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  • How do I do a semijoin using SQLAlchemy?

    - by Jason Baker
    http://en.wikipedia.org/wiki/Relational_algebra#Semijoin Let's say that I have two tables: A and B. I want to make a query that would work similarly to the following SQL statement using the SQLAlchemy orm: SELECT A.* FROM A, B WHERE A.id = B.id AND B.type = 'some type'; The thing is that I'm trying to separate out A and B's logic into different places. So I'd like to make two queries that I can define in separate places: one where A uses B as a subquery, but only returns rows from A. I'm sure this is fairly easy to do, but an example would be nice if someone could show me.

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  • read the dictionary value from array

    - by ben martin
    CALORIES = \ { 'Beef' : 200, \ 'Chicken' : 140, \ } class Food(): __slots__ = ( 'cal' # Calories ) def mkFood( name ): """Create and return a newly initialized Food item""" result = Food() result.cal = calorie in dict(CALORIES[1]) return result Is that a proper way to the value of the target item in Calories? Like getting 200, 140, such like that. result.cal = calorie in dict(CALORIES[1])

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  • make a tree based on the key of each element in list.

    - by cocobear
    >>> s [{'000000': [['apple', 'pear']]}, {'100000': ['good', 'bad']}, {'200000': ['yeah', 'ogg']}, {'300000': [['foo', 'foo']]}, {'310000': [['#'], ['#']]}, {'320000': ['$', ['1']]}, {'321000': [['abc', 'abc']]}, {'322000': [['#'], ['#']]}, {'400000': [['yeah', 'baby']]}] >>> for i in s: ... print i ... {'000000': [['apple', 'pear']]} {'100000': ['good', 'bad']} {'200000': ['yeah', 'ogg']} {'300000': [['foo', 'foo']]} {'310000': [['#'], ['#']]} {'320000': ['$', ['1']]} {'321000': [['abc', 'abc']]} {'322000': [['#'], ['#']]} {'400000': [['yeah', 'baby']]} i want to make a tree based on the key of each element in list. result in logic will be: {'000000': [['apple', 'pear']]} {'100000': ['good', 'bad']} {'200000': ['yeah', 'ogg']} {'300000': [['foo', 'foo']]} {'310000': [['#'], ['#']]} {'320000': ['$', ['1']]} {'321000': [['abc', 'abc']]} {'322000': [['#'], ['#']]} {'400000': [['yeah', 'baby']]} perhaps a nested list can implement this or I need a tree type?

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  • Calculating the null space of a matrix

    - by Ainsworth
    I'm attempting to solve a set of equations of the form Ax = 0. A is known 6x6 matrix and I've written the below code using SVD to get the vector x which works to a certain extent. The answer is approximately correct but not good enough to be useful to me, how can I improve the precision of the calculation? Lowering eps below 1.e-4 causes the function to fail. from numpy.linalg import * from numpy import * A = matrix([[0.624010149127497 ,0.020915658603923 ,0.838082638087629 ,62.0778180312547 ,-0.336 ,0], [0.669649399820597 ,0.344105317421833 ,0.0543868015800246 ,49.0194290212841 ,-0.267 ,0], [0.473153758252885 ,0.366893577716959 ,0.924972565581684 ,186.071352614705 ,-1 ,0], [0.0759305208803158 ,0.356365401030535 ,0.126682113674883 ,175.292109352674 ,0 ,-5.201], [0.91160934274653 ,0.32447818779582 ,0.741382053883291 ,0.11536775372698 ,0 ,-0.034], [0.480860406786873 ,0.903499596111067 ,0.542581424762866 ,32.782593418975 ,0 ,-1]]) def null(A, eps=1e-3): u,s,vh = svd(A,full_matrices=1,compute_uv=1) null_space = compress(s <= eps, vh, axis=0) return null_space.T NS = null(A) print "Null space equals ",NS,"\n" print dot(A,NS)

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  • Change|Assign parent for the Model instance on Google App Engine Datastore

    - by Vladimir Prudnikov
    Is it possible to change or assign new parent to the Model instance that already in datastore? For example I need something like this task = db.get(db.Key(task_key)) project = db.get(db.Key(project_key)) task.parent = project task.put() but it doesn't works this way because task.parent is built-in method. I was thinking about creating a new Key instance for the task but there is no way to change key as well. Any thoughts?

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  • UDP security and identifying incoming data.

    - by Charles
    I have been creating an application using UDP for transmitting and receiving information. The problem I am running into is security. Right now I am using the IP/socketid in determining what data belongs to whom. However, I have been reading about how people could simply spoof their IP, then just send data as a specific IP. So this seems to be the wrong way to do it (insecure). So how else am I suppose to identify what data belongs to what users? For instance you have 10 users connected, all have specific data. The server would need to match the user data to this data we received. The only way I can see to do this is to use some sort of client/server key system and encrypt the data. I am curious as to how other applications (or games, since that's what this application is) make sure their data is genuine. Also there is the fact that encryption takes much longer to process than unencrypted. Although I am not sure by how much it will affect performance. Any information would be appreciated. Thanks.

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  • Reordering fields in Django model

    - by Alex Lebedev
    I want to add few fields to every model in my django application. This time it's created_at, updated_at and notes. Duplicating code for every of 20+ models seems dumb. So, I decided to use abstract base class which would add these fields. The problem is that fields inherited from abstract base class come first in the field list in admin. Declaring field order for every ModelAdmin class is not an option, it's even more duplicate code than with manual field declaration. In my final solution, I modified model constructor to reorder fields in _meta before creating new instance: class MyModel(models.Model): # Service fields notes = my_fields.NotesField() created_at = models.DateTimeField(auto_now_add=True) updated_at = models.DateTimeField(auto_now=True) class Meta: abstract = True last_fields = ("notes", "created_at", "updated_at") def __init__(self, *args, **kwargs): new_order = [f.name for f in self._meta.fields] for field in self.last_fields: new_order.remove(field) new_order.append(field) self._meta._field_name_cache.sort(key=lambda x: new_order.index(x.name)) super(TwangooModel, self).__init__(*args, **kwargs) class ModelA(MyModel): field1 = models.CharField() field2 = models.CharField() #etc ... It works as intended, but I'm wondering, is there a better way to acheive my goal?

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  • reading specific lines from a file

    - by MacUsers
    What's the best way of reading only the specific lines (based on matching text) from a file? This is what I'm doing now: match_txt = "lhcb" for inFile in os.listdir('.'): readFile = open(inFile, 'r') lines = readFile.readlines() readFile.close() for line in lines: if line.find(match_txt)==0: #< do stuff here > i.e. I'm reading the lines, only with "lhcb" in it, from all the files in the present directory one by one. Is it the best way of doing that? Can it be done without loading the whole file in the memory in the first place?

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  • Strip text except from the contents of a tag

    - by myle
    The opposite may be achieved using pyparsing as follows: from pyparsing import Suppress, replaceWith, makeHTMLTags, SkipTo #... removeText = replaceWith("") scriptOpen, scriptClose = makeHTMLTags("script") scriptBody = scriptOpen + SkipTo(scriptClose) + scriptClose scriptBody.setParseAction(removeText) data = (scriptBody).transformString(data) How could I keep the contents of the tag "table"?

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  • How to access the calling source line from interactive shell

    - by TJD
    I want to make a function that can determine the source code of how it was called. I'm aware of how to do this generally with the inspect module. For example, this question, works well and provides my desired output in the lines variable as shown below: def hello(x): frame,filename,line_number,function_name,lines,index=\ inspect.getouterframes(inspect.currentframe())[1] print(frame,filename,line_number,function_name,lines,index) The problem is that this solution doesn't work in an interactive command line session. For example, from a command line, the result looks like: >>> y = hello(7) (<frame object at 0x01ECA9E8>, '<stdin>', 1, '<module>', None, None) The problem is that the source file is '<stdin>', so the lines variable is None. How can I access the calling line to find the result containing the string y = hello(7) during an interactive session?

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  • Many-to-one relationship in SQLAlchemy

    - by Arrieta
    This is a beginner-level question. I have a catalog of mtypes: mtype_id name 1 'mtype1' 2 'mtype2' [etc] and a catalog of Objects, which must have an associated mtype: obj_id mtype_id name 1 1 'obj1' 2 1 'obj2' 3 2 'obj3' [etc] I am trying to do this in SQLAlchemy by creating the following schemas: mtypes_table = Table('mtypes', metadata, Column('mtype_id', Integer, primary_key=True), Column('name', String(50), nullable=False, unique=True), ) objs_table = Table('objects', metadata, Column('obj_id', Integer, primary_key=True), Column('mtype_id', None, ForeignKey('mtypes.mtype_id')), Column('name', String(50), nullable=False, unique=True), ) mapper(MType, mtypes_table) mapper(MyObject, objs_table, properties={'mtype':Relationship(MType, backref='objs', cascade="all, delete-orphan")} ) When I try to add a simple element like: mtype1 = MType('mtype1') obj1 = MyObject('obj1') obj1.mtype=mtype1 session.add(obj1) I get the error: AttributeError: 'NoneType' object has no attribute 'cascade_iterator' Any ideas?

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  • numpy arange with multiple intervals

    - by Heiko Westermann
    Hi, i have an numpy array which represents multiple x-intervals of a function: In [137]: x_foo Out[137]: array([211, 212, 213, 214, 215, 216, 217, 218, 940, 941, 942, 943, 944, 945, 946, 947, 948, 949, 950]) as you can see, in x_foo are two intervals: one from 211 to 218, and one from 940 to 950. these are intervals, which i want to interpolate with scipy. for this, i need to adjust the spacing, e.g "211.0 211.1 211.2 ..." which you would normaly do with: arange( x_foo[0], x_foo[-1], 0.1 ) in the case of multiple intervals, this is not possible. so heres my question: is there a numpy-thonic way to do this in array-style? or do i need to write a function which loops over the whole array and split if the difference is 1? thanks!

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  • How to insert several thousand columns into sqlite3?

    - by user291071
    Similar to my last question, but I ran into problem lets say I have a simple dictionary like below but its Big, when I try inserting a big dictionary using the methods below I get operational error for the c.execute(schema) for too many columns so what should be my alternate method to populate an sql databases columns? Using the alter table command and add each one individually? import sqlite3 con = sqlite3.connect('simple.db') c = con.cursor() dic = { 'x1':{'y1':1.0,'y2':0.0}, 'x2':{'y1':0.0,'y2':2.0,'joe bla':1.5}, 'x3':{'y2':2.0,'y3 45 etc':1.5} } # 1. Find the unique column names. columns = set() for _, cols in dic.items(): for key, _ in cols.items(): columns.add(key) # 2. Create the schema. col_defs = [ # Start with the column for our key name '"row_name" VARCHAR(2) NOT NULL PRIMARY KEY' ] for column in columns: col_defs.append('"%s" REAL NULL' % column) schema = "CREATE TABLE simple (%s);" % ",".join(col_defs) c.execute(schema) # 3. Loop through each row for row_name, cols in dic.items(): # Compile the data we have for this row. col_names = cols.keys() col_values = [str(val) for val in cols.values()] # Insert it. sql = 'INSERT INTO simple ("row_name", "%s") VALUES ("%s", "%s");' % ( '","'.join(col_names), row_name, '","'.join(col_values) )

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  • How To Collapse Just One Field in Django Admin?

    - by Apreche
    The django admin allows you to specify fieldsets. You properly structure a tuple that groups different fields together. You can also specify classes for certain groups of fields. One of those classes is collapse, which will hide the field under a collapsable area. This is good for hiding rarely used or advanced fields to keep the UI clean. However, I have a situation where I want to hide just one lonesome field on many different apps. This will be a lot of typing to create a full fieldset specification in every admin.py file just to put one field into the collapsed area. It also creates a difficult maintenance situation because I will have to edit the fieldset every time I edit the associated model. I can easily exclude the field entirely using the exclude option. I want something similar for collapse. Is this possible?

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  • Problems with 'while' loop and 'for' loop when reading through file

    - by David Beckham
    I wasted plenty of hours trying to figure out the problem but no luck. Tried asking the TA at my school, but he was useless. I am a beginner and I know there are a lot of mistakes in it, so it would be great if I can get some detail explanation as well. Anyways, basically what I am trying to do with the following function is: Use while loop to check and see if random_string is in TEXT, if not return NoneType if yes, then use a for loop to read lines from that TEXT and put it in list, l1. then, write an if statement to see if random_string is in l1. if it is, then do some calculations. else read the next line Finally, return the calculations as a whole. TEXT = open('randomfile.txt') def random (TEXT, random_string): while random_string in TEXT: for lines in TEXT: l1=TEXT.readline().rsplit() if random_string in l1: ''' do some calculations ''' else: TEXT.readline() #read next line??? return #calculations return None

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  • Django throws 404 at generic views

    - by x0rg
    I'm trying to get the generic views for a date-based archive working in django. I defined the urls as described in a tutorial, but django returns a 404 error whenever I want to access an url with a variable (such as month or year) in it. It don't even produces a TemplateDoesNotExist-execption. Normal urls without variables work fine. Here's my urlconf: from django.conf.urls.defaults import * from zurichlive.zhl.models import Event info_dict = { 'queryset': Event.objects.all(), 'date_field': 'date', 'allow_future': 'True', } urlpatterns += patterns('django.views.generic.date_based', (r'events/(?P<year>d{4})/(?P<month>[a-z]{3})/(?P<day>w{1,2})/(?P<slug>[-w]+)/$', 'object_detail', dict(info_dict, slug_field='slug',template_name='archive/detail.html')), (r'^events/(?P<year>d{4})/(?P<month>[a-z]{3})/(?P<day>w{1,2})/(?P<slug>[-w]+)/$', 'object_detail', dict(info_dict, template_name='archive/list.html')), (r'^events/(?P<year>d{4})/(?P<month>[a-z]{3})/(?P<day>w{1,2})/$','archive_day',dict(info_dict,template_name='archive/list.html')), (r'^events/(?P<year>d{4})/(?P<month>[a-z]{3})/$','archive_month', dict(info_dict, template_name='archive/list.html')), (r'^events/(?P<year>)/$','archive_year', dict(info_dict, template_name='archive/list.html')), (r'^events/$','archive_index', dict(info_dict, template_name='archive/list.html')), ) When I access /events/2010/may/12/this-is-a-slug I should get to the detail.html template, but instead I get a 404. What am I doing wrong?

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  • Time difference in seconds (as a floating point)

    - by pocoa
    >>> from datetime import datetime >>> t1 = datetime.now() >>> t2 = datetime.now() >>> delta = t2 - t1 >>> delta.seconds 7 >>> delta.microseconds 631000 Is there any way to get that as 7.631000 ? I can use time module, but I also need that t1 and t2 variables as DateTime objects. So if there is a way to do it with datettime, that would be great.

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  • How to do a back-reference on Google Webapp?

    - by jCuga
    I'm trying to access an object that is linked to by a db.ReferenceProperty in Google app engine. here's the model's code: class InquiryQuestion(db.Model): inquiry_ref = db.ReferenceProperty(reference_class=GiftInquiry, required=True, collection_name="inquiry_ref") And I am trying to access it in the following way: linkedObject = question.inquiry_ref and then linkedKey = linkedObject.key but it's not working. Can anyone please help?

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  • pyplot.scatter changes the data limits of the axis

    - by Erotemic
    I have some code which plots some points. I substituted ax.scatter for ax.plot so I could control the color of each point individually. However when I make this change the axis x and y ranges seem to increase. I can't pinpoint why this is happening. The only thing I've changed is plot to scatter. This code makes an axis that is too big ax.scatter(x, y, c=color_list, s=pts_size, marker='o', edgecolor='none') #ax.plot(x, y, linestyle='None', marker='o', markerfacecolor=pts_color, markersize=pts_size, markeredgewidth=0) This code does the right thing (but I can't control the color) #ax.scatter(x, y, c=color_list, s=pts_size, marker='o', edgecolor='none') ax.plot(x, y, linestyle='None', marker='o', markerfacecolor=pts_color, markersize=pts_size, markeredgewidth=0) Is there a way I can call scatter such that it doesn't mess with my current axis limits?

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