Mailman 3 June 2013 - Python-Dev

eval and triple quoted strings
by Walter Dörwald June 18, 2013

June 18, 2013

Hello all! This surprised me: >>> eval("'''\r\n'''") '\n' Where did the \r go? ast.literal_eval() has the same problem: >>> ast.literal_eval("'''\r\n'''") '\n' Is this a bug/worth fixing? Servus, Walter

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Re: [Python-Dev] cpython: Issue #3329: Add new APIs to customize memory allocators
by Antoine Pitrou June 18, 2013

June 18, 2013

On Sat, 15 Jun 2013 00:44:11 +0200 (CEST) victor.stinner <python-checkins(a)python.org> wrote: > http://hg.python.org/cpython/rev/6661a8154eb3 > changeset: 84127:6661a8154eb3 > user: Victor Stinner <victor.stinner(a)gmail.com> > date: Sat Jun 15 00:37:46 2013 +0200 > summary: > Issue #3329: Add new APIs to customize memory allocators > > * Add a new PyMemAllocators structure > * New functions: > > - PyMem_RawMalloc(), … [View More]

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Problem with pydoc script in PEP 405 venvs
by Vinay Sajip June 17, 2013

June 17, 2013

Issue #18224 (http://bugs.python.org/issue18224) highlights a problem on Windows with the pydoc script provided with venvs created by pyvenv. On POSIX, the script is named pydoc and causes no problems: on Windows, it is called pydoc.py and this causes problems because it shadows the stdlib pydoc module. Possible solutions: 1. Remove the pydoc script altogether from created venvs, on Windows but also on POSIX (for consistency). 2. Rename the pydoc script on both Windows and POSIX (e.g. to … [View More]

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Writing Extensions for Python 3 in Windows
by Aditya Avinash June 17, 2013

June 17, 2013

Hi. This is the last place where I want to ask a question. I have searched for lots of tutorials and documentation on the web but, didn't find a decent one to develop extensions for Python 3 using a custom compiler (mingw32, nvcc). Please help me. PS: Don't point me to Python Documentation. It is not good for beginners. It doesn't elaborate about calls and implementation. -- Aditya Avinash Atluri

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Backports galore
by Łukasz Langa June 16, 2013

June 16, 2013

Now we have (at least) the following libraries backported from 3.2+ to older versions of Python by members of the core team: - configparser - enum34 - singledispatch - subprocess32 - unittest2 There are also unofficial backports like billiard (multiprocessing). I would be happy if all those were more discoverable by the community at large. Having a single namespace for backports would be great but my spidey sense forebodes large flocks of bike sheds flying that way. Can we put links to … [View More]

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Clean way in python to test for None, empty, scalar, and list/ndarray? A prayer to the gods of Python
by Martin Schultz June 16, 2013

June 16, 2013

As much as I love python, the following drives me crazy, and I would wish that some future version would come up with a more consistent approach for this. And please don't reply with "Too bad if you don't know what type your data are..." - if I want to implement some generic functionality, I want to avoid constrains on the user where not absolutely necessary, and I believe this approach is truely pythonic. OK - here comes the problem set. These are in fact several related issues. Clearly, a … [View More]solution exists for each of them, but you will have to admit that they are all very different in style and therefore unnecessarily complicate matters. If you want to write code which works under many circumstances, it will become quite convoluted. 1. Testing for None: From what I read elsewhere, the preferred solution is `if x is None` (or `if not x is None` in the opposite case). This is fine and it works for scalars, lists, sets, numpy ndarrays,... 2. Testing for empty lists or empty ndarrays: In principle, `len(x) == 0` will do the trick. **BUT** there are several caveats here: - `len(scalar)` raises a TypeError, so you will have to use try and except or find some other way of testing for a scalar value - `len(numpy.array(0))` (i.e. a scalar coded as numpy array) also raises a TypeError ("unsized object") - `len([[]])` returns a length of 1, which is somehow understandable, but - I would argue - perhaps not what one might expect initially Alternatively, numpy arrays have a size attribute, and `numpy.array([]).size`, `numpy.array(8.).size`, and `numpy.array([8.]).size` all return what you would expect. And even `numpy.array([[]]).size` gives you 0. Now, if I could convert everything to a numpy array, this might work. But have you ever tried to assign a list of mixed data types to a numpy array? `numpy.array(["a",1,[2,3],(888,9)])` will fail, even though the list inside is perfectly fine as a list. 3. Testing for scalar: Let's suppose we knew the number of non-empty elements, and this is 1. Then there are occasions when you want to know if you have in fact `6` or `[6]` as an answer (or maybe even `[[6]]`). Obviously, this question is also relevant for numpy arrays. For the latter, a combination of size and ndim can help. For other objects, I would be tempted to use something like `isiterable()`, however, this function doesn't exist, and there are numerous discussions how one could or should find out if an object is iterable - none of them truly intuitive. (and is it true that **every** iterable object is a descendant of collections.Iterable?) 4. Finding the number of elements in an object: From the discussion above, it is already clear that `len(x)` is not very robust for doing this. Just to mention another complication: `len("abcd")` returns 4, even though this is only one string. Of course this is correct, but it's a nuisance if you need to to find the number of elements of a list of strings and if it can happen that you have a scalar string instead of a 1-element list. And, believe me, such situations do occur! 5. Forcing a scalar to become a 1-element list: Unfortunately, `list(77)` throws an error, because 77 is not iterable. `numpy.array(77)` works, but - as we saw above - there will be no len defined for it. Simply writing `[x]` is dangerous, because if x is a list already, it will create `[[77]]`, which you generally don't want. Also, `numpy.array([x])` would create a 2D array if x is already a 1D array or a list. Often, it would be quite useful to know for sure that a function result is provided as a list, regardless of how many elements it contains (because then you can write `res[0]` without risking the danger to throw an exception). Does anyone have a good suggestion for this one? 6. Detecting None values in a list: This is just for completeness. I have seen solutions using `all` which solve this problem (see [question #1270920][1]). I haven't digged into them extensively, but I fear that these will also suffer from the above-mentioned issues if you don't know for sure if you are starting from a list, a numpy array, or a scalar. Enough complaining. Here comes my prayer to the python gods: **Please** - add a good `isiterable` function - add a `size` attribute to all objects (I wouldn't mind if this is None in case you don't really know how to define the size of something, but it would be good to have it, so that `anything.size` would never throw an error - add an `isscalar` function which would at least try to test if something is a scalar (meaning a single entity). Note that this might give different results compared to `isiterable`, because one would consider a scalar string as a scalar even though it is iterable. And if `isscalar` would throw exceptions in cases where it doesn't know what to do: fine - this can be easily captured. - enable the `len()` function for scalar variables such as integers or floats. I would tend to think that 1 is a natural answer to what the length of a number is. [1]: http://stackoverflow.com/questions/1270920/most-concise-way-to-check-whethe… [View Less]

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PEP 442 accepted
by Benjamin Peterson June 15, 2013

June 15, 2013

I (and Guido) are accepting PEP 442 (Safe object finalization) on the condition that finalizers are only ever called once globally. Congratulations to Antoine on writing yet another PEP that deeply touches the core language in a way that everyone can agree is an improvement.. I look forward to reviewing the code. -- Regards, Benjamin

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Allow calling PyMem_Malloc() without the GIL held in Python 3.4
by Victor Stinner June 14, 2013

June 14, 2013

Hi, I would like to remove the "GIL must be held" restriction from PyMem_Malloc(). In my opinion, the restriction was motived by a bug in Python, bug fixed by the issue #3329. Let me explain why. The PyMem_Malloc() function is a thin wrapper to malloc(). It returns NULL if the size is lager than PY_SSIZE_T_MAX and have a well defined behaviour for PyMem_Malloc(0) (don't return NULL). So it is surprising to read in Include/pymem.h: "The GIL must be held when using these APIs." The reason is … [View More]

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Re: [Python-Dev] [Python-checkins] cpython: Closes issue 17947. Adds PEP-0435 (Enum, IntEnum) to the stdlib.
by Brett Cannon June 14, 2013

June 14, 2013

Ethan, did you forget to run ``hg add`` before committing? If not then why the heck did we argue over enums for so long if this was all it took to make everyone happy? =) On Fri, Jun 14, 2013 at 3:31 AM, ethan.furman <python-checkins(a)python.org>wrote: > http://hg.python.org/cpython/rev/fae92309c3be > changeset: 84117:fae92309c3be > parent: 84115:af27c661d4fb > user: Ethan Furman <ethan(a)stoneleaf.us> > date: Fri Jun 14 00:30:27 2013 -0700 &… [View More]

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Summary of Python tracker Issues
by Python tracker June 14, 2013

June 14, 2013

ACTIVITY SUMMARY (2013-06-07 - 2013-06-14) Python tracker at http://bugs.python.org/ To view or respond to any of the issues listed below, click on the issue. Do NOT respond to this message. Issues counts and deltas: open 4042 (+18) closed 25946 (+41) total 29988 (+59) Open issues with patches: 1795 Issues opened (41) ================== #17947: Code, test, and doc review for PEP-0435 Enum http://bugs.python.org/issue17947 reopened by ncoghlan #18159: ConfigParser getters not … [View More]

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