State of the Python Union OSCON Portland, Oregon July 29, 2004 Guido van Rossum Elemental Security, Inc. [email protected] [email protected].

State of thePython Union

OSCONPortland, Oregon

July 29, 2004

Guido van Rossum

Elemental Security, Inc.

[email protected]@elementalsecurity.com

July 29, 2004 © 2004 Guido van Rossum 2


Keynote Overview

• PSF Grants

• Release status

• Python 2.4:

– Generator expressions

– Decorators

– Other news

• Beyond Python 2.4

• Miscellaneous remarks

• Cute demos

• Question time



PSF Grants

• Grants for projects related to:– the further development of Python

– Python-related technology

– educational resources

• Proposals to be submitted by October 1, 2004– proposals granted by November 1, 2004

– work to be completed by October 30, 2005

• Up to $40,000 available in total

• See python.org for details and how to submit



Release Status

• Python 2.2 is resting ("pining for the fjords")

• Python 2.3 is actively maintained

– 2.3.4 came out in May

– 2.3.5 planned later this year

– Anthony Baxter is release manager

• I am out of the loop!

• Python 2.4 alpha 2 to be released next week

– 2.4 final release expected Q4 2004

– Anthony Baxter is release manager

• I am mostly out of the loop!



Generator Expressions

• Consider: print sum(x**2 for x in range(10))

• Compare:

– total = 0for x in range(10): total += x**2print total

• Factor out summing algorithm for reuse

• Concentrate on providing input without distractions

• Easily switch between different data processors

– "accumulator functions"

– "iterator algebra" a.k.a. pipelining


Why Generator Expressions?

• Notation is immediately understandable

• Avoids building up a list of intermediate results– This is especially important if:

• intermediate results are large; or

• there are many intermediate results; or

• the source is an infinite sequence– e.g. from itertools: count(), cycle(), repeat()

• the consumer doesn't consume all results

• an interactive user is waiting for the initial results

• List comprehensions are a special case:– [f(x) for x ...] is syntactic sugar for list(f(x) for x ...)

• (in Python 2.4 there are some corner cases with different semantics; these will be fixed in 3.0)

• won't go away


The Generator Expression Debate

• Someone noticed an "implementation flaw":– a = []

for f in [math.sin, math.cos, math.tan]: a.append(f(x) for x in range(10))

– for iterator in a: for x in iterator: print x, print

– Prints math.tan(x) series three times! (f is bound late)

• Should we try to fix this? (If so, how?)

• NO! Genexps are for immediate consumption– fix the docs / tutorials / examples

– delayed use would be expert/advanced use anyway• working solutions are quite bearable



Decorators

• Consider (introduced in python 2.2):

– class C: def func(args): ...100 lines of body text... func = staticmethod(func)

• Problem with this syntax:

– programmer may forget to add the staticmethod() call

– reader may miss the staticmethod() call

• Proposed solution:

– class C: ***DECORATOR SYNTAX*** func(args): body


What Is a Decorator?

• A decorator is a meta-function:

– input is a callable or descriptor (implements __get__)

– output is a callable or descriptor

– examples: classmethod, staticmethod, (property)

• Other use cases:

– metadata (e.g. author, version, deprecation)

– processing rules (e.g. SPARK's grammar rules)

– support for external language bindings (ObjC, C#)

– framework annotations (e.g. PIKE)

• Ideally, decorators should be chainable


Decorator Syntax Candidates

• Java 1.5:– @decorator and/or @decorator(key=value, ...)

• C#:– [decorator, decorator, ...]

• Other proposals from Python developers:– [decorator, decorator, ...] in various other positions

– *[decorators]*

– <decorators>

– [as decorators]

– other keywords or symbols


Decorator (Ab)uses

• def funcattrs(**kwds): def helper(func): func.__dict__.update(kwds) return func return helper

• Example with Java 1.5-derived syntax:

– @funcattrs(grammar="blah", author="GvR")def blah(args): body

• Example with C#-derived syntax:

– [funcattrs(grammar="blah", author="GvR")]def blah(args): body


Which Decorator Syntax?

• All styles have their disadvantages:

– @decorator

• looks unpythonic (?)

– [deco, deco, ...] prefix

• ambiguous syntax

• and doesn't work in interactive interpreter

– [deco, deco, ...] after arguments

• hides the decorators too much

• is awkward for long decorators

– Other proposals look arbitrary (even 'as')

• In 2.4a2, we'll implement @decorator

– if everybody hates it, we'll revisit in a3 or b1



What Else is New in 2.4?

• Faster (e.g. tklife.py gains ~20% speed-up)

• New built-in set types: set and frozenset

• Unifying int and long: now always the same results– except repr() still returns an 'L' suffix for longs

• New builtins: sorted(), reversed()

• Keyword arguments to list.sort(): cmp, key, reverse

• eval() takes arbitrary mapping for locals (only)

• None is a constant (assigning to it is a syntax error)

• Decimal floating point data type (module decimal)

• Email parser rewritten from scratch

• CJKCodecs integrated (East-Asian codecs)

• New module cookielib (client-side cookie handling)

• Windows distribution now built using MSVC++ 7.1



Beyond Python 2.4

• Python 2.5.........2.9:

– gradual improvements

– new library modules/packages

– backwards-compatible changes

– implement more existing PEPs

– performance work

– implementation internals work (e.g. AST branch)

– experiment with features proposed for Python 3.0

• There will not be a Python 2.10

– but 2.5 ... 2.9 may be released in parallel with 3.0



Python 3.0 (a.k.a. Python 3000)

• I had a Python 3.0 slide, but it's all day-dreaming

• 3.0 is my excuse for putting off thorny issues

• Has been "about 3 years away" since 2000 :-)

• I need to retire to be able to work on this

• Python 3.0 : 2.x isn't anything like Perl 6.0 : 5.x

• But it will be incompatible



Miscellaneous Remarks

• The sincerest form of flattery is imitation– Python borrows from many other languages

– Now Ruby, Groovy, Prothon borrow from Python

• Python runs on Nokia Series 60 phones– Public release not yet certain

– Would open up Nokia platform to more developers

• Write your secure programs in Python– 1 security defect per 1000 lines across languages

– But in Python it takes fewer lines :-)

• Community issues– Why is there still no Python equivalent of CPAN?

– There are too many projects doing X; how to choose?



Cute Demos

• ElementClass

– Simple way to describe (some) XML documents

– Get attributes and subelements as Python attributes

– Parses string or stream into tree in memory

– Renders to string or stream

– Not (yet) released, developed for Elemental Security

• Conway's Game of Life / Damian's cellular automata


Question Time

State of the Python Union OSCON Portland, Oregon July 29, 2004 Guido van Rossum Elemental Security, Inc. [email protected] [email protected].

Documents

body slide

pipelining slide

b1 slide

bearable slide

chainable slide

decorator abuses

decorator andor

python developers