Mailman 3 June 2013 - Python-ideas

argparse: --help-explain [options] ...
by anatoly techtonik 23 Jun '13

23 Jun '13

Inspired by QEMU: qemu -L . -m 128 -hda ReactOS.vmdk -net nic,model=ne2k_pci -net user -serial file:CON Can anybody tell what -L option does? QEMU help output is 6+ pages, and while it is not impossible to search through the content, I guess the first try for everybody is to try to lookup options visually. Going with every option one by one is rather tedious. So, the idea is that for such applications with extensive command line API, optparse (argparse or docopt) could provide --help-explain (or just --explain) option that parses command line and explains what it found. --help-explain [options] ... [options] ... --help-explain The option is position-independent to append it to existing command line. The explanation logic could be extensible, but that's a topic about state machine of valid option combinations. I am not sure argparse allows to manage that. However, docopt may be the saviour. -- anatoly t.

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Adding zope.testrunner test selections to unittest
by Barry Warsaw 22 Jun '13

22 Jun '13

(Maybe this should better go to the TIP mailing list?) One of the last things from zope.testrunner that I really rely on is its highly flexible support for test selection: https://pypi.python.org/pypi/zope.testrunner/4.4.0#test-selection Michael and I talked briefly about adding something like this to unittest's discover, where --pattern is a pale ghost of related functionality. Has anybody looked into this before? Is it something that we could feasibly add to Python 3.4? (and/or unittest2) -Barry

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unittest and warnings
by Giampaolo Rodola' 18 Jun '13

18 Jun '13

One of the features I like the most in the new unittest2 module is the possibility to skip tests and how they are included in the final result (e.g. FAILED (errors=2, failures=3, *skipped=5*)). After http://bugs.python.org/issue10093 it is not rare that different ResourceWarnings appear while running tests. Personally I consider these warnings as something which needs to be fixed so after I run tests I often scroll my console window back up to see whether there were warnings. Would it make sense for unittest module to keep track of them so that they get included in the final test result as it currently happens for skipped tests? Side note: unittest provides some "skip-related" APIs such unittest.skip*, TestResult.skipped and others but I don't think something similar would be necessary except maybe a TestResult.warnings list similar to TestResult.skipped. Regards, - Giampaolo https://code.google.com/p/pyftpdlib https://code.google.com/p/psutil https://code.google.com/p/pysendfile

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Re: [Python-ideas] unittest and warnings
by Vernon D. Cole 18 Jun '13

18 Jun '13

+1 for being able to get warnings counted, and optionally included with traceback. I am working on the django-mssql project, but I don't know django itself all that well. Two warnings are produced during the run of 4900 tests. (No, I did not key that incorrectly -- the test suite runs for hours on Windows.) I want to repair the code which causes the warnings -- but it is pretty hard to identify what caused them. Being able to get a full traceback, rather than a printout in the midst of the ...... would be really nice. -- Vernon Cole

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Elixir inspired pipe to apply a series of functions
by Jan Wrobel 17 Jun '13

17 Jun '13

Hello, I've recently stumbled upon a Joe Armstrong's (of Erlang) blog post that praises an Elixir pipe operator: http://joearms.github.io/2013/05/31/a-week-with-elixir.html The operator allows to nicely structure code that applies a series of functions to transform an input value to some output. I often end up writing code like: pkcs7_unpad( reduce(lambda result, block: result.append(block), map(decrypt_block, pairwise([iv] + secret_blocks)))) Which is dense, and needs to be read backwards (last operation is written first), but as Joe notes, the alternative is also not very compelling: decrypted_blocks = map(decrypt_block, pairwise([iv] + secret_blocks)) combined_blocks = reduce(lambda result, block: result.append(block)) return pkcs7_unpad(combined_blocks) The pipe operator nicely separates subsequent operations and allows to read them in a natural order without the need for temporary variables. Something like: [iv] + secret_blocks |> pairwise |> map, decrypt_block |> \ reduce, lambda result, block: result.append(block) |> \ pkcs7_unpad I'm not sure introducing pipes like this at the Python level would be a good idea. Is there already a library level support for such constructs? If not, what would be a good way to express them? I've tried a bit an figured out a following API (https://gist.github.com/wrr/5775808): Pipe([iv] + secret_blocks)\ (pairwise)\ (map, decrypt_block)\ (reduce, lambda result, block: result.append(block))\ (pkcs7_unpad)\ () The API is more verbose than the language level operator. I initially tried to overload `>>`, but it doesn't allow for additional arguments. It is also somehow smelly, because `()` returns a different type of value if it is invoked without an argument. Any suggestions how this could be improved? Best regards, Jan

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duck typing for io write methods
by Wolfgang Maier 16 Jun '13

16 Jun '13

Dear all, currently - and referring to Python 3 - the write methods of the different io module objects work on bytes and str objects only. The built-in functions print() and bytes(), on the other hand, use an arbitrary object's __str__ and __bytes__ methods to compute the str and bytes they should work with. Wouldn't it be more consistent and pythonic if the io write methods behaved the same way? Best, Wolfgang

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Add "htmlcharrefreplace" error handler
by Serhiy Storchaka 15 Jun '13

15 Jun '13

I propose to add "htmlcharrefreplace" error handler which is similar to "xmlcharrefreplace" error handler but use html entity names if possible. >>> '∀ x∈ℜ'.encode('ascii', 'xmlcharrefreplace') b'∀ x∈ℜ' >>> '∀ x∈ℜ'.encode('ascii', 'htmlcharrefreplace') b'∀ x∈&real;' Possible implementation: import codecs from html.entities import codepoint2name def htmlcharrefreplace_errors(exc): if not isinstance(exc, UnicodeEncodeError): raise exc try: replace = r'&%s;' % codepoint2name[ord(exc.object[exc.start])] except KeyError: return codecs.xmlcharrefreplace_errors(exc) return replace, exc.start + 1 codecs.register_error('htmlcharrefreplace', htmlcharrefreplace_errors) Even if do not register this handler from the start, it may be worth to provide htmlcharrefreplace_errors() in the html or html.entities module.

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Suprocess functionality partitioning
by anatoly techtonik 13 Jun '13

13 Jun '13

Something needs to be done about subprocess API, which got overly complicated. The idea is to have: shutil.run() - run command through shell, unsafe sys.run() - run command directly in operating system, ?safe Both should be API compatible (unblocking stdin/stdout read etc.). Currently, subprocess calls are unreadable in any Python code - many conditions makes its behaviour hard to predict and memorize. By partitioning shell and out-of-shell execution, the documentation will be easier to grasp and reference to. Maybe it will be even possible to add some 2D table of various subprocess states that affect behavior. -- anatoly t.

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Re: [Python-ideas] [Python-Dev] Unicode minus sign in numeric conversions
by Guido van Rossum 13 Jun '13

13 Jun '13

[Diverting to python-ideas, since this isn't as clear-cut as you think.] Why exactly is that expected behavior? What's the use case? (Surely you don't have a keyboard that generates \u2212 when you hit the minus key? :-) Is there a Unicode standard for parsing numbers? IIRC there are a variety of other things marked as "digits" in the Unicode standard -- do we do anything with those? If we do anything we should be consistent. For now, I think we *are* consistent -- we only support the ASCII representation of numbers. (And that's the only representation we generate as output as well -- think about symmetry too.) This page scares me: http://en.wikipedia.org/wiki/Numerals_in_Unicode --Guido On Sat, Jun 8, 2013 at 2:49 PM, Łukasz Langa <lukasz(a)langa.pl> wrote: > Expected behaviour: >>>> float('\N{MINUS SIGN}12.34') > -12.34 > > > Current behaviour: > Traceback (most recent call last): > ... > ValueError: could not convert string to float: '−12.34' > > > Please note: '\N{MINUS SIGN}' == '\u2212' > > -- > Best regards, > Łukasz Langa > > WWW: http://lukasz.langa.pl/ > Twitter: @llanga > IRC: ambv on #python-dev > > _______________________________________________ > Python-Dev mailing list > Python-Dev(a)python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: http://mail.python.org/mailman/options/python-dev/guido%40python.org -- --Guido van Rossum (python.org/~guido)

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Add \e escape code
by Steven D'Aprano 12 Jun '13

12 Jun '13

Should Python support \e in strings for the ESC control character, ASCII 0x1B (27)? \e is supported by Perl, PHP, Ruby, and although it is not standard C, gcc: http://gcc.gnu.org/onlinedocs/gcc-3.1/gcc/Character-Escapes.html I have the Python Pocket Reference, by Mark Lutz, 1st Edition from 1998, which lists \e as a string escape code. I don't know if that was a mistake, or if \e used to be supported prior to 1.5 but was then removed. -- Steven

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