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# https://stackoverflow.com/questions/4916851/django-get-a-queryset-from-array-of-ids-in-specific-order/37648265#37648265

from django.db.models import Case, When

pk_list = [10, 2, 1]
preserved = Case(*[When(pk=pk, then=pos) for pos, pk in enumerate(pk_list)])
queryset = MyModel.objects.filter(pk__in=pk_list).order_by(preserved)


# pre django 1.8:

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from itertools import islice, chain

class QuerySetChain(object):
    """
    Chains multiple subquerysets (possibly of different models) and behaves as
    one queryset.  Supports minimal methods needed for use with
    django.core.paginator.

    http://stackoverflow.com/questions/431628/how-to-combine-2-or-more-querysets-in-a-django-view#answer-432666
    """

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from django.db.models import Count

def duplicates_by(model, field):
    values = model.objects\
        .values(field)\
        .annotate(Count(field))\
        .order_by(field)\
        .filter(**{'%s__count__gt' % field: 1})\
        .values_list(field, flat=True)

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gitk --first-parent --no-merges

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from datetime import timedelta
def daterange(start_date, end_date):
    for n in range(1 + int((end_date - start_date).days)):
        yield start_date + timedelta(n)

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# might need to set olcSizeLimit: 10000
ldapsearch -x -h localhost -b dc=domain,dc=org,dc=uk mail | grep '^mail:'|sort|uniq -c|sort -n|awk '$1 > 1 { print }'

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cat file | python -mjson.tool

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import subprocess
from django.core.mail import mail_admins

def convert_to_rgb(local_file):
    """
    Returns an RGB Wand image or one with the original colourspace if the conversion fails.
    Colourspace conversion is currently not working with the Wand API: https://github.com/dahlia/wand/issues/110
    """
    in_filename = '%s[0]' % local_file.name
    out_filename = '%s_rgb.jpg' % local_file.name

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lsof -Pnl +M -i4|grep :80

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fab pull_data_from_production --gateway user@mygateway.com
# first it might ask for a password for the root user but that is actually for user@mygateway.com
# then press Ctrl+D to continue if it opens an interactive ssh session on the production server
# alternatively use env.gateway = 'user@mygateway.com'