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

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July 29, 2004© 2004 Guido van Rossum 3 Keynote Overview PSF Grants Release status Python 2.4: –Generator expressions –Decorators –Other news Beyond Python 2.4 Miscellaneous remarks Cute demos Question time

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July 29, 2004© 2004 Guido van Rossum 5 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

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July 29, 2004© 2004 Guido van Rossum 7 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 Q –Anthony Baxter is release manager I am mostly out of the loop!

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July 29, 2004© 2004 Guido van Rossum 9 Generator Expressions Consider: print sum(x**2 for x in range(10)) Compare: –total = 0 for x in range(10): total += x**2 print 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

July 29, 2004© 2004 Guido van Rossum 10 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

July 29, 2004© 2004 Guido van Rossum 11 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

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July 29, 2004© 2004 Guido van Rossum 13 Decorators Consider (introduced in python 2.2): –class C: def func(args): 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

July 29, 2004© 2004 Guido van Rossum 14 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

July 29, 2004© 2004 Guido van Rossum 15 Decorator Syntax Candidates Java 1.5: C#: –[decorator, decorator,...] Other proposals from Python developers: –[decorator, decorator,...] in various other positions –*[decorators]* – –[as decorators] –other keywords or symbols

July 29, 2004© 2004 Guido van Rossum 16 Decorator (Ab)uses def funcattrs(**kwds): def helper(func): func.__dict__.update(kwds) return func return helper Example with Java 1.5-derived syntax: author="GvR") def blah(args): body Example with C#-derived syntax: –[funcattrs(grammar="blah", author="GvR")] def blah(args): body

July 29, 2004© 2004 Guido van Rossum 17 Which Decorator Syntax? All styles have their disadvantages: 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 –if everybody hates it, we'll revisit in a3 or b1

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July 29, 2004© 2004 Guido van Rossum 19 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) parser rewritten from scratch CJKCodecs integrated (East-Asian codecs) New module cookielib (client-side cookie handling) Windows distribution now built using MSVC++ 7.1

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July 29, 2004© 2004 Guido van Rossum 21 Beyond Python 2.4 Python : –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 may be released in parallel with 3.0

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July 29, 2004© 2004 Guido van Rossum 23 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

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July 29, 2004© 2004 Guido van Rossum 25 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?

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July 29, 2004© 2004 Guido van Rossum 27 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

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Question Time