? Does it resemble a similar feature in another (popular) programming language? Is it a logical extension of existing syntax? (Of course this is highly subjective ) 18 Copyright 2007 Google Inc.

19 Community Interaction PEP: Python Enhancement Proposal Like JSR (Java), RFC (IETF) Though a bit less formal (smaller community) Not just for language changes Common APIs (e.g. db-api, WSGI) Sometimes library design (often not needed) Bookkeeping (e.g. release schedules) Typically not for performance enhancements Not a democracy! (Nor a dictatorship :-) Open Source has its own checks and balances Nobody has absolute power; we talk things over 19 Copyright 2007 Google Inc.

21 State of the Art Python 2.5 was released on September 19, 2006 Python on April 18, 2007 (pure bugfix release) Some language improvements: conditional expression (expr1 if condition else expr2) with-statement (with resource: code block) and more, e.g. relative import; generator improvements Library significantly improved, e.g.: ElementTree: better, faster XML processing SQLite: embedded database ctypes: call C functions directly Over 800 changes in subversion since Python 2.4! 21 Copyright 2007 Google Inc.

22 Other Python Implementations Jython: oldest, in 100% Pure Java, on JVM seamless integration with Java class libraries currently behind, but catching up (2.2 beta 2 is out!) IronPython: runs on.net (and Mono!) done by Jim Hugunin at Microsoft (he started Jython too!) MS shared source license (open source? seems so!) PyPy: experimental Python-in-Python European Community funded project mostly a research tool, not yet practical 22 Copyright 2007 Google Inc.

24 Python 3000: Python, Reloaded Python 3.0 = Python 3000 = Py3k Don t design a whole new language! Fix early design mistakes (many made in !) Allow incompatible changes (within reason) Get rid of deprecated f eatures first opportunity for big incompatibilities e.g. int division: 1/2 gives 0 in Python 2; 0.5 in Python 3 Consider what s the best feature going forward 24 Copyright 2007 Google Inc.

25 Python 3000 Highlights Unicode integral to the language (used to be optional) All text strings are Unicode Separate 'bytes' type for binary or encoded data Identifiers in code may use letters in any alphabet Text files automatically convert to/from encoded data Binary files read/write bytes, not strings UTF-16 vs. UTF-32: compile-time choice Linux vendors likely to choose UTF-32 Windows pretty much requires UTF Copyright 2007 Google Inc.

26 Python 3000 Highlights (Continued) Abstract Base Class support e.g. isinstance(x, Number), isinstance(x, Sequence) Function argument annotations e.g. def foo(x: Number, y: Sequence) -> Mapping Iterators instead of lists in many places e.g. range(), zip(), map(), filter() Better support for sets {1, 2, 3} instead of set([1, 2, 3]) dict.keys() returns a set (view) instead of a list 26 Copyright 2007 Google Inc.

27 Python 3000 Highlights (Continued) A single integer type named int behaves like long in Python 2.x (i.e. arbitrary precision) Print becomes a function easier to manipulate, substitute, refactor print >>sys.stderr, hello becomes print( hello, file=sys.stderr) New standard I/O library needed to implement the Unicode I/O features removes dependency on C stdio implementation 27 Copyright 2007 Google Inc.

28 Python 3000 Release Schedule Subject to change! First alpha: summer 2007 Final release: one year after first alpha Python 2.6 to be developed in parallel with 3.0: don t want users holding their breath waiting for is fully backwards compatible with also supports 3.0 compatibility mode some features backported from 3.0 warnings about features that will disappear or change 28 Copyright 2007 Google Inc.

21 Years of Python. From Pet Project to Programming Language of the Year. Guido van Rossum May 2011

21 Years of Python. From Pet Project to Programming Language of the Year. Guido van Rossum May 2011 21 Years of Python From Pet Project to Programming Language of the Year Guido van Rossum guido@python.org May 2011 Disclaimer I am speaking on my own behalf. My statements reflect my views only and do