Ultramemcache: python-ultramemcached and django-ultramemached-cache

A few months ago I came across a package on GitHub called Ultramemcache, which was described as “Ultra fast memcache client written in highly optimized C++ with Python bindings.”

Using Ulramemcache, I modified the common python-memcached library to use Ultramemcache, making sure it could be used as a drop in replacement. Check out python-ultramemcached on my GitHub page.

I also put together a django cache backend using Ultramemcache. This currently does not require my python-ultramemcached library. Check out django-ultramemcached-cache on my GitHub page.

Django runserver and gevent; NotImplementedError: gevent is only usable from a single thread

Hey. So I ran into a problem when using Django runserver and Requests for Python. Specifically, when running runserver, I came across the error:

NotImplementedError: gevent is only usable from a single thread

To fix this, you need to run the gevent monkey patch in your projects manage.py.

Add the following lines in the __main__ of your manage.py

from gevent import monkey
monkey.patch_all()

Your main will look as follows:

if __name__ == "__main__":
    import gevent
    from gevent import monkey
    monkey.patch_all()
    execute_manager(settings)

phpFlickr 3.1 cache unserialize error

I came across a problem today with phpFlickr 3.1 and the way it handles its database caching. I believe it has to do with commas in the serialized data that is being inserted into the cache table. After grabbing the cache result php gave me this error in the phpFlickr library:

Notice: unserialize(): Error at offset ... phpFlickr.php

To fix this error you need to base64 encode and decode the data going into the database.

in phpFlickr modify line 144 to decode the response:

return base64_decode($result['response']);

line 177 on cache row update:

$sql = "UPDATE " . $this->cache_table . " SET response = '" . str_replace("'", "''", base64_encode($response)) . "', expiration = '" . strftime("%Y-%m-%d %H:%M:%S") . "' WHERE request = '" . $reqhash . "'";

line 180 on cache row insert:

$sql = "INSERT INTO " . $this->cache_table . " (request, response, expiration) VALUES ('$reqhash', '" . str_replace("'", "''", base64_encode($response)) . "', '" . strftime("%Y-%m-%d %H:%M:%S") . "')";

Thanks to David Walsh for his php serialize tips:
http://davidwalsh.name/php-serialize-unserialize-issues

Django AuthenticationForm and non field errors

Here’s a quick tip for the built in Django AuthenticationForm in django.contrib.auth.forms: use the non_field_errors method when trying to display the incorrect user/pass error. The error is raised in the general clean method and is not bound to any field, so using form.errors doesn’t give you the error message itself.

{{ form.non_field_errors }}

Django forms: Adding a blank option to a required choice field

Recently I came across a problem where I had a django form choicefield that needed to be required, but also needed a blank choice in case the user didn’t see the field and incorrectly submitted the first value. I saw a stack overflow post recommending to make a clean method to check that the first choice isn’t selected. That post is here:

http://stackoverflow.com/questions/5289491/blank-option-in-required-choicefield

… but a better way to do this is to simply leave the value of the blank choice as an empty string, which will invalidate the form without any extra clean method, like below:


CHOICES_WITH_BLANK = (
    ('', '--------'),
    ('1', 'choice one'),
    ('2', 'choice two'),
)

class ChoiceForm(forms.Form):
     choice_field = forms.ChoiceField(choices=CHOICES_WITH_BLANK)

Django forms: passing variables to a modelchoicefield

So I came across the problem of needing to filter my Django ModelChoiceField queryset by a variable in my view. Specifically I needed to pass the current selected state to the ModelChoiceField queryset. The best way I found to do this is to initialize the form with my state var in the initial:

state = 'OH'
form = LocationForm(initial={'state':state})

After that, instead of creating the field the traditional way, you can append the field to the self.fields dictionary within the init, enabling you to pass the initial state variable into the queryset of the field. Here is my form:

class LocationForm(forms.Form):

    def __init__(self, *args, **kwargs):
        super(LocationForm, self).__init__(*args, **kwargs)
        self.fields.insert(len(self.fields)-1, 'location',
                           forms.ModelChoiceField(queryset=Location.objects.filter(state=self.initial['state'])))

    first_name = forms.CharField(50, label="First Name")
    last_name = forms.CharField(50, label="Last Name")
    address = forms.CharField(60, label="Street Address")
    city = forms.CharField(40, label="City")
    state = USStateField()
    zip = USZipCodeField()

Self.fields is a Django SortedDict, and it’s insert method takes the index to insert to, the key, and the value.