Re: Instance method for converting int to str - str() and __str__()
In a message of Fri, 02 Oct 2015 23:35:28 -0700, neubyr writes: >I was wondering if there is any resource that explains why certain methods >like str() and type() were implemented the way they are, rather than >.to_string() or .type() instance/object methods. > >I find instance/object methods more intuitive for this cases, but I am >wondering why it wasn't implemented it like that. > >I know there are equivalents like __str__() and __class__ , but passing >object to str() or type() seems more popular. > >Any resources for reading or some background information would be helpful. > >- CS > >-- >https://mail.python.org/mailman/listinfo/python-list > start reading here: https://www.python.org/download/releases/2.2/descrintro/ and keep searching and reading about type-class unification in Python. The answer is, because types and classes used to be very different things, and you _couldn't_. Laura -- https://mail.python.org/mailman/listinfo/python-list
Re: Pyserial and Ubuntu Linux kernel 3.13.0-65-generic
In a message of Fri, 02 Oct 2015 22:36:23 -, Rob Gaddi writes: >So, this is odd. I'm running Ubuntu 14.04, and my system did a kernel >upgrade from the repository from 3.13.0-63-generic to 3.13.0-65-generic. >And pyserial (2.7, installed through pip) stopped working. > >Specifically, when I make read() calls on a Serial object, I get the error > >serial.serialutil.SerialException: device reports readiness to read but >returned no data (device disconnected?) > >This comes from the PosixSerial.read() method in serialposix.py, and >seems to be a result of the select.select call screwing up. > >I reboot under 3.13.0-63-generic. My code works. I reboot under >3.13.0-65-generic. My code doesn't. Implication would seem to be that >somehow between these kernel versions, the select() logic in the serial >driver changed. This happens regardless of whether the serial port is >real, FTDI USB-UART, or Prolific USB-UART. > >Can anyone else confirm? Also, who do I try to report this one to? > >Thanks, >Rob > >-- >Rob Gaddi, Highland Technology -- www.highlandtechnology.com >Email address domain is currently out of order. See above to fix. >-- >https://mail.python.org/mailman/listinfo/python-list I think you have this bug https://bugs.launchpad.net/ubuntu/+source/linux/+bug/460857 or rather, you like the behaviour that ubuntu thinks is buggy, which never got fixed, and don't like that it changed to be what ubuntu thinks is correct in .65. I'd talk to the pyserial issue tracker as the people there ought to be well aware of this problem, and then see if talking to ubuntu is the right thing to do. Laura -- https://mail.python.org/mailman/listinfo/python-list
Re: Pyserial and Ubuntu Linux kernel 3.13.0-65-generic
In a message of Sat, 03 Oct 2015 11:07:04 +0200, Laura Creighton writes: >In a message of Fri, 02 Oct 2015 22:36:23 -, Rob Gaddi writes: >>So, this is odd. I'm running Ubuntu 14.04, and my system did a kernel >>upgrade from the repository from 3.13.0-63-generic to 3.13.0-65-generic. >>And pyserial (2.7, installed through pip) stopped working. >> >>Specifically, when I make read() calls on a Serial object, I get the error >> >>serial.serialutil.SerialException: device reports readiness to read but >>returned no data (device disconnected?) >> >>This comes from the PosixSerial.read() method in serialposix.py, and >>seems to be a result of the select.select call screwing up. >> >>I reboot under 3.13.0-63-generic. My code works. I reboot under >>3.13.0-65-generic. My code doesn't. Implication would seem to be that >>somehow between these kernel versions, the select() logic in the serial >>driver changed. This happens regardless of whether the serial port is >>real, FTDI USB-UART, or Prolific USB-UART. >> >>Can anyone else confirm? Also, who do I try to report this one to? >> >>Thanks, >>Rob >> >>-- >>Rob Gaddi, Highland Technology -- www.highlandtechnology.com >>Email address domain is currently out of order. See above to fix. >>-- >>https://mail.python.org/mailman/listinfo/python-list > >I think you have this bug >https://bugs.launchpad.net/ubuntu/+source/linux/+bug/460857 > >or rather, you like the behaviour that ubuntu thinks is buggy, >which never got fixed, and don't like that it changed to be >what ubuntu thinks is correct in .65. > >I'd talk to the pyserial issue tracker as the people there ought >to be well aware of this problem, and then see if talking to >ubuntu is the right thing to do. > >Laura >-- >https://mail.python.org/mailman/listinfo/python-list I think I said that poorly. What I think happened is that ubuntu made some changes to fix this problem, and along the way they managed to break things for you, and maybe all pyserial users. But I would talk to the pyserial people about that. Laura -- https://mail.python.org/mailman/listinfo/python-list
Re: Pyserial and Ubuntu Linux kernel 3.13.0-65-generic
With better searching, I find this bug. https://bugs.launchpad.net/ubuntu/+source/linux-lts-trusty/+bug/1501345 Looks like that's the real one. Laura -- https://mail.python.org/mailman/listinfo/python-list
Re: Instance method for converting int to str - str() and __str__()
On 10/3/2015 2:35 AM, neubyr wrote: I was wondering if there is any resource that explains why certain methods like str() and type() These are classes. Calling a class calls the class construction and initialization functions. These return an instance of the class. While reading the tutorial, read the library reference, chapter 2. Chapter 4 is also extremely important to read. -- Terry Jan Reedy -- https://mail.python.org/mailman/listinfo/python-list
Re: Check if a given value is out of certain range
On Fri, 2 Oct 2015 07:45 am, John Gordon wrote:
> In <87r3le1ht3@elektro.pacujo.net> Marko Rauhamaa
> writes:
[...]
>> Wouldn't
>
>>x < 0 or 10 < x
>
>> be even more visual?
>
> I don't know what you mean by "more visual".
>
> In my opinion, when comparing a variable to a constant, it's more natural
> to have the variable on the left and the constant on the right, so that's
> one strike against this code.
>
> Another strike is that the code isn't consistent with itself; it puts the
> variable on the left in the first comparison, then swaps to the right for
> the second comparison.
The alternative is equally inconsistent: for one comparison it uses less
than, for the other it uses greater than.
I find this discussion about the relative readability of
not 0 <= x <= 10 #1
versus
0 < x or x > 10 #2
0 < x or 10 < x
to be a good example of people's propensity to invent so-called "rational"
justifications for irrational preferences. Honestly, all these people
claiming that reading #1 takes them "slightly more effort" than reading #2,
or vice versa. Really? You've done an objective test of this? I don't think
so.
We know from UI testing in other fields that people's *self-reported*
efficiency and their *actual* efficiency are almost completely
uncorrelated. Back in the DOS versus Macintosh days, when mice were new,
DOS users consistently reported that using a mouse was too slow and
inefficient compared to the keyboard, but actual objective measurements of
the time that they took to do tasks showed the opposite.
E.g. subjects were asked to do some task, using the keyboard and then again
using the mouse, and (let's say) it actually took them 3 minutes to do it
via keyboard and 2 minutes via mouse, they reported that using the keyboard
commands was much more efficient, fast and easy.
Whether you have #1 or either variation of #2, the time it takes to read and
comprehend the expression is likely to be of the order of a few dozen
milliseconds, plus or minus a few dozen milliseconds. I expect the
variation will be nearly as great as the average time. (But of course, I
haven't done objective studies either.)
Anyone who has done high-school level maths should be familiar with the
notation `0 <= x <= 10`, read as "x between 0 and 10". (Anyone who is not
can hardly claim to be fluent in Python -- that's like claiming to be
fluent in English while not knowing where and how to use an exclamation
mark.)
If you want to check for the opposite, x not between 0 and 10, the natural
way to do so is with `not`: `not 0 <= x <= 10`. If you prefer `x < 0 or x >
10` for whatever reason, that's fine too. Some people prefer pizza, some
prefer kebabs... inventing (spurious) arguments of (imaginary) efficiency
("It takes me half a second less time to chew each mouthful of burger
compared to kebab") is unnecessary. But we do love the argument from
efficiency.
Frankly, as a profession, we programmers are lousy at prioritising. We write
pages and pages of convoluted, inconsistent, hard to understand code that
can sometimes take hours or even days to comprehend well enough to make
even a minor change, while spending dozens of person-hours arguing about
which expression saves them a microsecond or two of reading time. Yay us!
--
Steven
--
https://mail.python.org/mailman/listinfo/python-list
Re: Check if a given value is out of certain range
On 03/10/2015 11:29, Steven D'Aprano wrote: On Fri, 2 Oct 2015 07:45 am, John Gordon wrote: I find this discussion about the relative readability of not 0 <= x <= 10 #1 versus 0 < x or x > 10 #2 0 < x or 10 < x to be a good example of people's propensity to invent so-called "rational" justifications for irrational preferences. Honestly, all these people claiming that reading #1 takes them "slightly more effort" than reading #2, or vice versa. Really? I find #1 straightforward (although I'm bothered by the lack of parentheses as I would parse that as (not 0). Presumably, this does actually mean not (0<=x<=10).) But I spent a minute looking at #2, and I'm still not sure that it expresses the same thing. I would have written #2 as: x<0 or x>10 -- Bartc -- https://mail.python.org/mailman/listinfo/python-list
Re: Instance method for converting int to str - str() and __str__()
On Sat, 3 Oct 2015 04:35 pm, neubyr wrote: > I was wondering if there is any resource that explains why certain methods > like str() and type() were implemented the way they are, rather than > .to_string() or .type() instance/object methods. There is a FAQ that might help with this question: https://docs.python.org/2/faq/design.html In early Python, some objects (like ints, floats, tuples, None) had no methods at all, so you couldn't have None.to_string() and expect it to work. There was no base class for the entire object hierarchy, so no method they could inherit: every class would have to re-implement their own to_string method. But even today, when all objects have methods and all inherit from object, having functions instead of methods for some tasks makes good sense. It allows us to write functions that operate by a protocol, rather than purely by inheritance, and it helps guarantee consistent naming. For example, let's look at conversion to bool. Should that method be called .bool, .boolean, .to_bool, .truthify, ... ? Different classes that don't inherit from each other may make different choices. By having a built-in function (technically, a class, but the difference doesn't matter here) called bool, that ensures one standard way to convert to bool. How does bool() work? As a built-in function, it can (in theory) include optimizations that aren't available to a method, for example it could look like this pseudocode: def bool(obj): if obj is None: return False if obj is a number: return obj != 0 ... which may be faster than calling obj.bool() since it doesn't have to search the inheritance chain (remember that method resolution in Python happens at runtime, not compile-time). Of course, the built-in bool needs to know how to deal with custom classes that aren't built-in. For that, we have a *protocol* that tells the built-in functions how to deal with new, unknown classes. The most basic protocol is to call a specified "dunder" method. Dunder stands for: Double leading and trailing UNDERscores and refers to those methods __str__, __add__, __radd__, etc. that you so often see. All dunder names are reserved for use by Python, so you should never use them yourself, and especially never invent your own. bool() is a good example of a protocol because it is more complex than just a single method call. It looks something like this: # Python 3 version def bool(x): # possible optimizations for built-ins here... # now deal with everything else T = type(x) if hasattr(T, '__bool__'): flag = T.__bool__() if flag in (True, False): return flag else: raise TypeError elif hasattr(T, '__len__'): return T.__len__() != 0 else: return True bool(x) ignores methods defined on the instance x itself, and goes straight to the class object (saving a runtime lookup). If the dunder method does not return an actual boolean, it raises an error. And if the object doesn't define a __bool__ method, it falls back on __len__, and if it doesn't define __len__ either, it could in principle have other fallbacks, but in practice just returns a default value. (Of course, the actual built-in bool may be written in C, not Python, but that's besides the point.) So you should never call dunder methods such as __str__ yourself, always call the wrapper. Chances are very good that the function form will contain optimizations that are unavailable to you, will perform pre-processing or post-processing, catch exceptions, or error-check the result. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
Footnotes in ReST
I have a document written in Restructured Text format, and I use lots of footnotes: blah blah blah [1]_ and blah blah blah [2]_. blah blah [3]_ blah ... blah blah blah blah [999]_. .. [1] fe .. [2] fi .. [3] fo ... .. [999] fum I need to add a footnote between [2] and [3], but I don't want to have to renumber the following 997 footnotes by hand. Is there something I can do, within the syntax of ReST itself, to help? -- Steven -- https://mail.python.org/mailman/listinfo/python-list
Re: Footnotes in ReST
On Sat, Oct 3, 2015 at 9:39 PM, Steven D'Aprano wrote: > I need to add a footnote between [2] and [3], but I don't want to have to > renumber the following 997 footnotes by hand. Is there something I can do, > within the syntax of ReST itself, to help? Now that they're all numbered manually? Not sure. But if you know in advance you're going to have that kind of thing, there are other ways to do footnotes: https://hg.python.org/peps/file/tip/pep-0498.txt https://www.python.org/dev/peps/pep-0498/ Otherwise, I'd look at scripting the 997-footnote changes. It shouldn't be too hard to script - will probably take only twice as long as doing it manually would have... ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Check if a given value is out of certain range
Actually, the fact that adults have more difficulty processing negations is one of the earliest things proven experimentally in experimental psychology. Clark, H., & Chase, W. (1972). On the process of comparing sentences against pictures. Cognitive Psychology, 3, 472–517. is one of the most heavily cited experiments in the field. The question is _why_? The early assumption was that the negation is conceptually more difficult. People think logically, and a negation is a harder sentence to construct. Recently, this idea has come to be questioned: see http://www.google.se/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB0QFjAAahUKEwisvv_6lKbIAhXo8XIKHX32BKE&url=http%3A%2F%2Flangcog.stanford.edu%2Fpapers_new%2Fnordmeyer-2015-underrev.pdf&usg=AFQjCNEaPmluLtZs6aeAHgnyCCLEDazJdg which I shortened to: http://bit.ly/1OOfK46 It seems that people tend to hear what they expect to hear, and that effect overwhelms any 'this is harder to constuct logically' effect. Also, the 'mouse is quicker' experiment was rather more nuanced than you reported. It seems when measuring 'what is faster' the cognitive load is important. Time seems to go faster when you are thinking harder about something, than when you are not. (i.e. how did my coffee get cold? I just started hacking on this thing?) It seems that mouse editing was less of a cognitive load than typing, for the people studied, thus they reported that keyboard was faster, when it wasn't for them. But the experiment was replicated among secretaries who had superior typing skills (and used emacs a lot). For a lot of them, moving text by mouse was not faster than using keyboard macros. But the limiting factor seemed to be 'how hard did I have to think about it' -- if you move things by keyboard macro without thinking, then you won't report that it takes you time, and you won't accurately report how long it takes to do the task. Thus for this experiment, the conclusion was that people were a whole lot better at telling 'how hard did this make me think' than 'how long did it take me to do the job'. Also, when you changed the requirements to 'reformat text all day long' a huge number of people could get a lot more work done using emacs than using the mouse editor. We ran both of these experiemnts in the coputer graphics lab at the University of Toronto as a joint csc/psych exp in the mid 1980s, and our conclusion at the time was that, for 'all day long' sorts of tasks what was most important was boredom. Once the subject got bored with the task, it took longer. For me the experiment was wonderful for another reason. The University of Toronto has long believed that their secretaries weren't intelligent enough to use emacs, and had gone to particular effort to design an easier editor for them to use. But the secretaries of the Political Science department, who used to come down to the department of Zoology (where I worked) to use our pdp-11/44 for text formating, and me (the undergraduate they hired to help Zoologists format their graduate theses prior to having them phototypeset) for advice, once saw me fix a problem by writing an emacs macro, and hauling their document into emacs and using it. They were entranced. And wondered if I could teach them how to do it. I thought, fine enough, and so taught classes in how to use emacs to about 6 of them for 3 nights a week one summer. And it turned out that everybody, including one sweet lady whose powers of reasoning was seriously sub par, learned how to use emacs. She learned mostly by rote, but she could do it. And the first two weeks of learning how to write macros was very hard. I learned a lot about how not to teach things in that class. :) So a good bit of the problem was lack of skill in the teacher. But once we started on writing them for real life tasks they had, and not useless contrived examples I came up with, it went a lot better. And soon they were quite proficient, and Political Science had its own set of common emacs macros. I got a real understanding of how much 'retype it by hand, it is faster' you do, if your normal rate of typing is 165 wpm or more. Especially if you grew up with paper, not computers, where retyping it was considered very normal ... At any rate when I heard about this experiment I got the secretaries to compete, for fun. The secretaries with their own emacs macros beat the heck out of everybody else at 'copying and moving text around', which was, after all, something they did all of the time. The researchers thought that this wasn't a fair test, as the playing field was so far from level. The secretaries thought they could better their score if they had been given the task the night before -- as they would have designed an even better emacs macro. And, of course, if they had a lot of that particular task to do, they would have 'had Caroline write one and teach it to us', as was usual. Which got people down to the heart of the matter. People wanted to measur
Re: Footnotes in ReST
In a message of Sat, 03 Oct 2015 21:39:26 +1000, "Steven D'Aprano" writes: >I have a document written in Restructured Text format, and I use lots of >footnotes: > >blah blah blah [1]_ and blah blah blah [2]_. >blah blah [3]_ blah ... blah blah >blah blah [999]_. > >.. [1] fe >.. [2] fi >.. [3] fo > ... >.. [999] fum > > >I need to add a footnote between [2] and [3], but I don't want to have to >renumber the following 997 footnotes by hand. Is there something I can do, >within the syntax of ReST itself, to help? > > >-- >Steven You shouldn't have numbered them manually in the first place. Use '#' instead to get automatic numbered footnotes. http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#footnote-references Laura -- https://mail.python.org/mailman/listinfo/python-list
Re: Check if a given value is out of certain range
On Sat, 3 Oct 2015 10:12 pm, Laura Creighton wrote: > People think logically LOL :-) -- Steven -- https://mail.python.org/mailman/listinfo/python-list
Re: Footnotes in ReST
On Sat, 3 Oct 2015 10:21 pm, Laura Creighton wrote: > In a message of Sat, 03 Oct 2015 21:39:26 +1000, "Steven D'Aprano" writes: >>I have a document written in Restructured Text format, and I use lots of >>footnotes: [...] > You shouldn't have numbered them manually in the first place. > Use '#' instead to get automatic numbered footnotes. > http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#footnote-references Thanks. Especially useful is the ability to label footnotes so that they can be auto-numbered while still being able to refer to them from multiple places: If [#note]_ is the first footnote reference, it will show up as "[1]". We can refer to it again as [#note]_ and again see "[1]". We can also refer to it as note_ (an ordinary internal hyperlink reference). .. [#note] This is the footnote labeled "note". That's the problem I was trying to solve by manual numbering. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
Re: Pyserial and Ubuntu Linux kernel 3.13.0-65-generic
On 10/03/2015 03:19 AM, Laura Creighton wrote: > With better searching, I find this bug. > https://bugs.launchpad.net/ubuntu/+source/linux-lts-trusty/+bug/1501345 > > Looks like that's the real one. This ubuntu bug and the other bug you mention seem to be about FTDI devices. Rob said in his original post that the problem occurs with a real UART serial port as well, and also the prolific USB chipset. -- https://mail.python.org/mailman/listinfo/python-list
Re: Newbie: Designer Looking to Build Graphics Editor (PS/AI)
On 10/02/2015 02:23 PM, Kenneth L wrote: > No don't tell me what to do. I joined the military 3 years ago. You > wouldn't believe the stuff I wasn't able to do before but now I am. > You can keep your advice to yourself. I wasn't asking for something > simple. I was asking for a starting point. The 3d was to show you > I've learned hard stuff and it didn't scare me. I was building web > pages when I was in grade school late 90s. I had no idea how to build > an iPhone app but I created one, lol. > > I want to build a graphics program or even a prototype. Maybe I can > pass it over to a expert and hire then to build it. I have a dozen > degree and certificates on my wall. And I didn't get that by going > basic. Keep your advice Bartc. No one is insulting your intelligence, so there's no need to get snippy. It's easy to take offense in an environment like this as things sound much harsher in our own heads than they were likely intended. The reason that you're not getting the responses you want is because what you are asking for involves so many different things it's hard to know how to respond. I have no doubt you may be able to do much of what you want, but it will take a lot of time and a lot of googling of various things. Sounds like you need to search for information concerning: - Python programming in general (tutorials, mini courses, etc) - GUI programming in Python. There are many options here including tkinter, PyQt (or PySide), PyGObject (GTK+ 3.x), and also Kivy. - Vector drawing libraries (PyQt has support, Cairo is another library, maybe a python-based svg library) - bitmap graphics engine of some kind, probably GEGL, which has Python bindings - linear algebra I'm sure you can learn all this, but you aren't going to be able to come here and simply ask about how to put everything together: there's no turn-key solution we can point you to. Fire up your browser and start learning about each of these things. Take heart, though. One man created this all by himself using the C# language: http://www.getpaint.net/index.html Tearing down the GIMP is an excellent idea, though that will also be very daunting. GIMP is a huge program, written in C. On the subject of GIMP, I find it interesting you dismissed it out of hand. GIMP is certainly deficient in many areas, but to say you can't use it because it's so different from Photoshop strikes me as, well, a cop out. Photoshop is intuitive because you learned it. As you are fond of talking about how much you enjoy learning, so learn how to use the GIMP, and as Laura said, hack on it using Python to make add-ons. -- https://mail.python.org/mailman/listinfo/python-list
Re: Pyserial and Ubuntu Linux kernel 3.13.0-65-generic
In a message of Sat, 03 Oct 2015 08:38:53 -0600, Michael Torrie writes: >On 10/03/2015 03:19 AM, Laura Creighton wrote: >> With better searching, I find this bug. >> https://bugs.launchpad.net/ubuntu/+source/linux-lts-trusty/+bug/1501345 >> >> Looks like that's the real one. > >This ubuntu bug and the other bug you mention seem to be about FTDI >devices. Rob said in his original post that the problem occurs with a >real UART serial port as well, and also the prolific USB chipset. > >-- >https://mail.python.org/mailman/listinfo/python-list https://bugs.launchpad.net/ubuntu/+source/linux-lts-trusty/+bug/1501345 seems to be about a whole lot of serial ports to me, not just FTDI Laura -- https://mail.python.org/mailman/listinfo/python-list
function code snippet that has function calls I have never seen before. How does it work.
def funA(x,y,z): return (x+y) * z def funB(x,y): return(x-y) print(funA(4,funB(2,3), funB(3,2))) the answer is 3. I don't know how it works. -- https://mail.python.org/mailman/listinfo/python-list
Re: function code snippet that has function calls I have never seen before. How does it work.
On Sat, Oct 3, 2015 at 1:40 PM, Ronald Cosentino wrote: > def funA(x,y,z): > return (x+y) * z > The above takes 3 values and returns a value > def funB(x,y): > return(x-y) > The above takes 2 values and returns a value > print(funA(4,funB(2,3), funB(3,2))) > you are printing the result of funA, to which you are passing 4, the value returned by funB(2,3) and the value returned by funB(3,2) So, print(funA(4, -1, 1)) Which is 4 + -1 * 1 Which is 3 * 1 > > the answer is 3. I don't know how it works. > > -- > https://mail.python.org/mailman/listinfo/python-list > -- Joel Goldstick http://joelgoldstick.com -- https://mail.python.org/mailman/listinfo/python-list
RE: function code snippet that has function calls I have never seen before. How does it work.
Hi Ronald, Answers inline. -Original Message- From: Python-list [mailto:python-list-bounces+joseph.lee22590=gmail@python.org] On Behalf Of Ronald Cosentino Sent: Saturday, October 3, 2015 10:41 AM To: python-list@python.org Subject: function code snippet that has function calls I have never seen before. How does it work. def funA(x,y,z): return (x+y) * z def funB(x,y): return(x-y) print(funA(4,funB(2,3), funB(3,2))) the answer is 3. I don't know how it works. JL: Okay, let's step through the print routine. 1. Before print does its job, the function result will be gathered. 2. The argument to print is result of funA, which itself takes result of two calls to FunB. 3. First, results of funB calls will be gathered (subtracting 3 from 2 and 2 from 3, respectively). So it becomes: print(funA(4, (2-3), (3-2))) 4. Then funA will continue to perform its job, returning the result for output. Thus the final expression that print will print is: print((4+-1) * 1) When looking at a function that takes result of another function, it is important to look at what the inner callee does (in this case, look at what funB does first). Cheers, Joseph -- https://mail.python.org/mailman/listinfo/python-list -- https://mail.python.org/mailman/listinfo/python-list
Re: function code snippet that has function calls I have never seen before. How does it work.
hi, On Sat, Oct 03, 2015 at 10:40:57AM -0700, Ronald Cosentino wrote: > def funA(x,y,z): > return (x+y) * z > def funB(x,y): > return(x-y) > print(funA(4,funB(2,3), funB(3,2))) > > the answer is 3. I don't know how it works. it's simple: - there is a "composition of functions", generally f(g()) (function in argument list of another function) - first, Python evaulates the arguments first, from left to right - in this point, you'll get -1 for 2nd arg, and 1 for 3rd arg - then your funcA() will be called with these arguents: 4, -1, 1 - funcA() calculates this: (x+y)*z, in this case (4+(-1))*1 which is 3... a. -- I � UTF-8 -- https://mail.python.org/mailman/listinfo/python-list
Re: function code snippet that has function calls I have never seen before. How does it work.
On Sat, 03 Oct 2015 10:40:57 -0700, Ronald Cosentino wrote: > def funA(x,y,z): > return (x+y) * z > def funB(x,y): > return(x-y) > print(funA(4,funB(2,3), funB(3,2))) > > the answer is 3. I don't know how it works. def funA(x, y, z): return (x+y) * z def funB(x, y): return (x-y) # this line # print(funA(4,funB(2,3), funB(3,2))) # can be written as the following 4 lines: a = funB(2, 3) # 2 - 3 -> -1 b = funB(3, 2) # 3 - 2 -> 1 c = funA(4, a, b) # (4 + -1) * 1 -> 3 print(c) # 3 -- Denis McMahon, denismfmcma...@gmail.com -- https://mail.python.org/mailman/listinfo/python-list
