Python list to bitwise operations

Question

Is there a way to take a list of django query expresses (e.g. Q(first_name="Jordan"), where Q is django.db.models.Q) and bitwise OR them together?

In other words, I have something like this:

search_string = "various search terms"

And I want to do this:

search_params = [Q(description__icontains=term) for term in re.split(r'\W', search_string)]
search_params = something_magical(search_params)
results = Record.objects.filter(search_params)

where search_params now is equivalent to Q(description__icontains="various") | Q(description__icontains="search" | Q(description__icontains="terms"

I know it would be possible with a function like this:

def something_magical(lst):
    result = lst[0]
    for l in lst[1:]
        result |= l
    return result

So I'm wondering if this functionality is already built into Python (and I'm assuming it's more optimized than my function here).

Although I'm interested in it for this application, I'm also just interested in it theoretically.

I don't think there is such an django operator...But you could just do all the "or" queries and then use python set operators to combine the results ? ( docs.python.org/library/sets.html#set-objects ) — Richard Green
– Richard Green, Commented Jan 17, 2012 at 23:44

Mike Covington · Accepted Answer · 2015-07-01 07:14:57Z

19

You probably want

import operator 
from functools import reduce    # Python 3
search_params = reduce(operator.or_, search_params, Q())

This will place a bit-wise or (|) between all the items in search_params, starting with an empty condition Q().

edited Jul 1, 2015 at 7:14

Mike Covington

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answered Jan 17, 2012 at 23:52

Jan Pöschko

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4 Comments

Josh Smeaton Over a year ago

Nice! Things like this make my love python more and more.

Jordan Reiter Over a year ago

Just spent a little while playing with reduce and map.

Jan Pöschko Over a year ago

Great you like it! You'll probably also enjoy itertools then.

Johnston Over a year ago

Very smart. Did not know about operators as functions.

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