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• What is a django QuerySet?

  - by gath

  Guys, When i do this >>> b = Blog.objects.all() >>> b i get this >>>[<Blog: Blog Title>,<Blog: Blog Tile>] When i query what type b is, >>> type(b) i get this >>> <class 'django.db.models.query.QuerySet'> What does this mean? is it a data type like dict, list etc? An example of how i can build data structure like a QuerySet will be appreciated. I would want to know how django build that QuerySet (the gory details) Gath.

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• python - from matrix to dictionary in single line

  - by Sanich

  matrix is a list of lists. I've to return a dictionary of the form {i:(l1[i],l2[i],...,lm[i])} Where the key i is matched with a tuple the i'th elements from each list. Say matrix=[[1,2,3,4],[9,8,7,6],[4,8,2,6]] so the line: >>> dict([(i,tuple(matrix[k][i] for k in xrange(len(matrix)))) for i in xrange(len(matrix[0]))]) does the job pretty well and outputs: {0: (1, 9, 4), 1: (2, 8, 8), 2: (3, 7, 2), 3: (4, 6, 6)} but fails if the matrix is empty: matrix=[]. The output should be: {} How can i deal with this?

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• Python | How to create dynamic and expandable dictionaries

  - by MMRUser

  I want to create a Python dictionary which holds values in a multidimensional accept and it should be able to expand, this is the structure that the values should be stored :- userdata = {'data':[{'username':'Ronny Leech','age':'22','country':'Siberia'},{'username':'Cronulla James','age':'34','country':'USA'}]} Lets say I want to add another user def user_list(): users = [] for i in xrange(5, 0, -1): lonlatuser.append(('username','%s %s' % firstn, lastn)) lonlatuser.append(('age',age)) lonlatuser.append(('country',country)) return dict(user) This will only returns a dictionary with a single value in it (since the key names are same values will overwritten).So how do I append a set of values to this dictionary. Note: assume age, firstn, lastn and country are dynamically generated. Thanks.

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• C# ToDictionary can valueSelector give null?

  - by Trimack

  Hi, I want to make a dictionary out of list in a way, that the list becomes keys and values would be empty. I have following code Dictionary<XmlTest, int?> testBattery = new XmlTests().GetRandomTestBattery(id). ToDictionary(k => k, v => null); But I am getting the error "Cannot convert lambda expression to type System.Collections.Generic.IEqualityComparer' because it is not a delegate type" Any ideas how could I fix it? (I know I could iterate through and fill the dict one element at a time, but I simply want to use something more elegant)

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• Exposing a "dumbed-down", read-only instance of a Model in GAE

  - by Blixt

  Does anyone know a clever way, in Google App Engine, to return a wrapped Model instance that only exposes a few of the original properties, and does not allow saving the instance back to the datastore? I'm not looking for ways of actually enforcing these rules, obviously it'll still be possible to change the instance by digging through its __dict__ etc. I just want a way to avoid accidental exposure/changing of data. My initial thought was to do this (I want to do this for a public version of a User model): class ReadOnlyUser(db.Model): display_name = db.StringProperty() @classmethod def kind(cls): return 'User' def put(self): raise SomeError() Unfortunately, GAE maps the kind to a class early on, so if I do ReadOnlyUser.get_by_id(1) I will actually get a User instance back, not a ReadOnlyUser instance.

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• may be python error!!!

  - by bahar

  Hi I'm not familiar with python, I just want to check something so I tried to run a .py code in linux so I wrote : ./waf wifi-olsr-flowmon --plot which is a .py program after that whatever I want to run just see these error: /home/bahar/Desktop/ns/ns-allinone-3.9/ns-allinone-3.9/ns-3.9/wscript: error: Traceback (most recent call last): File "/home/bahar/Desktop/ns/ns-allinone-3.9/ns-allinone-3.9/ns-3.9/.waf-1.5.16-e6d03192b5ddfa5ef2c8d65308e48e42/wafadmin/Utils.py", line 197, in load_module exec(compile(code,file_path,'exec'),module.__dict__) File "/home/bahar/Desktop/ns/ns-allinone-3.9/ns-allinone-3.9/ns-3.9/wscript", line 32, in <module> import cflags # override the build profiles from waf ImportError: No module named cflags I dont know what does it mean or why it happened, would you please tell me what is the problem . Bests

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• (Python) algorithm to randomly select a key based on proportionality/weight

  - by LaundroMat

  Hi - I'm a bit at a loss as to how to find a clean algorithm for doing the following: Suppose I have a dict k: >>> k = {'A': 68, 'B': 62, 'C': 47, 'D': 16, 'E': 81} I now want to randomly select one of these keys, based on the 'weight' they have in the total (i.e. sum) amount of keys. >>> sum(k.values()) >>> 274 So that there's a >>> 68.0/274.0 >>> 0.24817518248175183 24.81% percent change that A is selected. How would you write an algorithm that takes care of this? In other words, that makes sure that on 10.000 random picks, A will be selected 2.481 times?

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• Efficient way to combine results of two database queries.

  - by ensnare

  I have two tables on different servers, and I'd like some help finding an efficient way to combine and match the datasets. Here's an example: From server 1, which holds our stories, I perform a query like: query = """SELECT author_id, title, text FROM stories ORDER BY timestamp_created DESC LIMIT 10 """ results = DB.getAll(query) for i in range(len(results)): #Build a string of author_ids, e.g. '1314,4134,2624,2342' But, I'd like to fetch some info about each author_id from server 2: query = """SELECT id, avatar_url FROM members WHERE id IN (%s) """ values = (uid_list) results = DB.getAll(query, values) Now I need some way to combine these two queries so I have a dict that has the story as well as avatar_url and member_id. If this data were on one server, it would be a simple join that would look like: SELECT * FROM members, stories WHERE members.id = stories.author_id But since we store the data on multiple servers, this is not possible. What is the most efficient way to do this? Thanks.

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• Converting human readable date into integer values

  - by kahrn

  Hello all, I am looking to do something really simple. Merely convert a string, such as 'december' into something I can use with MySQL (such as '12'). At the moment I use a dict, month_map = { 'december': '12', 'november': '11', 'october': '10', 'september': '09', 'august': '08', 'july': '07', 'june': '06', 'may': '05', 'april': '04', 'march': '03', 'february': '02', 'january': '01' } and then month_map.get('december'). Does any function already exist within the standard python modules that can achieve this? Apologies if this has already been asked.. the questions I have found using search seem a little different.

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• Get Python 2.7's 'json' to not throw an exception when it encounters random byte strings

  - by Chris Dutrow

  Trying to encode a a dict object into json using Python 2.7's json (ie: import json). The object has some byte strings in it that are "pickled" data using cPickle, so for json's purposes, they are basically random byte strings. I was using django.utils's simplejson and this worked fine. But I recently switched to Python 2.7 on google app engine and they don't seem to have simplejson available anymore. Now that I am using json, it throws an exception when it encounters bytes that aren't part of UTF-8. The error that I'm getting is: UnicodeDecodeError: 'utf8' codec can't decode byte 0x80 in position 0: invalid start byte It would be nice if it printed out a string of the character codes like the debugging might do, ie: \u0002]q\u0000U\u001201. But I really don't much care how it handles this data just as long as it doesn't throw an exception and continues serializing the information that it does recognize. How can I make this happen? Thanks!

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• Python: NameError: 'self' is not defined

  - by Rosarch

  I must be doing something stupid. I'm running this in Google App Engine: def render(self, template_name, template_data): path = os.path.join(os.path.dirname(__file__), 'static/templates/%s.html' % template_name) self.response.out.write(template.render(path, template_data)) This gives an error: Traceback (most recent call last): File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 3192, in _HandleRequest self._Dispatch(dispatcher, self.rfile, outfile, env_dict) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 3135, in _Dispatch base_env_dict=env_dict) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 516, in Dispatch base_env_dict=base_env_dict) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 2394, in Dispatch self._module_dict) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 2304, in ExecuteCGI reset_modules = exec_script(handler_path, cgi_path, hook) File "C:\Program Files\Google\google_appengine\google\appengine\tools\dev_appserver.py", line 2200, in ExecuteOrImportScript exec module_code in script_module.__dict__ File "main.py", line 22, in <module> class MainHandler(webapp.RequestHandler): File "main.py", line 38, in MainHandler self.writeOut(template.render(path, template_data)) NameError: name 'self' is not defined What am I doing wrong?

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• Globals across modules

  - by Coder1

  Wow, this seems so basic, but I can't get it to work. All I need to do is store a global dict which can be accessed and modified from other modules & threads. What's the "best practices" way of achieving this? test.py import testmodule class MyClassA(): def __init__(self, id): self.id = id if __name__ == '__main__': global classa_dict classa_dict = {} classa_dict[1] = MyClassA(1) classa_dict[2] = MyClassA(2) testing = testmodule.TestModule() testmodule.py class TestModule(): def __init__(self): global classa_dict print classa_dict[2] output $ python test.py Traceback (most recent call last): File "test.py", line 13, in <module> testing = testmodule.TestModule() File "/path/to/project/testmodule.py", line 4, in __init__ print classa_dict[2] NameError: global name 'classa_dict' is not defined

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• Django model class and custom property

  - by dArignac

  Howdy - today a weird problem occured to me: I have a modle class in Django and added a custom property to it that shall not be saved into the database and therefore is not represent in the models structure: class Category(models.Model): groups = models.ManyToManyField(Group) title = defaultdict() Now, when I'm within the shell or writing a test and I do the following: c1 = Category.objects.create() c1.title['de'] = 'german title' print c1.title['de'] # prints "german title" c2 = Category.objects.create() print c2.title['de'] # prints "german title" <-- WTF? It seems that 'title' is kind of global. If I change title to a simple string it works as expected, so it has to do something with the dict? I also tried setting title as a property: title = property(_title) But that did not work, too. So, how can I solve this? Thank you in advance! enter code here

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• IDL-like parser that turns a document definition into powerful classes?

  - by paniq

  I am looking for an IDL-like (or whatever) translator which turns a DOM- or JSON-like document definition into classes which are accessible from both C++ and Python, within the same application expose document properties as ints, floats, strings, binary blobs and compounds: array, string dict (both nestable) (basically the JSON type feature set) allow changes to be tracked to refresh views of an editing UI provide a change history to enable undo/redo operations can be serialized to and from JSON (can also be some kind of binary format) allow to keep large data chunks on disk, with parts only loaded on demand provide non-blocking thread-safe read/write access to exchange data with realtime threads allow multiple editors in different processes (or even on different machines) to view and modify the document The thing that comes closest so far is the Blender 2.5 DNA/RNA system, but it's not available as a separate library, and badly documented. I'm most of all trying to make sure that such a lib does not exist yet, so I know my time is not wasted when I start to design and write such a thing. It's supposed to provide a great foundation to write editing UI components.

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• Java - Optimize finding a string in a list

  - by Mark

  I have an ArrayList of objects where each object contains a string 'word' and a date. I need to check to see if the date has passed for a list of 500 words. The ArrayList could contain up to a million words and dates. The dates I store as integers, so the problem I have is attempting to find the word I am looking for in the ArrayList. Is there a way to make this faster? In python I have a dict and mWords['foo'] is a simple lookup without looping through the whole 1 million items in the mWords array. Is there something like this in java? for (int i = 0; i < mWords.size(); i++) { if ( word == mWords.get(i).word ) { mLastFindIndex = i; return mWords.get(i); } }

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• Is this a good approach to execute a list of operations on a data structure in Python?

  - by Sridhar Iyer

  I have a dictionary of data, the key is the file name and the value is another dictionary of its attribute values. Now I'd like to pass this data structure to various functions, each of which runs some test on the attribute and returns True/False. One approach would be to call each function one by one explicitly from the main code. However I can do something like this: #MYmodule.py class Mymodule: def MYfunc1(self): ... def MYfunc2(self): ... #main.py import Mymodule ... #fill the data structure ... #Now call all the functions in Mymodule one by one for funcs in dir(Mymodule): if funcs[:2]=='MY': result=Mymodule.__dict__.get(funcs)(dataStructure) The advantage of this approach is that implementation of main class needn't change when I add more logic/tests to MYmodule. Is this a good way to solve the problem at hand? Are there better alternatives to this solution?

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• Python Class Variables Question

  - by zyq524

  I have some doubt about python's class variables. As my understanding, if I define a class variable, which is declared outside the init() function, this variable will create only once as a static variable in C++. This seems right for some python types, for instance, dict and list type, but for those base type, e.g. int,float, is not the same. For example: class A: dict1={} list1=list() int1=3 def add_stuff(self, k, v): self.dict1[k]=v self.list1.append(k) self.int1=k def print_stuff(self): print self.dict1,self.list1,self.int1 a1 = A() a1.add_stuff(1, 2) a1.print_stuff() a2=A() a2.print_stuff() The output is: {1: 2} [1] 1 {1: 2} [1] 3 I understand the results of dict1 and list1, but why does int1 behavior different?

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• Using regular expressions with Dojo data.fetch?

  - by Dfowj

  I'm trying to use the below code to fetch a regular expression like this /[computer]{3,8}/(what i think is any words containing the letters in computer ranging from 3 to 8 letters long) from a database (which i know is being loaded correctly). When i fetch, i get 10 results, all the same word... "Adenauer" var base = "computer"; var baseRE = '/[' + base + ']{' + this.minLength + ',' + base.length + '}/'; this.dict.fetch({query: {word:baseRE}, onComplete: onLoadWords, onError: function(err) { console.log(err); }}); Any ideas what im doing wrong?

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• How to get a variable name as a string in Python?

  - by e-satis

  I would like to be able to get the name of a variable as a string but I don't know if Python has that much introspection capabilities. Something like: >>> print(my_var.__name__) 'my_var' I want to do that because I have a bunch of vars I'd like to turn into a dictionary like : bar=True foo=False >>> my_dict=dict(bar=bar, foo=foo) >>> print mydict >>> print my_dict {'foo': False, 'bar': True} But I'd like something more automatic than that. Python have locals() and vars(), so I guess there is a way.

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• Is "programmatically" a word? [closed]

  - by Lo'oris

  I can't find it on any of the online dictionaries I know: dict.org, word reference, urban dictionary, oxford paravia, garzanti. To my ears of a non-native speaker, it sounds horrible. Actually it sounds like a word made-up by another non-native speaker that wanted to say something, didn't know how, and just hacked in a word of his language. The only place I've read it other then user-created-content is the android documentation, so this might or might not be related. Do you happen to know where did it start to be used, why by did it spread so much, what does it really mean?

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• TypeError: object not callable when making instance

  - by TSM

  I've searched around other threads with similar questions, but I'm not finding the answer. Basically, I have a class: import Android_Class class Android_Revision(object): def __init__(self): # dict for storing the classes in this revision # (format {name : classObject}): self.Classes = {} self.WorkingClass = Android_Class() self.RevisionNumber = '' def __call__(self): print "Called" def make_Class(self, name): newClass = Android_Class(name) self.Classes.update({name : newClass}) self.WorkingClass = newClass def set_Class(self, name): if not(self.Classes.has_key(name)): newClass = Android_Class(name) self.Classes.update({name : newClass}) self.WorkingClass = self.Classes.get(name) I'm trying to make an instance of this class: Revision = Android_Revision() and that's when I'm getting the error. I'm confused because I have another situation where I'm doing almost the exact same thing, and it's working fine. I can't figure out what differences between the two would lead to this error. Thanks.

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• Value [...] not a valid choice, django-updown

  - by tamara

  I am trying to implemet django-updown https://github.com/weluse/django-updown. When I try to add vote trough the admin panel it says Value 1 not a valid choice. This is the models.py from the application: _SCORE_TYPE_CHOICES = ( ('-1', 'DISLIKE'), ('1', 'LIKE'), ) SCORE_TYPES = dict((value, key) for key, value in _SCORE_TYPE_CHOICES) class Vote(models.Model): content_type = models.ForeignKey(ContentType, related_name="updown_votes") object_id = models.PositiveIntegerField() key = models.CharField(max_length=32) score = models.SmallIntegerField(choices=_SCORE_TYPE_CHOICES) user = models.ForeignKey(User, blank=True, null=True, related_name="updown_votes") ip_address = models.IPAddressField() date_added = models.DateTimeField(default=datetime.datetime.now, editable=False) date_changed = models.DateTimeField(default=datetime.datetime.now, editable=False) Do you have an idea what could be wrong?

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• speeding up parsing of files

  - by user248237

  the following function parses a CSV file into a list of dictionaries, where each element in the list is a dictionary where the values are indexed by the header of the file (assumed to be the first line.) this function is very very slow, taking ~6 seconds for a file that's relatively small (less than 30,000 lines.) how can I speed it up? def csv2dictlist_raw(filename, delimiter='\t'): f = open(filename) header_line = f.readline().strip() header_fields = header_line.split(delimiter) dictlist = [] # convert data to list of dictionaries for line in f: values = map(tryEval, line.strip().split(delimiter)) dictline = dict(zip(header_fields, values)) dictlist.append(dictline) return (dictlist, header_fields) thanks.

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• Why do dicts of defaultdict(int)'s use so much memory? (and other simple python performance question

  - by dukhat

  import numpy as num from collections import defaultdict topKeys = range(16384) keys = range(8192) table = dict((k,defaultdict(int)) for k in topKeys) dat = num.zeros((16384,8192), dtype="int32") print "looping begins" #how much memory should this use? I think it shouldn't use more that a few #times the memory required to hold (16384*8192) int32's (512 mb), but #it uses 11 GB! for k in topKeys: for j in keys: dat[k,j] = table[k][j] print "done" What is going on here? Furthermore, this similar script takes eons to run compared to the first one, and also uses an absurd quantity of memory. topKeys = range(16384) keys = range(8192) table = [(j,0) for k in topKeys for j in keys] I guess python ints might be 64 bit ints, which would account for some of this, but do these relatively natural and simple constructions really produce such a massive overhead? I guess these scripts show that they do, so my question is: what exactly is causing the high memory usage in the first script and the long runtime and high memory usage of the second script and is there any way to avoid these costs?

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• String manipulation appears to be inefficient

  - by user2964780

  I think my code is too inefficient. I'm guessing it has something to do with using strings, though I'm unsure. Here is the code: genome = FASTAdata[1] genomeLength = len(genome); # Hash table holding all the k-mers we will come across kmers = dict() # We go through all the possible k-mers by index for outer in range (0, genomeLength-1): for inner in range (outer+2, outer+22): substring = genome[outer:inner] if substring in kmers: # if we already have this substring on record, increase its value (count of num of appearances) by 1 kmers[substring] += 1 else: kmers[substring] = 1 # otherwise record that it's here once This is to search through all substrings of length at most 20. Now this code seems to take pretty forever and never terminate, so something has to be wrong here. Is using [:] on strings causing the huge overhead? And if so, what can I replace it with? And for clarity the file in question is nearly 200mb, so pretty big.

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