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  • When/Why ( if ever ) should i think about doing Generic Programming/Meta Programming

    - by hotadvice
    Hi there IMHO to me OOPS, design patterns make sense and i have been able to apply them practically. But when it comes to "generic programming /meta programming" of the Modern C++ kind, i am left confused. -- Is it a new programming/design paradigm ? -- Is it just limited to "library development"? If not, What design/coding situations call for using meta programming/generic programming. -- Does using templates mean i am doing generic programming? I have googled a lot on this topic but do not grasp the BIG PICTURE fully. Also see this post. After reading dicussions here under, up till now, I am sure ( might still not be correct): a) Generic programming and meta programming are two different concepts.

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  • Using Python to get a CSV output for the following example.

    - by Az
    Hi there, I'm back again with my ongoing saga of Student-Project Allocation questions. Thanks to Moron (who does not match his namesake) I've got a bit of direction for an evaluation portion of my project. Going with the idea of the Assignment Problem and Hungarian Algorithm I would like to express my data in the form of a .csv file which would end up looking like this in spreadsheet form. This is based on the structure I saw here. | | Project 1 | Project 2 | Project 3 | |----------|-----------|-----------|-----------| |Student1 | | 2 | 1 | |----------|-----------|-----------|-----------| |Student2 | 1 | 2 | 3 | |----------|-----------|-----------|-----------| |Student3 | 1 | 3 | 2 | |----------|-----------|-----------|-----------| To make it less cryptic: the rows are the Students/Agents and the columns represent Projects/Task. Obviously ONE project can be assigned to ONE student. That, in short, is what my project is about. The fields represent the preference weights the students have placed upon the projects (ranging from 1 to 10). If blank, that student does not want that project and there's no chance of him/her being assigned such. Anyway, my data is stored within dictionaries. Specifically the students and projects dictionaries such that: students[student_id] = Student(student_id, student_name, alloc_proj, alloc_proj_rank, preferences) where preferences is in the form of a dictionary such that preferences[rank] = {project_id} and projects[project_id] = Project(project_id, project_name) I'm aware that sorted(students.keys()) will give me a sorted list of all the student IDs which will populate the row labels and sorted(projects.keys()) will give me the list I need to populate the column labels. Thus for each student, I'd go into their preferences dictionary and match the applicable projects to ranks. I can do that much. Where I'm failing is understanding how to create a .csv file. Any help, pointers or good tutorials will be highly appreciated.

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  • What is the worst class/variable/function name you have ever encountered

    - by Chris Noe
    Naming things well is arguably Job 1 for professional programmers. Yet we have all suffered from some bad naming choices from time to time. So just to vent a little, what are some doozies that you may have run across? Just to get things started: One of our original developers wasn't sure what to call a secondary key - on what turned out to be a primary table for this app - so he called it: DL2WhateverTheHellThatIs. Unfortunately this system generates entity mappings from the XML, and attributes defined there result in classes, methods, and constants that are referenced through-out the app. To this day it is very hard to find a source file that does not reference this, er, thing! A few actual examples: DL2WhateverTheHellThatIsBean cos = (DL2WhateverTheHellThatIsBean)itr.next(); String code = getDL2WhateverTheHellThatIs().getCode(); From from = new From("DL2WhateverTheHellThatIs"); String filter = "_dL2WhateverTheHellThatIs._code"; (Very difficult to refactor)

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  • Python - How to find a correlation between two vectors ?

    - by psihodelia
    Given two vectors X and Y I have to find their correlation, i.e. their linear dependence/independence. Both vectors have equal dimension. A resulted answer should be a floating point number from [-1.0 .. 1.0]. Example: X=[-1, 2, 0] Y=[ 4, 2, -0.3] Find y=cor(X,Y) such that y belongs to [-1.0 .. 1.0]. It should be a simple construction involving a list-comprehension. No external library is allowed. UPDATE: ok, if dot product is enough, then here is my solution: nX = 1/(sum([x*x for x in X]) ** 0.5) nY = 1/(sum([y*y for y in Y]) ** 0.5) cor = sum([(x*nX)*(y*nY) for x,y in zip(X,Y) ]) right?

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  • How should I write this string-prefix check so that it's idiomatic Python?

    - by Kevin Stargel
    I have a couple of lists of items: specials = ['apple', 'banana', 'cherry', ...] smoothies = ['banana-apple', 'mocha mango', ...] I want to make a new list, special_smoothies, consisting of elements in smoothies that start with the elements in specials. However, if specials is blank, special_smoothies should be identical to smoothies. What's the most Pythonic way to do this? Is there a way to do this without a separate conditional check on whether specials is blank?

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  • How does one pre-populate a Python Formish form?

    - by Jace
    How does one pre-populate a Formish form? The obvious method as per the documentation doesn't seem right. Using one of the provided examples: import formish, schemaish structure = schemaish.Structure() structure.add( 'a', schemaish.String() ) structure.add( 'b', schemaish.Integer() ) schema = schemaish.Structure() schema.add( 'myStruct', structure ) form = formish.Form(schema, 'form') If we pass this a valid request object: form.validate(request) The output is a structure like this: {'myStruct': {'a': 'value', 'b': 0 }} However, pre-populating the form using defaults requires this: form.defaults = {'myStruct.a': 'value', 'myStruct.b': 0} The dottedish package has a DottedDict object that can convert a nested dict to a dotted dict, but this asymmetry doesn't seem right. Is there a better way to do this?

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  • Calculating probability that a string has been randomized? - Python

    - by RadiantHex
    Hi folks, this is correlated to a question I asked earlier (question) I have a list of manually created strings such as: lucy87 gordan_king fancy_unicorn77 joplucky_kanga90 base_belong_to_narwhals and a list of randomized strings: johnkdf pancake90kgjd fancy_jagookfk manhattanljg What gives away that the last set of strings are randomized is that sequences such as 'kjg', 'jgf', 'lkd', ... . Any clever way I could separate strings that contain these apparently randomized strings from the crowd? I guess that this plays a lot on the fact that certain characters are more likely to be placed next to others (e.g. 'co', 'ka', 'ja', ...). Any ideas on this one? Kylotan mentioned Reverend, but I am not sure if it can be used fr such purpose. Help would be much appreciated!

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  • How to create a complete binary tree of height 'h' using Python?

    - by Jack
    Here is the node structure class Node: def __init__(self, data): # initializes the data members self.left = None self.right = None self.parent = None self.data = data complete binary tree Definition: A binary tree in which every level, except possibly the deepest, is completely filled. At depth n, the height of the tree, all nodes must be as far left as possible. -- http://www.itl.nist.gov/div897/sqg/dads/HTML/completeBinaryTree.html I am looking for an efficient algorithm.

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  • Can you authenticate Facebook Graph entirely from command line with Python?

    - by Sebastian
    I'm writing a (tabbed) application for Facebook that requires a background process to run on a server and, periodically, upload images to an album on this application's page. What I'm trying to do is create a script that will: a) authenticate me with the program b) upload an image to a specific album All of this entirely from the command line and completely with the new Graph API. My problem right now is trying to locate the documentation that will allow me to get a token without a pop-up window of sorts. Thoughts?

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  • [Python] How can I speed up unpickling large objects if I have plenty of RAM?

    - by conradlee
    It's taking me up to an hour to read a 1-gigabyte NetworkX graph data structure using cPickle (its 1-GB when stored on disk as a binary pickle file). Note that the file quickly loads into memory. In other words, if I run: import cPickle as pickle f = open("bigNetworkXGraph.pickle","rb") binary_data = f.read() # This part doesn't take long graph = pickle.loads(binary_data) # This takes ages How can I speed this last operation up? Note that I have tried pickling the data both in using both binary protocols (1 and 2), and it doesn't seem to make much difference which protocol I use. Also note that although I am using the "loads" (meaning "load string") function above, it is loading binary data, not ascii-data. I have 128gb of RAM on the system I'm using, so I'm hoping that somebody will tell me how to increase some read buffer buried in the pickle implementation.

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  • Is it possible to craft your own packets with python?

    - by Rob
    Well, I know its possible, using external libraries and modules such as scapy. But how about without external modules? Without running the script as root? No external dependencies? I've been doing a lot of googling, but haven't found much help. I'd like to be able to create my own packets, but without running as root, or installing extra dependencies. Any suggestions?

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  • Python Pickle: what can cause stack index out of range error?

    - by Rosarch
    I'm getting this error: File "C:\Python26\lib\pickle.py", line 1374, in loads return Unpickler(file).load() File "C:\Python26\lib\pickle.py", line 858, in load dispatch[key](self) File "C:\Python26\lib\pickle.py", line 1075, in load_obj k = self.marker() File "C:\Python26\lib\pickle.py", line 874, in marker while stack[k] is not mark: k = k-1 IndexError: list index out of range Why could this be happening?

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  • How do I modify this download function in Python?

    - by TIMEX
    Right now, it's iffy. Gzip, images, sometimes it doesn't work. How do I modify this download function so that it can work with anything? (Regardless of gzip or any header?) How do I automatically "Detect" if it's gzip? I don't want to always pass True/False, like I do right now. def download(source_url, g = False, correct_url = True): try: socket.setdefaulttimeout(10) agents = ['Mozilla/4.0 (compatible; MSIE 5.5; Windows NT 5.0)','Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 5.1)','Microsoft Internet Explorer/4.0b1 (Windows 95)','Opera/8.00 (Windows NT 5.1; U; en)'] ree = urllib2.Request(source_url) ree.add_header('User-Agent',random.choice(agents)) ree.add_header('Accept-encoding', 'gzip') opener = urllib2.build_opener() h = opener.open(ree).read() if g: compressedstream = StringIO(h) gzipper = gzip.GzipFile(fileobj=compressedstream) data = gzipper.read() return data else: return h except Exception, e: return ""

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  • How do I add a method with a decorator to a class in python?

    - by Timmy
    How do I add a method with a decorator to a class? I tried def add_decorator( cls ): @dec def update(self): pass cls.update = update usage add_decorator( MyClass ) MyClass.update() but MyClass.update does not have the decorator @dec did not apply to update I'm trying to use this with orm.reconstructor in sqlalchemy.

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  • how to set a fixed color bar for pcolor in python matplotlib?

    - by user248237
    I am using pcolor with a custom color map to plot a matrix of values. I set my color map so that low values are white and high values are red, as shown below. All of my matrices have values between 0 and 20 (inclusive) and I'd like 20 to always be pure red and 0 to always be pure white, even if the matrix has values that don't span the entire range. For example, if my matrix only has values between 2 and 7, I don't want it to plot 2 as white and 7 as red, but rather color it as if the range is still 0 to 20. How can I do this? I tried using the "ticks=" option of colorbar but it did not work. Here is my current code (assume "my_matrix" contains the values to be plotted): cdict = {'red': ((0.0, 1.0, 1.0), (0.5, 1.0, 1.0), (1.0, 1.0, 1.0)), 'green': ((0.0, 1.0, 1.0), (0.5, 1.0, 1.0), (1.0, 0.0, 0.0)), 'blue': ((0.0, 1.0, 1.0), (0.5, 1.0, 1.0), (1.0, 0.0, 0.0))} my_cmap = matplotlib.colors.LinearSegmentedColormap('my_colormap', cdict, 256) colored_matrix = plt.pcolor(my_matrix, cmap=my_cmap) plt.colorbar(colored_matrix, ticks=[0, 5, 10, 15, 20]) any idea how I can fix this to get the right result? thanks very much.

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  • Is it possible to create a python iterator over pre-defined mutable data?

    - by Wilduck
    I might be doing this wrong, if I am, let me know, but I'm curious if the following is possible: I have a class that holds a number of dictionaries, each of which pairs names to a different set of objects of a given class. For example: items = {"ball" : ItemInstance1, "sword" : ItemInstance2} people = {"Jerry" : PersonInstance1, "Bob" : PersonInstance2, "Jill" : PersonInstance3} My class would then hold the current items and people that are availible, and these would be subject to change as the state changes: Class State: def __init__(self, items, people): self.items = items self.people = people I would like to define a iter() and next() method such that it iterates through all of the values in its attributes. My first question is whether or not this is possible. If it is, will it be able to support a situation as follows: I define items and people as above then: state = State(items, people) for names, thing in state: print name + " is " + thing.color items[cheese] = ItemInstance3 for names, thing in state: print name + " weighs " + thing.weight While I feel like this would be usefull in the code I have, I don't know if it's either possible or the right approach. Everything I've read about user defined iterators has suggested that each instance of them is one use only.

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