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  • How to pickle and unpickle objects with self-references and from a class with slots?

    - by EOL
    Is it possible to pickle an object from a class with slots, when this object references itself through one of its attributes? Here is a simple example: import weakref import pickle class my_class(object): __slots__ = ('an_int', 'ref_to_self', '__weakref__') def __init__(self): self.an_int = 42 self.ref_to_self = weakref.WeakKeyDictionary({self: 1}) # __getstate__ and __setstate__ not defined: how should this be done? if __name__ == '__main__': obj = my_class() # How to make the following work? obj_pickled = pickle.dumps(obj) obj_unpickled = pickle.loads(obj_pickled) # Self-references should be kept: print "OK?", obj_unpickled == obj_unpickled.ref_to_self.keys()[0]

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  • How do I serve a large file using Pylons?

    - by Chris R
    I am writing a Pylons-based download gateway. The gateway's client will address files by ID: /file_gw/download/1 Internally, the file itself is accessed via HTTP from an internal file server: http://internal-srv/path/to/file_1.content The files may be quite large, so I want to stream the content. I store metadata about the file in a StoredFile model object: class StoredFile(Base): id = Column(Integer, primary_key=True) name = Column(String) size = Column(Integer) content_type = Column(String) url = Column(String) Given this, what's the best (ie: most architecturally-sound, performant, et al) way to write my file_gw controller?

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  • List comprehension, map, and numpy.vectorize performance

    - by mcstrother
    I have a function foo(i) that takes an integer and takes a significant amount of time to execute. Will there be a significant performance difference between any of the following ways of initializing a: a = [foo(i) for i in xrange(100)] a = map(foo, range(100)) vfoo = numpy.vectorize(foo) a = vfoo(range(100)) (I don't care whether the output is a list or a numpy array.) Is there a better way?

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  • Preventing a security breach

    - by Wiz
    I am creating a website where you "post", and the form content is saved in a MySql database, and upon loading the page, is retrieved, similar to facebook. I construct all the posts and insert raw html into a template. The thing is, as I was testing, I noticed that I could write javascript or other HTML into the form and submit it, and upon reloading, the html or JS would treated as source code, not a post. I figured that some simple encoding would do the trick, but using is not working. Is there an efficient way to prevent this type of security hole?

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  • Web and stand-alone apps development tendency

    - by Narek
    There is a strong tendency of making web apps and even seems that very soon a lot of features will be available online so that for every day use people will have all necessary software free online and they will not need to install any software locally. Only specific (professional) tools that usually people don’t use at home will not be available as a web app. So my question, how do you imagine selling software that was necessary for everyday use and was not free (seems they can't make money any more by selling their product – no need of those products). And what disadvantages have web apps, that is to say, what is bad to use software online compared with having the same software locally (please list)? Please do not consider this question not connected with programming, as I really would like to have a little statistics from professional programmers who are aware from nowday’s tendency of software and programming. Thanks.

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  • How to save to two tables using one SQLAlchemy model

    - by Oatman
    I have an SQLAlchemy ORM class, linked to MySQL, which works great at saving the data I need down to the underlying table. However, I would like to also save the identical data to a second archive table. Here's some psudocode to try and explain what I mean my_data = Data() #An ORM Class my_data.name = "foo" #This saves just to the 'data' table session.add(my_data) #This will save it to the identical 'backup_data' table my_data_archive = my_data my_data_archive.__tablename__ = 'backup_data' session.add(my_data_archive) #And commits them both session.commit() Just a heads up, I am not interested in mapping a class to a JOIN, as in: http://www.sqlalchemy.org/docs/05/mappers.html#mapping-a-class-against-multiple-tables

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  • How to merge or copy anonymous session data into user data when user logs in?

    - by benhoyt
    This is a general question, or perhaps a request for pointers to other open source projects to look at: I'm wondering how people merge an anonymous user's session data into the authenticated user data when a user logs in. For example, someone is browsing around your websites saving various items as favourites. He's not logged in, so they're saved to an anonymous user's data. Then he logs in, and we need to merge all that data into their (possibly existing) user data. Is this done different ways in an ad-hoc fashion for different applications? Or are there some best practices or other projects people can direct me to?

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  • Django & custom auth backend (web service) + no database. How to save stuff in session?

    - by Infinity
    I've been searching here and there, and based on this answer I've put together what you see below. It works, but I need to put some stuff in the user's session, right there inside authenticate. How would I store acme_token in the user's session, so that it will get cleared if they logged out? class AcmeUserBackend(object): # Create a User object if not already in the database? create_unknown_user = False def get_user(self, username): return AcmeUser(id=username) def authenticate(self, username=None, password=None): """ Check the username/password and return an AcmeUser. """ acme_token = ask_another_site_about_creds(username, password) if acme_token: return AcmeUser(id=username) return None ################## from django.contrib.auth.models import User class AcmeUser(User): objects = None # we cannot really use this w/o local DB def save(self): """saving to DB disabled""" pass def get_group_permissions(self): """If you don't make your own permissions module, the default also will use the DB. Throw it away""" return [] # likewise with the other permission defs def get_and_delete_messages(self): """Messages are stored in the DB. Darn!""" return []

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  • Converting time period strings to value/unit pair

    - by randomtoor
    I need to parse the contents of a string that represents a time period. The format of the string is value/unit, e.g.: 1s, 60min, 24h. I would separate the actual value (an int) and unit (a str) to separated variables. At the moment I do it like this: def validate_time(time): binsize = time.strip() unit = re.sub('[0-9]','',binsize) if unit not in ['s','m','min','h','l']: print "Error: unit {0} is not valid".format(unit) sys.exit(2) tmp = re.sub('[^0-9]','',binsize) try: value = int(tmp) except ValueError: print "Error: {0} is not valid".format(time) sys.exit(2) return value,unit However, it is not ideal as things like 1m0 are also (wrongly) validated (value=10,unit=m). What is the best way to validate/parse this input?

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  • delete common dictionaries in list based on a value

    - by pythoonatic
    How would I delete all corresponding dictionaries in a list of dictionaries based on one of the dictionaries having a character in it. data = [ { 'x' : 'a', 'y' : '1' }, { 'x' : 'a', 'y' : '1/1' }, { 'x' : 'a', 'y' : '2' }, { 'x' : 'b', 'y' : '1' }, { 'x' : 'b', 'y' : '1' }, { 'x' : 'b', 'y' : '1' }, ] For example, how would I delete all of the x = a due to one of the y in the x=a having a / in it? Based on the example data above, here is where I would like to get to: cleaneddata = [ { 'x' : 'b', 'y' : '1' }, { 'x' : 'b', 'y' : '1' }, { 'x' : 'b', 'y' : '1' }, ]

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  • Can I override a query in DJango?

    - by stinkypyper
    I know you can override delete and save methods in DJango models, but can you override a select query somehow to intercept and change a parameter slightly. I have a hashed value I want to check for, and would like to keep the hashing internal to the model.

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  • nested list comprehension using intermediate result

    - by KentH
    I am trying to grok the output of a function which doesn't have the courtesy of setting a result code. I can tell it failed by the "error:" string which is mixed into the stderr stream, often in the middle of a different conversion status message. I have the following list comprehension which works, but scans for the "error:" string twice. Since it is only rescanning the actual error lines, it works fine, but it annoys me I can't figure out how to use a single scan. Here's the working code: errors = [e[e.find('error:'):] for e in err.splitlines() if 'error:' in e] The obvious (and wrong) way to simplify is to save the "find" result errors = [e[i:] for i in e.find('error:') if i != -1 for e in err.splitlines()] However, I get "UnboundLocalError: local variable 'e' referenced before assignment". Blindly reversing the 'for's in the comprehension also fails. How is this done? THanks. Kent

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  • how am I supposed to call the function?

    - by user1816768
    I wrote a program which tells you knight's movement (chess). For example if I wanted to know all possible moves, I'd input: possibilites("F4") and I'd get ['D3', 'D5', 'E2', 'E6', 'G2', 'G6', 'H3', 'H5'] as a result, ok I did that, next, I had to write a function in which you input two fields and if those fields are legal, you'd get True and if they're not you'd get False(I had to use the previous function). For example: legal("F4","D3") >>>True code: def legal(field1,field2): c=possibilities(field1) if field1 and field2 in a: return True return False I'm having a problem with the following function which I have to write: I have to put in path of the knight and my function has to tell me if it's legal path, I'm obliged to use the previous function. for example: >>> legal_way(["F3", "E1", "G2", "H4", "F5"]) True >>> legal_way(["F3", "E1", "G3", "H5"]) False >>> legal_way(["B4"]) True I know I have to loop through the list and put first and second item on it in legal(field1,field2) and if it's false, everything is false, but if it's true I have to continue to the end, and this has to work also if I have only one field. I'm stuck, what to do? def legal_way(way): a=len(way) for i in range(0,a-2): if a==1: return true else if legal(way[i],way[i+1]: return True return False and I get True or index out of range

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  • List filtering: list comprehension vs. lambda + filter

    - by Agos
    I happened to find myself having a basic filtering need: I have a list and I have to filter it by an attribute of the items. My code looked like this: list = [i for i in list if i.attribute == value] But then i thought, wouldn't it be better to write it like this? filter(lambda x: x.attribute == value, list) It's more readable, and if needed for performance the lambda could be taken out to gain something. Question is: are there any caveats in using the second way? Any performance difference? Am I missing the Pythonic Way™ entirely and should do it in yet another way (such as using itemgetter instead of the lambda)? Thanks in advance

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  • Aggregation over a few models - Django

    - by RadiantHex
    Hi folks, I'm trying to compute the average of a field over various subsets of a queryset. Player.objects.order_by('-score').filter(sex='male').aggregate(Avg('level')) This works perfectly! But... if I try to compute it for the top 50 players it does not work. Player.objects.order_by('-score').filter(sex='male')[:50].aggregate(Avg('level')) This last one returns the exact same result as the query above it, which is wrong. What am I doing wrong? Help would be very much appreciated!

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  • muti user dungeon help

    - by mudman
    ive created a single user dungeon which i would like to create into a multi user dungoen so at least two plays can play how would i do that what code do i need to add can anyone help? i would show coding but if i do then everyone would see it and all my work will be copied as i know other students do use this site to so plz understand my situation and yes this is a homework/assignment work.

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  • What is the proper way to check the previous value of a field before saving an object? (Using Django

    - by anonymous coward
    I have a Django Model with updated_by and an approved_by fields, both are ForeignKey fields to the built-in (auth) User models. I am aware that with updated_by, it's easy enough to simply over-ride the .save() method on the Model, and shove the request.user in that field before saving. However, for approved_by, this field should only ever be filled in when a related field (date_approved) is first filled in. I'm somewhat certain that I can check this logically, and fill in the field if the previous value was empty. What is the proper way to check the previous value of a field before saving an object? I do not anticipate that date_approved will ever be changed or updated, nor should there be any reason to ever update the approved_by entry. UPDATE: Regarding forms/validation, I should have mentioned that none of the fields in question are seen by or editable by users of the site. If I have misunderstood, I'm sorry, but I'm not sure how forms and validation apply to my question.

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  • How can I retrieve all the returned variables from a function?

    - by user1447941
    import random def some_function(): example = random.randint(0, 1) if example == 1: other_example = 2 else: return False return example, other_example With this example, there is a chance that either one or two variables will be returned. Usually, for one variable I'd use var = some_function() while for two, var, var2 = some_function(). How can I tell how many variables are being returned by the function?

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  • Creating tables with pylons and SQLAlchemy

    - by Sid
    I'm using SQLAlchemy and I can create tables that I have defined in /model/__init__.py but I have defined my classes, tables and their mappings in other files found in the /model directory. For example I have a profile class and a profile table which are defined and mapped in /model/profile.py To create the tables I run: paster setup-app development.ini But my problem is that the tables that I have defined in /model/__init__.py are created properly but the table definitions found in /model/profile.py are not created. How can I execute the table definitions found in the /model/profile.py so that all my tables can be created? Thanks for the help!

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