Re: How can I verify if the content of a variable is a list or a string?
You can do it more concise. def isListOrString(p): ...return any((isinstance(p,list),isinstance(p,str))) ... listOrString(string) True listOrString([1,2,3]) True listOrString(2) False listOrString(False) False Rainer -- http://mail.python.org/mailman/listinfo/python-list
Re: Scope of variable inside list comprehensions?
Hello, try: songs = [Song(id) for id in song_ids] except Song.DoesNotExist: print unknown song id (%d) % id that's is a bad programming style. So it will be forbidden with python 3. The reason is that list comprehension is a construct from the functional world. It's only syntactic sugar for the functions map and filter. So functions have to be pure functions. To say it in other words, they have to be side-effect free. But the python construct from above pollutes the namespace with name id. Greetings from Rottenburg, Rainer -- http://mail.python.org/mailman/listinfo/python-list
Aw: Functional style programming in python: what will you talk about if you have an hour on this topic?
Hello, (My post did not appear in the mailing list, so this is my second try. Apology if it ends up posted twice) Hi, all, If you have read my previous posts to the group, you probably have some idea why I asked this question. I am giving a few presentations on python to my colleagues who are mainly java developers and starting to pick up python at work. I think it's relatively difficult to get a feeling what a are the key points behind functional programming. So I think you should start explaining the concepts behind functional programming. A few ideas. - higher order functions - first class functions - currying - pure functions - list processing - lambda functions - recursion instead of iteration - pattern matching And that should end with the three guys (map, filter and reduce ) as building blocks of functional programming. And that is a good point to introduce list comprehension. Because it's only syntactic sugar for map filter. But what kind of sugar. It's very impressive. Thats my typical way to introduce it in seminars. Now it's a good time to explain, what's special in python with functional programming. (A lot if you compare it with haskell) I wrote an article about your topic. You have only to learn german. About the concepts: http://www.linux-magazin.de/Online-Artikel/Funktionale-Programmierung-1-Grundzuege?category=0 What's special about Python: http://www.linux-magazin.de/NEWS/Online-Artikel-Funktionale-Programmierung-in-Python?category=0 Greetings from Rottenburg, Rainer -- http://mail.python.org/mailman/listinfo/python-list
Aw: Re: Aw: Functional style programming in python: what will you talk about if you have an hour on this topic?
Am Samstag, 16. Juli 2011 08:46:42 UTC+2 schrieb Steven D#39;Aprano: Rainer Grimm wrote: I think it's relatively difficult to get a feeling what a are the key points behind functional programming. So I think you should start explaining the concepts behind functional programming. A few ideas. - higher order functions - first class functions - currying - pure functions - list processing - lambda functions - recursion instead of iteration - pattern matching Avoiding global state. Thats pure functions. Lazy data processing, including infinite data streams. You are right. I forget to mention lazy versus eager evaluation. Decorators. Iterators. Using iterators as a form of pipelining. Thats special about python adapting functional ideas. Some of these might not count as strictly functional in the lambda calculus sense, but they're closely related and less academic and more practical. And that should end with the three guys (map, filter and reduce ) as building blocks of functional programming. And that is a good point to introduce list comprehension. Because it's only syntactic sugar for map filter. But what kind of sugar. It's very impressive. Thats my typical way to introduce it in seminars. If it were me, I'd probably take a less pure approach and concentrate on concrete examples. As far as Python goes, the use of list comps/generator expressions, iterators and decorators are the main functional idioms, not so much map, filter and especially reduce, which only avoided being removed from Python 3 by the narrowest margin. That is not my point. Before you talk about functional, your audience have to have a feeling, what you are talking about. The problem with functional is, that this expression is very difficult to grab. Like 15 years ago with OO or Design Pattern 10 years ago. I think the ideas behind functional programming are so great, that they a worth to reason a little bit about. Especially for people, that think, each problem can be solved in a OO manner. But to be honest. I gave a many python seminars in the last years, talking 3 hours about functional programming in Python and use no pure approach. Sorry I answered to fast in my first mail. He asked for functional style programming, not functional programming in Python and doing the whole in one hour. Maybe the hour is a good starting point for further investigations. Greeting from Rottenburg, Rainer -- http://mail.python.org/mailman/listinfo/python-list
Re: What is a list compression in Python?
Hallo, you can also look at list comprehension as syntactic sugar for the functions map and filter. The two functions from the functional world can be expressed in a comprehensive way with list comprehension. [x**2 for x in range(10) ] == map ( lambda x: x*x, range(10)) True [ x for x in range(10) if x%2 == 0 ] == filter ( lambda x: x%2 == 0 , range(10)) True Greetings -- http://mail.python.org/mailman/listinfo/python-list
Re: multivariable assignment
On Dec 31 2009, 5:13 pm, davidj411 davidj...@gmail.com wrote:
I am not sure why this behavior is this way.
at beginning of script, i want to create a bunch of empty lists and
use each one for its own purpose.
however, updating one list seems to update the others.
a = b = c = []
a.append('1')
a.append('1')
a.append('1')
c
['1', '1', '1']
a
['1', '1', '1']
b
['1', '1', '1']
a, b and c are the same objects.
You can check the object identity by
a = b = c = []
print id(a),id(b),id(c)
3083044140 3083044140 3083044140
a is b is c
True
Greetings
--
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Re: How do I begin debugging a python memory leak?
On 17 Sep., 02:10, Matthew Wilson m...@tplus1.com wrote: I have a web app based on TurboGears 1.0. In the last few days, as traffic and usage has picked up, I noticed that the app went from using 4% of my total memory all the way up to 50%. I suspect I'm loading data from the database and somehow preventing garbage collection. Are there any tools that might help me out with this? If have one of the following plattforms X86/Linux, AMD64/Linux, PPC32/Linux, PPC64/Linux and X86/Darwin (Mac OS X), have a look at valgrind. http://valgrind.org/ I used of often for searching the memory leaks in c++. It's a great tool to analyse your memory behaviour. Greetings -- http://mail.python.org/mailman/listinfo/python-list
Re: How do I begin debugging a python memory leak?
On Sep 18, 5:42 pm, Paul Rubin http://phr...@nospam.invalid wrote: Rainer Grimm r.gr...@science-computing.de writes: have a look at valgrind. Have you actually used that on Python? Not with python as far I can remember. But often with C++ executables, as i mentioned it. I you look at http://valgrind.org/info/ there stands: Valgrind has been used on programs written partly or entirely in C, C+ +, Java, Perl, Python, assembly code, Fortran, Ada, and many others. It exists also a extension for python http://blogs.gnome.org/jamesh/2008/03/24/python-valgrind/ , to get rid of the false positiv errors. So it should be worth a try. -- http://mail.python.org/mailman/listinfo/python-list
Re: invoke method on many instances
Hallo Alan, def apply2(itr, methodname, *args, **kwargs): f = operator.methodcaller(methodname, *args, **kwargs) for item in itr: f(item) you can do it in a functional way. class A(object): ... def hello(self): return hello: + str ( self.__class__.__name__ ) ... class B(A):pass ... class C(A):pass ... a=A() b=B() c=C() a.hello() 'hello: A' b.hello() 'hello: B' c.hello() 'hello: C' map( (lambda obj : getattr(obj,hello)()),(a,b,c)) ['hello: A', 'hello: B', 'hello: C'] [ getattr(obj,hello)() for obj in (a,b,c)] ['hello: A', 'hello: B', 'hello: C'] Greetings from Rottenburg, Rainer -- http://mail.python.org/mailman/listinfo/python-list
Re: Beginner question: module organisation
[EMAIL PROTECTED] wrote: Hello :) I am new to python and I don't have much expirience in object-oriented technologies neither. The problem is the following: I have to create a simple python template script that will always follow the same algorithm, let's say: - read a mesh - transform the mesh (let's say, refine) The last step should be a kind of a black box: - the same input data format - some algorithme inside - the same output data format A number of different refine methods should be implemented. The end- user must be able to write easily a new method and call it from the base script without any major change. Something like this would be a solution (no classes created, no OO programming): - a module defining REFINE1(mesh), REFINE2(mesh), ... - in the script: from MODULE import REFINE2 as REFINE REFINE(mesh) Is it a proper solution for this kind of problem? How would you implement this kind of task? Hello. Have a look at the classical GangOfFour design pattern book. You can especially with the template methode design the processing of your data. The strategy pattern will help you to vary the algroithm in your processing. To be concret, in your base class you define the processing of the data. There are two distinct methods to do it. delegate the variation of the algorithmns to other objects = strategy pattern override the steps of the processing in subclasses = template method Regards, Rainer -- _creating IT solutions Rainer Grimm scVENUS Schulungsleiter science + computing ag phone +49(0)7071 9457-253 Hagellocher Weg 73 fax +49(0)7071 9457-511 D-72070 Tuebingen, Germany [EMAIL PROTECTED]www.science-computing.de -- http://mail.python.org/mailman/listinfo/python-list
Re: a better solution for GUI in python
ce wrote: Hi, My company is using python currently for our website. We need to develop a GUI front-end for our ERP that would be portable (Windows and Linux). My question is which solution would be better for the GUI (and easier to implement)? I knew there are something like wxidgets, QT and pyGTK? actually we will need some complicated stuff in the GUI and yet I don't know much about GUI programming. Any recommendation guys? Hallo. Hava a look at http://www.awaretek.com/toolkits.html . Regards, Rainer -- http://mail.python.org/mailman/listinfo/python-list
