🌐 Mailman 3 December 2016 - Python-list - python.org

perl + python tutorial available for download
by Xah May 7, 2017

May 7, 2017

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by uomiocenekidd＠gmail.com April 12, 2017

April 12, 2017

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Re: strange behaviour when writing a large amount of data on stdout
by bokr＠oz.net April 11, 2017

April 11, 2017

On Wed, 23 Nov 2005 18:18:34 +0100, "Fredrik Lundh" <fredrik(a)pythonware.com> wrote: >Manlio Perillo wrote: > >> >>>>> print data >> >> >> >> Traceback (most recent call last): >> >> File "xxx", line xxx, in ? >> >> print data >> >> IOError: [Errno 12] Not enough space >> > >> >errno 12 is ENOMEM (that is, the system did not have enough memory >> >to finish an operation). >> >> However I think the error message is not a good one. >> Better a "Not enough memory" > >the message text is provided by the operating system (or rather, by >the C library). I'm not sure rewriting error messages is a good thing... > >(if Python itself runs out of memory, it'll raise a MemoryError instead) > Maybe there's a bare except: somewhere blocking earlier & perhaps more informative messages? If windows has been running a long time (a few days or a week may be long ;-) it may get fragmented in some smallish memory arena reserved for special things (I forgot what versions, but I wouldn't be surprised if something still had s specialized limit). Does the program involve dynamic generation of desktop icons by any chance? Especially a lot of large true-color ones? I have some faint inkling of some correlation of that and memory problems with still huge amounts of heap memory available. Has the OP rebooted and just run the offending program alone? BTW, if the OP wants to find out how much memory is on the windows system, the amount of memory probably shows in the "about" window of the task manager (the NT task manager will give you a scrolling real-time graph of different kinds of memory usage as well). Also if the OP has windows word editor (probably winword.exe will start it from the console command line), the "about" dialog may have a "system info ..." button that will show memory and a lot more. What that button runs is C:\Program Files\Common Files\Microsoft Shared\MSInfo\MSINFO32.exe on my system. Since it's accessible from Word, I wouldn't think it would be too unsafe to run, but I guess the OP might not want to start diagnostic things on arbitrary devices etc., if that's accessible from his session. Regards, Bengt Richter

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Question about abstract base classes and abstract properties -- Python 2.7
by Gerald Britton Jan. 11, 2017

Jan. 11, 2017

I was rereading the 2.7 docs about abstract base classes the other day. I found this line in the usage section of the abc.abstractproperty function: "This defines a read-only property; you can also define a read-write abstract property using the ‘long’ form of property declaration:" along with an example. so I copied the example and put in a little surrounding code: from abc import ABCMeta, abstractproperty class C(object): __metaclass__ = ABCMeta def getx(self): pass def setx(self, value): pass x = abstractproperty(getx, setx) class D(C): @property def x(self):self._x d = D() print(d) When I ran this, I expected an exception, since I defined a read/write abstract property but only implemented the read operation. However, the example runs fine. That is the class D can be instantiated without error. Of course I cannot set the property since I didn't implement that part. Now, If I don't implement the property at all, I can' instantiate the class. I get: "TypeError: Can't instantiate abstract class D with abstract methods x" which is what I would expect. What I don't understand is why I don't get a similar error when I implement the read operation for the property but not the write operation. If this actually doesn't work (catching the non-implementation at instantiation time), then why is it documented this way. To me at least the doc implies that it *will* raise on the missing write property implementation (otherwise, what's the point of the example?) Is this a doc bug, an ABC bug or just me? (I've been known to be buggy from time to time!) -- Gerald Britton

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how to create IPictureDisp objects with python?
by Felix Jan. 5, 2017

Jan. 5, 2017

i try to host an activex control in my program . the control has a picture property which only accepts "IPictureDisp" interfaces. does anybody know how to create IPictureDisp objects? thanks.

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Simulating int arithmetic with wrap-around
by Steve D'Aprano Jan. 4, 2017

Jan. 4, 2017

It's easy to simulate integer arithmetic with wrap-around for *unsigned* ints. For example, imagine a four-bit integer (0 through 15): # Addition py> (7 + 8) & 0xF 15 py> (7 + 9) & 0xF 0 py> (7 + 10) & 0xF 1 # Multiplication py> (7 * 2) & 0xF 14 py> (7 * 3) & 0xF 5 py> (7 * 4) & 0xF 12 And in general, for any operator ⊗, and a and b both in the range 0 through 2**N-1, we can simulate unsigned N-bit integer arithmetic with: a⊗b & (2**N - 1) (I think this works for all the arithmetic operators, and the bitwise operations. The bitmask & 2**N-1 is not needed for the bitwise operations except for left-shift.) How about *signed* integers? 7 + 1 => -8 7 + 2 => -7 7 + 7 => -2 7 * 2 => -2 7 * 3 => 5 7 * 4 => -4 Again, assume both operands are in range for an N-bit signed integer. What's a good way to efficiently, or at least not too inefficiently, do the calculations in Python? Signed arithmetic also has some gotchas. For example, -x is not necessarily defined, nor is abs(x). Thanks, -- Steve “Cheer up,” they said, “things could be worse.” So I cheered up, and sure enough, things got worse.

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Re: Cleaning up conditionals
by BartC Jan. 2, 2017

Jan. 2, 2017

On 30/12/2016 21:20, Deborah Swanson wrote: > I've already learned one neat trick to collapse a conditional: > > a = expression1 if condition else expression2 > > Here I have a real mess, in my opinion: > > if len(l1[st]) == 0: > if len(l2[st]) > 0: > l1[st] = l2[st] > elif len(l2[st]) == 0: > if len(l1[st]) > 0: > l2[st] = l1[st] This doesn't make sense. The main block is executed when len(l1[st]) is 0, but you're testing for len(l1[st])>0 in the last if statement (which can't see the assignment to l1[st], so can never be true). Try writing it out on paper using A and B instead l1[st] and l2[st] as they look confusing. You might also be evaluating len(l2[st]) twice. -- Bartc

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learning and experimenting python.
by einstein1410＠gmail.com Jan. 2, 2017

Jan. 2, 2017

Hello everyone, I am the new comer and learner of python. I have a doubt that when I type python and press enter it shows a prompt like >>> But why it is >>> ? Is there any special reason? Why it is not setted as @,& or any other special characters?

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Re: Cleaning up conditionals
by Jussi Piitulainen Jan. 1, 2017

Jan. 1, 2017

Deborah Swanson writes: > Is it possible to use some version of the "a = expression1 if > condition else expression2" syntax with an elif? And for expression1 > and expression2 to be single statements? That's the kind of > shortcutting I'd like to do, and it seems like python might be able to > do something like this. I missed this question when I read the thread earlier. The answer is simply to make expression2 be another conditional expression. I tend to write the whole chain in parentheses. This allows multi-line layouts like the following alternatives: a = ( first if len(first) > 0 else second if len(second) > 0 else make_stuff_up() ) a = ( first if len(first) > 0 else second if len(second) > 0 else make_stuff_up() ) Expression1 and expression2 cannot be statements. Python makes a formal distinction between statements that have an effect and expressions that have a value. All components of a conditional expression must be expressions. A function call can behave either way but I think it good style that the calls in expresions return values.

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mentor training python Romania with certification
by blue Jan. 1, 2017

Jan. 1, 2017

Hi. I'm from Romania. I need to update my skils under python. I need to find one mentor ( class, training ) to obtain one certified under python language. Cătălin George Feștilă

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