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  • Utility that helps in file locking - expert tips wanted

    - by maix
    I've written a subclass of file that a) provides methods to conveniently lock it (using fcntl, so it only supports unix, which is however OK for me atm) and b) when reading or writing asserts that the file is appropriately locked. Now I'm not an expert at such stuff (I've just read one paper [de] about it) and would appreciate some feedback: Is it secure, are there race conditions, are there other things that could be done better … Here is the code: from fcntl import flock, LOCK_EX, LOCK_SH, LOCK_UN, LOCK_NB class LockedFile(file): """ A wrapper around `file` providing locking. Requires a shared lock to read and a exclusive lock to write. Main differences: * Additional methods: lock_ex, lock_sh, unlock * Refuse to read when not locked, refuse to write when not locked exclusivly. * mode cannot be `w` since then the file would be truncated before it could be locked. You have to lock the file yourself, it won't be done for you implicitly. Only you know what lock you need. Example usage:: def get_config(): f = LockedFile(CONFIG_FILENAME, 'r') f.lock_sh() config = parse_ini(f.read()) f.close() def set_config(key, value): f = LockedFile(CONFIG_FILENAME, 'r+') f.lock_ex() config = parse_ini(f.read()) config[key] = value f.truncate() f.write(make_ini(config)) f.close() """ def __init__(self, name, mode='r', *args, **kwargs): if 'w' in mode: raise ValueError('Cannot open file in `w` mode') super(LockedFile, self).__init__(name, mode, *args, **kwargs) self.locked = None def lock_sh(self, **kwargs): """ Acquire a shared lock on the file. If the file is already locked exclusively, do nothing. :returns: Lock status from before the call (one of 'sh', 'ex', None). :param nonblocking: Don't wait for the lock to be available. """ if self.locked == 'ex': return # would implicitly remove the exclusive lock return self._lock(LOCK_SH, **kwargs) def lock_ex(self, **kwargs): """ Acquire an exclusive lock on the file. :returns: Lock status from before the call (one of 'sh', 'ex', None). :param nonblocking: Don't wait for the lock to be available. """ return self._lock(LOCK_EX, **kwargs) def unlock(self): """ Release all locks on the file. Flushes if there was an exclusive lock. :returns: Lock status from before the call (one of 'sh', 'ex', None). """ if self.locked == 'ex': self.flush() return self._lock(LOCK_UN) def _lock(self, mode, nonblocking=False): flock(self, mode | bool(nonblocking) * LOCK_NB) before = self.locked self.locked = {LOCK_SH: 'sh', LOCK_EX: 'ex', LOCK_UN: None}[mode] return before def _assert_read_lock(self): assert self.locked, "File is not locked" def _assert_write_lock(self): assert self.locked == 'ex', "File is not locked exclusively" def read(self, *args): self._assert_read_lock() return super(LockedFile, self).read(*args) def readline(self, *args): self._assert_read_lock() return super(LockedFile, self).readline(*args) def readlines(self, *args): self._assert_read_lock() return super(LockedFile, self).readlines(*args) def xreadlines(self, *args): self._assert_read_lock() return super(LockedFile, self).xreadlines(*args) def __iter__(self): self._assert_read_lock() return super(LockedFile, self).__iter__() def next(self): self._assert_read_lock() return super(LockedFile, self).next() def write(self, *args): self._assert_write_lock() return super(LockedFile, self).write(*args) def writelines(self, *args): self._assert_write_lock() return super(LockedFile, self).writelines(*args) def flush(self): self._assert_write_lock() return super(LockedFile, self).flush() def truncate(self, *args): self._assert_write_lock() return super(LockedFile, self).truncate(*args) def close(self): self.unlock() return super(LockedFile, self).close() (the example in the docstring is also my current use case for this) Thanks for having read until down here, and possibly even answering :)

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  • Store value of os.system or os.popen

    - by chrissygormley
    Hello, I want to grep the error's out of a log file and save the value as an error. When I use: errors = os.system("cat log.txt | grep 'ERROR' | wc -l") I get the return code that the command worked or not. When I use: errors = os.popen("cat log.txt | grep 'ERROR' | wc -l") I get what the command is trying to do. When I run this in the command line I get 3 as thats how many errors there are. Can anyone suggest another way? Thanks

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  • How do i deserialize an object with pyYaml using safe_load?

    - by systempuntoout
    Having a snippet like this: import yaml class User(object): def __init__(self, name, surname): self.name= name self.surname= surname user = User('spam', 'eggs') serialized_user = yaml.dump(user) deserialized_user = yaml.load(serialized_user) print "name: %s, surname %s" % (deserialized_user.name, deserialized_user.surname) Yaml docs says that it is not safe to call yaml.load with any data received from an untrusted source; so, what do i need to modify to my snippet\class to use safe_load method? Is it possible?

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  • Proper way to set class variables

    - by ensnare
    I'm writing a class to insert users into a database, and before I get too far in, I just want to make sure that my OO approach is clean: class User(object): def setName(self,name): #Do sanity checks on name self._name = name def setPassword(self,password): #Check password length > 6 characters #Encrypt to md5 self._password = password def commit(self): #Commit to database >>u = User() >>u.setName('Jason Martinez') >>u.setPassword('linebreak') >>u.commit() Is this the right approach? Should I declare class variables up top? Should I use a _ in front of all the class variables to make them private? Thanks for helping out.

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  • Can I treat IronPython as a Pythonic replacement to C#?

    - by Ewan Nathaniel
    Hey guys! I do understand that this topic has been covered in some way at StackOverflow but I'm still not able to figure out the exact answer: can I treat IronPython as a Pythonic replacement to C#? I use CPython every day, I love the Zen :) but my current task is a Windows-only application with a complex GUI and some other features which I would like to implement using .NET.

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  • Generic function that accept a table and column name and returns all the primary key values that mat

    - by nashr rafeeg
    i have functions that look like this that is littered through out the code def get_M_status(S): M_id = merital.select(merital.c.marital_status_description == S).execute().fetchone() if M_id == None: print "Warning: No Marital id found for %s Merital status to Single" % S M_id = merital.select(merital.c.marital_status_description == "Single").execute().fetchone() return M_id[0] i was wondering if their is a way to write a generic function where i can pass the relevant values ie: table name primary key column filter column and filter value cheers

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  • How do I mock a class property with mox?

    - by Harley
    I have a class: class myclass(object): @property def myproperty(self): return 'hello' Using mox and py.test, how do I mock out myproperty? I've tried: mock.StubOutWithMock(myclass, 'myproperty') myclass.myproperty = 'goodbye' and mock.StubOutWithMock(myclass, 'myproperty') myclass.myproperty.AndReturns('goodbye') but both fail with AttributeError: can't set attribute.

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  • unittest tests reuse for family of classes

    - by zaharpopov
    I have problem organizing my unittest based class test for family of tests. For example assume I implement a "dictionary" interface, and have 5 different implementations want to testing. I do write one test class that tests a dictionary interface. But how can I nicely reuse it to test my all classes? So far I do ugly: DictType = hashtable.HashDict In top of file and then use DictType in test class. To test another class I manually change the DictType to something else. How can do this otherwise? Can't pass arguments to unittest classes so is there a nicer way?

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  • Django: Odd mark_safe behaviour?

    - by Mark
    I wrote this little function for writing out HTML tags: def html_tag(tag, content=None, close=True, attrs={}): lst = ['<',tag] for key, val in attrs.iteritems(): lst.append(' %s="%s"' % (key, escape_html(val))) if close: if content is None: lst.append(' />') else: lst.extend(['>', content, '</', tag, '>']) else: lst.append('>') return mark_safe(''.join(lst)) Which worked great, but then I read this article on efficient string concatenation (I know it doesn't really matter for this, but I wanted consistency) and decided to update my script: def html_tag(tag, body=None, close=True, attrs={}): s = StringIO() s.write('<%s'%tag) for key, val in attrs.iteritems(): s.write(' %s="%s"' % (key, escape_html(val))) if close: if body is None: s.write(' />') else: s.write('>%s</%s>' % (body, tag)) else: s.write('>') return mark_safe(s.getvalue()) But now my HTML get escaped when I try to render it from my template. Everything else is exactly the same. It works properly if I replace the last line with return mark_safe(unicode(s.getvalue())). I checked the return type of s.getvalue(). It should be a str, just like the first function, so why is this failing?? Also fails with SafeString(s.getvalue()) but succeeds with SafeUnicode(s.getvalue()). I'd also like to point out that I used return mark_safe(s.getvalue()) in a different function with no odd behavior. The "call stack" looks like this: class Input(Widget): def render(self): return html_tag('input', attrs={'type':self.itype, 'id':self.id, 'name':self.name, 'value':self.value, 'class':self.itype}) class Field: def __unicode__(self): return mark_safe(self.widget.render()) And then {{myfield}} is in the template. So it does get mark_safed'd twice, which I thought might have been the problem, but I tried removing that too..... I really have no idea what's causing this, but it's not too hard to work around, so I guess I won't fret about it.

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  • Django model: Reference foreign key table in __unicode__ function for admin

    - by pa
    Example models: class Parent(models.Model): name = models.CharField() def __unicode__(self): return self.name class Child(models.Model): parent = models.ForeignKey(Parent) def __unicode__(self): return self.parent.name # Would reference name above I'm wanting the Child.unicode to refer to Parent.name, mostly for the admin section so I don't end up with "Child object" or similar, I'd prefer to display it more like "Child of ". Is this possible? Most of what I've tried hasn't worked unfortunately.

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  • Changing models in django results in broken database?

    - by Rhubarb
    I have added and removed fields in my models.py file and then run manage.py syncdb. Usually I have to quit out of the shell and restart it before syncdb does anything. And then even after that, I am getting errors when trying to access the admin pages, it seems that certain new fields that I've added still don't show up in the model: Caught an exception while rendering: no such column: mySite_book.Title

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  • Regex to match words and those with an apostrophe

    - by Beau Martínez
    I'm looking for a regex to only match words, possibly including numbers, and possibly with an apostrophe at the beginning, middle, or end; and ignore everything else. So these would be matched verbatim: 'bout it's persons' But these would be ignored: ' '' However, for words like 'open', open should be matched.

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  • Django Class Views and Reverse Urls

    - by kalhartt
    I have a good many class based views that use reverse(name, args) to find urls and pass this to templates. However, the problem is class based views must be instantiated before urlpatterns can be defined. This means the class is instantiated while urlpatterns is empty leading to reverse throwing errors. I've been working around this by passing lambda: reverse(name, args) to my templates but surely there is a better solution. As a simple example the following fails with exception: ImproperlyConfigured at xxxx The included urlconf mysite.urls doesn't have any patterns in it mysite.urls from mysite.views import MyClassView urlpatterns = patterns('', url(r'^$' MyClassView.as_view(), name='home') ) views.py class MyClassView(View): def get(self, request): home_url = reverse('home') return render_to_response('home.html', {'home_url':home_url}, context_instance=RequestContext(request)) home.html <p><a href={{ home_url }}>Home</a></p> I'm currently working around the problem by forcing reverse to run on template rendering by changing views.py to class MyClassView(View): def get(self, request): home_url = lambda: reverse('home') return render_to_response('home.html', {'home_url':home_url}, context_instance=RequestContext(request)) and it works, but this is really ugly and surely there is a better way. So is there a way to use reverse in class based views but avoid the cyclic dependency of urlpatterns requiring view requiring reverse requiring urlpatterns...

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  • Django updating db for selected ids

    - by Hulk
    In the following, New row values in DB are 6,8.They are the ids of a field I want to update these some other fields in the table based on these values row_newid=request.POST.get('row_updated_id') //Array row_newdata=request.POST.get('row_updated_data') //Array for newrow in row_newid: //how to update row_newdata for newrow values No for all the ids in row_newid how do i update row_newdata. row_newdata has the values 'a' and 'b' for example. thanks....

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  • Problem in adding custom fields to django-registration

    - by Pankaj Singh
    I tried extending RegistrationFormUniqueEmail class CustomRegistrationFormUniqueEmail(RegistrationFormUniqueEmail): first_name = forms.CharField(label=_('First name'), max_length=30,required=True) last_name = forms.CharField(label=_('Last name'), max_length=30, required=True) def save(self, profile_callback=None): new_user = super(CustomRegistrationFormUniqueEmail, self).save(profile_callback=profile_callback) new_user.first_name = self.cleaned_data['first_name'] new_user.last_name = self.cleaned_data['last_name'] return new_user then changing view # form = form_class(data=request.POST, files=request.FILES) form = CustomRegistrationFormUniqueEmail(data=request.POST, files=request.FILES) but still I am seeing default view containg four fields only .. help is needed

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  • Django aggregation query on related one-to-many objects

    - by parxier
    Here is my simplified model: class Item(models.Model): pass class TrackingPoint(models.Model): item = models.ForeignKey(Item) created = models.DateField() data = models.IntegerField() In many parts of my application I need to retrieve a set of Item's and annotate each item with data field from latest TrackingPoint from each item ordered by created field. For example, instance i1 of class Item has 3 TrackingPoint's: tp1 = TrackingPoint(item=i1, created=date(2010,5,15), data=23) tp2 = TrackingPoint(item=i1, created=date(2010,5,14), data=21) tp3 = TrackingPoint(item=i1, created=date(2010,5,12), data=120) I need a query to retrieve i1 instance annotated with tp1.data field value as tp1 is the latest tracking point ordered by created field. That query should also return Item's that don't have any TrackingPoint's at all. If possible I prefer not to use QuerySet's extra method to do this. That's what I tried so far... and failed :( Item.objects.annotate(max_created=Max('trackingpoint__created'), data=Avg('trackingpoint__data')).filter(trackingpoint__created=F('max_created')) Any ideas?

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  • Is it possible to change the model name in the django admin site?

    - by luc
    Hello, I am translating a django app and I would like to translate also the homepage of the django admin site. On this page are listed the application names and the model class names. I would like to translate the model class name but I don't find how to give a user-friendly name for a model class. Does anybody know how to do that?

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  • How to create a UserProfile form in Django with first_name, last_name modifications ?

    - by Natim
    If think my question is pretty obvious and almost every developer working with UserProfile should be able to answer it. However, I could not find any help on the django documentation or in the Django Book. When you want to do a UserProfile form in with Django Forms, you'd like to modify the profile fields as well as some User field. But there is no forms.UserProfileForm (yet?) ! How do you do that ?

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  • slicing behaviour question of a list of lists

    - by Lex
    I got a function like def f(): ... ... return [list1, list2] this returns a list of lists [[list1.item1,list1.item2,...],[list2.item1,list2.item2,...]] now when I do the following: for i in range(0,2):print f()[i][0:10] it works and print the lists sliced but if i do print f()[0:2][0:10] then it prints the lists ignoring the [0:10] slicing. Is there any way to make the second form work or do I have to loop every time to get the desired result?

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  • Matching 3 out 5 fields - Django

    - by RadiantHex
    Hi folks, I'm finding this a bit tricky! Maybe someone can help me on this one I have the following model: class Unicorn(models.Model): horn_length = models.IntegerField() skin_color = models.CharField() average_speed = models.IntegerField() magical = models.BooleanField() affinity = models.CharField() I would like to search for all similar unicorns having at least 3 fields in common. Is it too tricky? Or is it doable?

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  • Getting "Comment post not allowed (400)" when using Django Comments

    - by kfordham281
    I'm going through a Django book and I seem to be stuck. The code base used in the book is .96 and I'm using 1.0 for my Django install. The portion I'm stuck at is related to Django comments (django.contrib.comments). When I submit my comments I get "Comment post not allowed (400) Why: Missing content_type or object_pk field". I've found the Django documentation to be a bit lacking in this area and I'm hoping to get some help. The comment box is displayed just fine, it's when I submit the comment that I get the above error (or security warning as it truly appears). My call to the comment form: {% render_comment_form for bookmarks.sharedbookmark shared_bookmark.id %} My form.html code: {% if user.is_authenticated %} <form action="/comments/post/" method="post"> <p><label>Post a comment:</label><br /> <textarea name="comment" rows="10" cols="60"></textarea></p> <input type="hidden" name="options" value="{{ options }}" /> <input type="hidden" name="target" value="{{ target }}" /> <input type="hidden" name="gonzo" value="{{ hash }}" /> <input type="submit" name="post" value="submit comment" /> </form> {% else %} <p>Please <a href="/login/">log in</a> to post comments.</p> {% endif %} Any help would be much appreciated. My view as requested: def bookmark_page(request, bookmark_id): shared_bookmark = get_object_or_404( SharedBookmark, id=bookmark_id ) variables = RequestContext(request, { 'shared_bookmark': shared_bookmark }) return render_to_response('bookmark_page.html', variables)

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  • RFC regarding WAM

    - by Noctis Skytower
    Request For Comment regarding Whitespace's Assembly Mnemonics What follows in a first generation attempt at creating mnemonics for a whitespace assembly language. STACK ===== push number copy copy number swap away away number MATH ==== add sub mul div mod HEAP ==== set get FLOW ==== part label call label goto label zero label less label back exit I/O === ochr oint ichr iint In the interest of making improvements to this small and simple instruction set, this is a second attempt. hold N Push the number onto the stack copy Duplicate the top item on the stack copy N Copy the nth item on the stack (given by the argument) onto the top of the stack swap Swap the top two items on the stack drop Discard the top item on the stack drop N Slide n items off the stack, keeping the top item add Addition sub Subtraction mul Multiplication div Integer Division mod Modulo save Store load Retrieve L: Mark a location in the program call L Call a subroutine goto L Jump unconditionally to a label if=0 L Jump to a label if the top of the stack is zero if<0 L Jump to a label if the top of the stack is negative return End a subroutine and transfer control back to the caller exit End the program print chr Output the character at the top of the stack print int Output the number at the top of the stack input chr Read a character and place it in the location given by the top of the stack input int Read a number and place it in the location given by the top of the stack What do you think of the following revised list for Whitespace's assembly instructions? I'm still thinking outside of the box somewhat and trying to come up with a better mnemonic set than last time. When the previous interpreter was written, it was completed over two contiguous, rushed evenings. This rewrite deserves significantly more time now that it is the summer. Of course, the next version of Whitespace (0.4) may have its instructions revised even more, but this is just a redesign of what originally was done in a very short amount of time. Hopefully, the instructions make more sense once someone new to programmings thinks about them.

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  • Create matplotlib legend out of the figure

    - by Werner
    I added the legend this way: leg = fig.legend((l0,l1,l2,l3,l4,l5,l6), ('0 Cl : r2, slope, origin', '1 Cl :'+str(r1b)+' , '+str(m1)+' , '+str(b1), '2 Cl :'+str(r2b)+' , '+str(m2)+' , '+str(b2), '3 Cl :'+str(r3b)+' , '+str(m3)+' , '+str(b3), '4 Cl :'+str(r4b)+' , '+str(m4)+' , '+str(b4), '5 Cl :'+str(r5b)+' , '+str(m5)+' , '+str(b5), '6 Cl :'+str(r6b)+' , '+str(m6)+' , '+str(b6), ), 'upper right') but the legend appears inside the plot. How can I tell matplotlib to put it to the right of the plot and at the right?

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