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

Django models.FileField is very helpful in simplifying file management, but sometimes you need to write/overwrite into a file field object in a view without having the admin helper functions available. It's not inherently clear how to do this manually. Never fear though it's still an easy process.

It's worth noting that Django uses a custom File class that acts as a wrapper around the python file object to add some enhanced functionality. You simply need to initialize a Django File with a python file to get a valid model.

Say you have something similar to the following model:

class FileExample(models.Model):
    test = models.FileField(upload_to='uploads')

You can then write something like this in your view:

from django.core.files import File
from test.models import FileExample

file_example = FileExample()

filename = '/path/to/file.txt'
f = open(filename, 'r')
djangofile = File(f)
file_example.test.save('filename.txt', djangofile)
f.close()

Furthermore you can combine some statements to simplify and shorten the process:

file_example = FileExample()
file_example.test.save('filename.txt', File(open('/path/to/file.txt', 'r')))

I always have to look this up, so I'm placing this here. This exports a table into a csv file in PostgreSQL.

COPY (SELECT * FROM table) TO `/path/to/file.csv` WITH CSV HEADER;

So sometimes I have an input field in a form that I want to upload files to but I want to upload multiple files at a time. I'll usually just use javascript to add and remove the field dynamically, and to keep things simple I'll keep the input name the same. I'll eventually end up with markup that looks similar to the following:

<input type="file" name="file" />
<input type="file" name="file" />
<input type="file" name="file" />

Django attaches the uploads in the FILE dictionary variable on the request object which you can access like so:

for uploaded_file in request.FILES['file']:
    # process the file

which could look something like:

# views.py
from django.http import HttpResponseRedirect

def upload_file(request):
    for uploaded_file in request.FILES.getlist('file'):
        handle_uploaded_file(uploaded_file)

    return HttpResponseRedirect(...)


def handle_uploaded_file(f):
    destination = open('/upload/path/%s' % f.name, 'wb+')

    for chunk in f.chunks():
        destination.write(chunk)
    destination.close()

Lets say I have two models connected by a OneToOne field like so:

class Post(models.Model):
    ...


class MagicalPost(models.Model):
    post = models.OneToOneField('Post')
    pony = models.TextField(max_length=100, help_text='This is where the MAGIC happens!')

I want to run a query over all MagicalPost objects but I only want to receive the Post instances.

I can use the select_related() option which will only create one database call:

magical_posts = MagicalPost.objects.select_related('post')
posts = []

for magical_post in magical_posts:
    posts.append(magical_post.post)

return posts

Or I could use two queries which syntactically is simpler:

posts_ids = MagicalPost.objects.values_list('post', flat=True)
posts = Post.objects.filter(id__in=posts_ids)
return posts

import os


directory = 'path/to/folder'

if not os.path.exists(directory):
    os.makedirs(directory)

To run a string use `exec`

code = 'print "Hello World"'
exec code

If you need to pull a value from an expression use `eval`

foo = eval('1+1')

It's not always clear how to delete a remote branch in git, but it's just the following command:

git push REMOTENAME :BRANCHNAME

 The syntax is a little wonky if you're not used to the advanced push syntax. If you look at the details of what's happening you're telling git to push nothing into the remote branch.

git push REMOTENAME LOCALBRANCHNAME:REMOTEBRANCHNAME