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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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  • Pyjamas import statements

    - by Gordon Worley
    I'm starting to use Pyjamas and I'm running into some annoyances. I have to import a lot of stuff to make a script work well. For example, to make a button I need to first from pyjamas.ui.Button import Button and then I can use Button. Note that import pyjamas.ui.Button and then using Button.Button doesn't work (results in errors when you build to JavaScript, at least in 0.7pre1). Does anyone have a better example of a good way to do the import statements in Pyjamas than what the Pyjamas folks have on their site? Doing things their way is possible, but ugly and overly complicated from my perspective, especially when you want to use a dozen or more ui components.

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  • Appengine Model SelfReferenceProperty and parent child relationship

    - by GeekTantra
    I have a scenario in which I need a self reference property as follow: class Post(db.Model): creator = db.UserProperty() post_title = db.StringProperty(required=True) post_status = db.StringProperty(required=True, choices=['draft', 'published']) post_parent = db.SelfReferenceProperty() Now, I want ensure that an entity shouldn't be its own parent and a child of an entity cannot be its parent. How can I ensure this kind of a relationship in the PostForm model form and the Post model.

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  • How to invert alternate bits of a number

    - by Cupidvogel
    The problem is how to invert alternate bits of a number, starting from the LSB. Currently what I am doing is first doing a count = -1 while n: n >>= 1 count += 1 to first find the position of the leftmost set bit, then running a loop to invert every alternate bit: i = 0 while i <= count: num ^= 1<<i i += 2 Is there a quick hack solution instead of this rather boring loop solution? Of course, the solution can't make any asumption about the size of the integer.

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  • Finding out event that called a CGI script

    - by Acorn
    What I want is to be able to make my CGI script do different things depending on what action initiated the calling of the script. For example, if one button is pressed, a database is cleared. If another button is pressed, a form is submitted and that data is added to the database. Should I be doing something like adding the name of the form/button to the end of the POST data submitted in jQuery and then .poping it off in the script? Or is there some other data that's already sent in the POST that I could get from FieldStorage that would give me the information I need to decide what the script should do when it's called? And what if I wasn't using javascript? Would I have to have a hidden field that gets submitted with the name of the form/button? Or is it best to use a different target script for each button on a page?

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  • Tkinter after that survives clock rewinding.

    - by Oren
    I noticed that in my version of Tkinter, the after() call does not survive system clock rewinding. If the after(x, func) was called, and the system clock was rewinded, func will be called only after the clock returned to its time before the rewind + x milliseconds. I assume this is because Tkinter uses the system-clock instead of the "time.clock" (the amount of time that the program is running). I tested it only on windows, and maybe its because I have an old version of Tkinter. I want my App to work on computers that synchronize their clock from the network... Does anyone have a simple solution?

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  • What does this `_time_independent_equals` mean?

    - by Satoru.Logic
    In the tornado.web module there is a function called _time_independent_equals: def _time_independent_equals(a, b): if len(a) != len(b): return False result = 0 for x, y in zip(a, b): result |= ord(x) ^ ord(y) return result == 0 It is used to compare secure cookie signatures, and thus the name. But regarding the implementation of this function, is it just a complex way to say a==b?

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  • MongoDB lists with paginations?

    - by Timmy
    for documents with lists with pagination, is it better to embed or use reference? im reading the custom type "SONManipulator" and it appears to transform every thing on retrieval, even the sub docs. i want to keep the list in the document sorted, should this impact anything?

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  • how to fetch more than 1000 entities NON keybased?

    - by user291071
    If I should be approaching this problem through a different method, please suggest so. I am creating an item based collaborative filter. I populate the db with the LinkRating2 class and for each link there are more than a 1000 users that I need to call and collect their ratings to perform calculations which I then use to create another table. So I need to call more than 1000 entities for a given link. For instance lets say there are over a 1000 users rated 'link1' there will be over a 1000 instances of this class for the given link property that I need to call. How would I complete this example? class LinkRating2(db.Model): user = db.StringProperty() link = db.StringProperty() rating2 = db.FloatProperty() query =LinkRating2.all() link1 = 'link string name' a = query.filter('link = ', link1) aa = a.fetch(1000)##how would i get more than 1000 for a given link1 as shown? ##keybased over 1000 in other post example i need method for a subset though not key class MyModel(db.Expando): @classmethod def count_all(cls): """ Count *all* of the rows (without maxing out at 1000) """ count = 0 query = cls.all().order('__key__') while count % 1000 == 0: current_count = query.count() if current_count == 0: break count += current_count if current_count == 1000: last_key = query.fetch(1, 999)[0].key() query = query.filter('__key__ > ', last_key) return count

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  • Is it possible to bulk load an NDB child Entity in GAE?

    - by hmacread
    At some point in the future I may need to bulk load migration data (i.e. from a CSV). Has anyone had exceptions raised doing the following? Also is there any change in behaviour if the ndb.put_multi() function is used? from google.appengine.ext import ndb while True: if not id: break id, name = read_csv_row(readline()) x = X(parent=ndb.Key('Y','static_id') x.id, x.name = id, name x.put() class X(ndb.Model): id = StringProperty() name = StringProperty() class Y(ndb.Model): pass def read_csv_row(line): """returns tuple"""

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  • How can I identify an element from a list within another list

    - by Alex
    I have been trying to make a block of code that finds the index of the largest bid for each item. Then I was going to use the index as a way to identify the person who paid that much moneys name. However no matter what i try I can't link the person and what they have gained from the auction together. Here is the code I have been writing: It has to be able to work with any information inputted def sealedBids(): n = int(input('\nHow many people are in the group? ')) z = 0 g = [] s = [] b = [] f = [] w = []#goes by number of items q = [] while z < n: b.append([]) z = z + 1 z = 0 while z < n: g.append(input('Enter a bidders name: ')) z = z + 1 z = 0 i = int(input('How many items are being bid on?')) while z < i: s.append(input('Enter the name of an item: ')) w.append(z) z = z + 1 z = 0 for j in range(n):#specifies which persons bids your taking for k in range(i):#specifies which item is being bid on b[j].append(int(input('How much money has {0} bid on the {1}? '.format(g[j], s[k])))) print(' ') for j in range(n):#calculates fair share f.append(sum(b[j])/n) for j in range(i):#identifies which quantity of money was the largest for each item for k in range(n): if w[j] < b[k][j]: w[j] = b[k][j] q.append(k) any advice is much appreciated.

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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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  • poplib and email module will not reloop through a message if it has alread read it

    - by user1440925
    I'm currently trying to write a script that gets messages from my gmail account but I'm noticing a problem. If poplib loops through a message in my inbox it will never loop through it again. Here is my code import poplib, string, email user = "[email protected]" password = "p0ckystyx" message = "" mail = poplib.POP3_SSL('pop.gmail.com') mail.user(user) mail.pass_(password) iMessageCount = len(mail.list()[1]) message = "" msg = mail.retr(iMessageCount) str = string.join(msg[1], "\n") frmMail = email.message_from_string(str) for part in frmMail.walk(): if part.get_content_type() == "text/plain": print part.get_payload() mail.quit() Every time I run this script it goes to the next newest email and just skips over the email that was shown last time it was run.

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  • better for-loop syntax for detecting empty sequences?

    - by Dmitry Beransky
    Hi, Is there a better way to write the following: row_counter = 0 for item in iterable_sequence: # do stuff with the item counter += 1 if not row_counter: # handle the empty-sequence-case Please keep in mind that I can't use len(iterable_sequence) because 1) not all sequences have known lengths; 2) in some cases calling len() may trigger loading of the sequence's items into memory (as the case would be with sql query results). The reason I ask is that I'm simply curious if there is a way to make above more concise and idiomatic. What I'm looking for is along the lines of: for item in sequence: #process item *else*: #handle the empty sequence case (assuming "else" here worked only on empty sequences, which I know it doesn't)

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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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  • wxpython - Running threads sequentially without blocking GUI

    - by ryantmer
    I've got a GUI script with all my wxPython code in it, and a separate testSequences module that has a bunch of tasks that I run based on input from the GUI. The tasks take a long time to complete (from 20 seconds to 3 minutes), so I want to thread them, otherwise the GUI locks up while they're running. I also need them to run one after another, since they all use the same hardware. (My rationale behind threading is simply to prevent the GUI from locking up.) I'd like to have a "Running" message (with varying number of periods after it, i.e. "Running", "Running.", "Running..", etc.) so the user knows that progress is occurring, even though it isn't visible. I'd like this script to run the test sequences in separate threads, but sequentially, so that the second thread won't be created and run until the first is complete. Since this is kind of the opposite of the purpose of threads, I can't really find any information on how to do this... Any help would be greatly appreciated. Thanks in advance! gui.py import testSequences from threading import Thread #wxPython code for setting everything up here... for j in range(5): testThread = Thread(target=testSequences.test1) testThread.start() while testThread.isAlive(): #wait until the previous thread is complete time.sleep(0.5) i = (i+1) % 4 self.status.SetStatusText("Running"+'.'*i) testSequences.py import time def test1(): for i in range(10): print i time.sleep(1) (Obviously this isn't the actual test code, but the idea is the same.)

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  • removing elements incrementally from a list

    - by Javier
    Dear all, I've a list of float numbers and I would like to delete incrementally a set of elements in a given range of indexes, sth. like: for j in range(beginIndex, endIndex+1): print ("remove [%d] => val: %g" % (j, myList[j])) del myList[j] However, since I'm iterating over the same list, the indexes (range) are not valid any more for the new list. Does anybody has some suggestions on how to delete the elements properly? Best wishes

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  • How to execute machine language from memory?

    - by Mike Curry
    I wrote a program to compile a simple text program to a compiled executable... Is it possible that I can load an executable to memory an some how point a pc counter to the memory space at will? Here is what I made that I would like to store the programs to memory for execution on demand... Kind of wanting to make a little web language like php but compile it... Just for learning. http://spiceycurry.blogspot.com/2010/05/simple-compilable-programming-language.html

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  • Py GTK Drawing area and Rich Text Editor

    - by crashekar
    I would like to include a rich text editor in a pygtk drawing area for an application i am developing. The editor ( a small resizable widget ) should be able to move around the drawing area like a rectangle. I am not sure how to start as I am pretty new to PyGTK. thank you !

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