Sometimes you need to get at the raw value of a field in a django form. This is easily done in 1.3 using the following:

{{ form.field_name.value }}

If you're running a version lower than 1.3 you can get at the value with:

{% if form.instance.field_name %}
{{ form.instance.field_name }}
{% else %}
{{ form.data.field_name }}
{% endif %}

When overriding the change_form.html template sometimes I need access to the object that is being edited. The change_view method provides the original object in the 'original' context variable.

You can access the object in the template using the original variable:

{{ original }}

It doesn't happen a lot, but sometimes a CD or DVD gets stuck in my mac and it won't eject using the keyboard or dragging it into the trashcan.

When this happens I just open the terminal and type the following command, which usually overrides whatever is blocking the disc to eject:

drutil tray eject

Although I'm not sure when I'd ever use it there's also a close command.

drutil tray close

So if you're using virtualenv 1.7 and are wondering why you can no loger see your global Python site-packages directory it's because the default behavior has changed.

Now the default install for virtualenv is to hide site packages; equivalent to passing the old --no-site-packages command:

virtualenv --no-site-packages <env>

Since this option is now default it's no longer needed, and the new command to see the global site packages is --system-site-packages:

vitualenv --system-site-packages <env>

Hopefully this saves you some confusion as it's not clear what's happening when your new install now suddenly is breaking.

To create a random integer within a range you can use the following command:

import random

# random integer between 1 and 100
RANDOM_INTEGER = random.randint(1, 100)

Sometimes I re-key or move the domain of a server and need to reset the key so RSA doesn't complain. Technically you can just open ~/.ssh/known_hosts file and remove the entry for the dns, but the names are hashed which makes the entry difficult to find.

I used to just reset the entire known_hosts file, but that's not necessary. You can remove the domain entry with the simple command:

ssh-keygen -R example.com

Next time you try to ssh you'll be prompted to add the key as if you're visiting the site the first time. I hope this helps.

say you have two models like so:

# models.py

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey("Author")

class Author(models.Model):
    name = models.CharField(max_length=100)

In this case it would be handy if we could list the author in the list_display of the book admin, but Django gives an error if we list foreign keys like so:

# admin.py

class BookAdmin(admin.ModelAdmin):
    list_display = ('title', 'author__name')

admin.register(Book, BookAdmin)

Luckily we can easily fix this by adjusting how we link into the author foreign key. We just need to add a method to the Book ModelAdmin and return the desired string.

# admin.py

class BookAdmin(admin.ModelAdmin):
    list_display = ('title', 'author_name')

    def author_name(self, instance):
        return instance.author.name

Be careful though as gratuitous additions of foreign key field can greatly increase the load time of the admin page for the list view of the model: use this judiciously.

If you're developing in Eclipse, like I am for Android, and you use version control you're going to want to ignore the default project files that are generated by Eclipse. You should update your .gitignore with the following list:

.project
.classpath
.settings/
bin/

You can create qr codes easily in Ubuntu using qrencode. You can install it like so:

sudo apt-get install qrencode

and then create the qr code with the following command:

qrencode -o /path/to/qrcode.png -s 10 'http://example.com'

the `-s` option flag is the size of dot (pixel). The default is 3.

http://www.postgresonline.com/journal/archives/40-How-do-you-rename-a-database.html

First kick the users out of the database, you can find the users with the following command.

SELECT * 
    FROM pg_stat_activity 
    WHERE datname = 'myolddbname_goes_here'

now run the following:

ALTER DATABASE myolddbname_here RENAME TO mynewdbname_here