🌐 Mailman 3 December 2014 - Python-list - python.org

Re: Language design
by Steven D'Aprano June 2, 2015

June 2, 2015

On Wed, 11 Sep 2013 14:30:54 -0700, Mark Janssen wrote: > 1) It tried to make Object the parent of every class. Tried, and succeeded. > No one's close enough to God to make that work. Non-sequitor. One doesn't need to be close to a deity to have a single root of the object hierarchy. > 2) It didn't make dicts inherit from sets when they were added to > Python. Why would you want dicts to inherit from sets? > 3) It used the set literal for dict, so that there's no obvious > way to do it. This didn't get changed in Py3k. No, it uses the dict literal for dicts. And the obvious way to form an empty set is by calling set(), the same as str(), int(), list(), float(), tuple(), dict(), ... > 4?) It allowed > [reference] variables to be used as dict keys. This creates a parsing > difficulty for me, mentally. Keys should be direct, hashable values, > not hidden in a variable name. I don't even understand what you are talking about here. "[reference] variables"? What does that mean? Dict keys are direct, hashable values, and I have no idea what you mean by "hidden in a variable name". -- Steven

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Re: Message passing syntax for objects | OOPv2
by Steven D'Aprano June 2, 2015

June 2, 2015

On Wed, 08 May 2013 19:35:58 -0700, Mark Janssen wrote: > Long story short: the lambda > calculus folks have to split from the Turing machine folks. > These models of computation should not use the same language. Their > computation models are too radically different. Their computation models are exactly equivalent. This is like saying that Cartesian coordinates and polar coordinates are so radically different that they cannot possibly both describe the same space. -- Steven

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FYI: Micro Python running on kickstarter pyBoard project, now shipping
by jkn May 27, 2015

May 27, 2015

Hi all I haven't heard in mentioned here, but since I saw one of the boards today thought I'd pass on the news: The Kickstarter 'MicroPython' project, which has a tiny 'pyboard' (only a couple of sq.inches in size) with a processor running 'a complete re-write of the Python (version 3.4) programming language so that it fits and runs on a microcontroller' is now shipping. https://micropython.org/ Looks nice; I have no connection but will be getting one myself to play with... Cheers J^n

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Array of Functions
by Richard Riehle May 27, 2015

May 27, 2015

In C, C++, Ada, and functional languages, I can create an array of functions, albeit with the nastiness of pointers in the C family. For example, an array of functions where each function is an active button, or an array of functions that behave like formulae in a spreadsheet. I am finding this a bit challenging in Python. Example: r1c1 r1c2 r1c3 r2c1 r2c2 r2c3 r3c1 r3c2 r3c3 where r1 is row 1 and c1 is column 1. Suppose I want an array where the colum three is a set of functions that operates on the other two columns, depending on the values I set for those rows and columns? As noted, I can do this pretty easily in most languages (well, except for Java which does not support any kind of functional programming capability), even if I have to use pointers. I think my difficulty is related to the REPL nature of Python. However, I am sure some clever Pythonista has found a way to do this. Thanks in advance for any suggestions, Richard Riehle, PhD, International Technological University, San Jose, CA

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My attempts in playing with tail-recursion in python
by Thomas Baruchel May 17, 2015

May 17, 2015

Hi, I would like to share some of my recent attempts concerning recursivity in python, more precisely recursivity with lambda functions. I know that the title of my thread with the "tail-recursion" words may wake up some long and old war; please don't take it as such. I am not claiming anything about what programming languages should be or not; I enjoy using python for many purposes and I perfectly know how to handle loops for achieving some tasks, but sometimes I like rather think with recursivity because I have been using various dialects of Lisp for a long time. I had a very great time studying the Y-combinator; then I wrote various pieces of code for remapping recursive calls to loop iterations. The following functions are fully usable; I hope someone will enjoy using them. If you are not interested by the explanations, just jump to the end of the message and take my functions for using them. Here is a recursive function: fac = lambda f: lambda n: 1 if n==0 else n*f(n-1) The Y-combinator is well known: Y = lambda f: (lambda x: x(x))(lambda y: f(lambda *args: y(y)(*args))) Now, you can use the recursive function: rf = Y(fac) rf(5) Now we write fac as a tail-recursive function: fac = lambda f: lambda a,b: b if a==0 else f(a-1,a*b) rf = Y(fac) rf(5,1) but of course, the recursivity is handled like previously. In fact, it is very easy to build some effcient wrapper; for instance: (lambda f: f(lambda *args: ("callback",args))) will act in the following way: (lambda f: f(lambda *args: ("callback",args)))(fac)(5,1) --> ('callback', (4, 5)) (lambda f: f(lambda *args: ("callback",args)))(fac)(4,5) --> ('callback', (3, 20)) (lambda f: f(lambda *args: ("callback",args)))(fac)(3,20)) --> ('callback', (2, 60)) (lambda f: f(lambda *args: ("callback",args)))(fac)(2,60) --> ('callback', (1, 120)) (lambda f: f(lambda *args: ("callback",args)))(fac)(1,120) --> ('callback', (0, 120)) (lambda f: f(lambda *args: ("callback",args)))(fac)(0,120) --> 120 Here, the "callback" string is arbitrary chosen in order to make the loop know that a next call is needed. Now, the recursivity is handled as successive calls, which is what I was looking for. A first proposal could be: def with_tail_recursion(func): x = (lambda f: f(lambda *args: ("callback",args)))(func) def wrapper(*args): out = ("callback",args) while type(out)==tuple and out[0]=="callback": out = x(*out[1]) return out return wrapper Now, the very same function can be used as recursive or inside a loop: fac = lambda f: lambda a,b: b if a==0 else f(a-1,a*b) rf = Y(fac) tr = with_tail_recursion(fac) rf(5,1) --> 120 tr(5,1) --> 120 Of course, if most of your job relies on writing functions returning tuples with the string "callback" being the first argument, you should use another keyword in the previous code ;-) You can inspect the stack by raising an exception: f2 = lambda f: lambda n: 1/n if n==0 else f(n-1) and see the differences between Y(f2)(5) and with_tail_recursion(f2)(5) But I was not fully happy with the use of a tuple, efficient but a little too tricky to my eyes. For that reason, I took the Y combinator again and slightly modified it: lambda f: (lambda x: x(x))(lambda y: f(lambda *args: lambda: y(y)(*args))) Now, the function doesn't call itself, but returns a function calling itself with the relevant arguments. I like this new function better than the previous one, but it is now more difficult for the wrapper to detect when it is time to leave the loop. Right now, I use the following test: checking for the __call__ string in the dir() list. This means ONE IMPORTANT THING: this second wrapper can't handle tail-recursive functions returning functions, (which is actually more likely to happen than tail-recursive functions returning tuples with the string "callback" being the first argument ;-) ). But I like it that way: def B(func): x = (lambda f: (lambda x: x(x))(lambda y: f(lambda *args: lambda: y(y)(*args))))(func) def wrapper(*args): out = x(*args) while '__call__' in dir(out): out = out() return out return wrapper tr2 = B(fac) tr2(5,1) --> 120 Now, you can write functions with a huge depth of recusivity with no problem : B(lambda f: lambda n: "ok" if n==0 else f(n-1))(5000) (don't try with the Y combinator instead...) Best regards, -- Thomas Baruchel

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Confessions of a Python fanboy
by r May 11, 2015

May 11, 2015

Hello fellow Pythonista's it's nice to be back after such a long hiatus. I have recently realized my blind love affair with Python was just that. I must admit there are better ways to program. Like your first lay, your first programing language can leave an indelible mark on you, but like all young chaps, the passion for programming has sweep me away into vast new orgies of programming bliss. (ig ,little head guides the big one.) My adventures in Ruby. an autobyography by rt8396 After breaking free from the wild love affair i had with Python, a new day had dawned. I dried my eyes and soon discovered the Ruby language (not by choice however) --now don't worry fellow Pythonistas, i am still on your side (mostly) -- but i now realize Ruby has some good things going for it. For instance... 1.) No need to use "()" to call a function with no arguments. Python --> "obj.m2().m3()" --ugly Ruby --> "obj.m1.m2.m3" -- sweeet! Man, i must admit i really like this, and your code will look so much cleaner. 2.) the .each method container.each{|localVar| block} This method can really cleanup some ugly for loops, although i really like the readability of for loops. 3.) true OOP Now before you go and get all "huffy" over this statement, hear me out. Python is the best language in the world. But it damn sure has some warts! "len(this)" instead of "obj.length" max(that) instead of [1,2,3,4,5].max(). You know what i am talking about here people. We all get complacent and It seems easier to just cope with these problems instead of fighting for change. But look at the French, WHAT THE HELL HAS THAT DONE FOR THEM, *NOTHING*!!!! As for the rest of Ruby, i am not impressed. The redundant usage of "end" over indention perplexes me. The Perlish feel of "require" and the horrifically cryptic idioms of Ruby regular expressions. The "puts" and "gets" seem childish and the math class does not even have a degrees or radians function! Anyway, i thought i would get this off my chest and catch up with old friends in the meantime. We can all make Python the perfect language it needs to be, but it ain't gonna be easy! Thank you all PS stay tuned for more from this series....

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Custom alphabetical sort
by Pander Musubi May 2, 2015

May 2, 2015

Hi all, I would like to sort according to this order: (' ', '.', '\'', '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'A', 'ä', 'Ä', 'á', 'Á', 'â', 'Â', 'à', 'À', 'å', 'Å', 'b', 'B', 'c', 'C', 'ç', 'Ç', 'd', 'D', 'e', 'E', 'ë', 'Ë', 'é', 'É', 'ê', 'Ê', 'è', 'È', 'f', 'F', 'g', 'G', 'h', 'H', 'i', 'I', 'ï', 'Ï', 'í', 'Í', 'î', 'Î', 'ì', 'Ì', 'j', 'J', 'k', 'K', 'l', 'L', 'm', 'M', 'n', 'ñ', 'N', 'Ñ', 'o', 'O', 'ö', 'Ö', 'ó', 'Ó', 'ô', 'Ô', 'ò', 'Ò', 'ø', 'Ø', 'p', 'P', 'q', 'Q', 'r', 'R', 's', 'S', 't', 'T', 'u', 'U', 'ü', 'Ü', 'ú', 'Ú', 'û', 'Û', 'ù', 'Ù', 'v', 'V', 'w', 'W', 'x', 'X', 'y', 'Y', 'z', 'Z') How can I do this? The default sorted() does not give the desired result. Thanks, Pander

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How to receive a data file of unknown length using a python socket?
by twgray April 22, 2015

April 22, 2015

I am attempting to send a jpeg image file created on an embedded device over a wifi socket to a Python client running on a Linux pc (Ubuntu). All works well, except I don't know, on the pc client side, what the file size is? The following is a snippet: [code] f = open("frame.jpg",mode = 'wb') while True: data = self.s.recv(MAXPACKETLEN) if len(data) == 0: break recvd += len(data) f.write(data) f.close() [end] It appears to be locking up in 'data=self.s.recv(MAXPACKETLEN)' on the final packet, which will always be less than MAXPACKETLEN. I guess my question is, how do I detect end of data on the client side?

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Python newbie here! No module named settings
by Neeraj Agarwal April 13, 2015

April 13, 2015

Hello all, I'm a newbie to Python and its my 2nd day exploring it. I was trying to use Python wrapper for Google Charts API and was tweaking the examples. https://github.com/gak/pygooglechart/raw/master/examples/pie.py This is the script which I was trying. And the python interpreter gives the following error: import settings ImportError: No module named settings I installed Django as well before this (if its causing the problem, dunno) Please help me. Thanks, Neeraj

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Python to C++ in a pickle
by Larry Whitley April 2, 2015

April 2, 2015

I'd like to pickle an object in python and unpickle it in C++. The object in question is a python dictionary so it will have to go into a C++ map. Has someone done this and is willing to share? Or, is the cPickle source available on the web somewhere? Larry

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