How do I construct a Django reverse/url using query args?

Building an url with query string by string concatenation as suggested by some answers is as bad idea as building SQL queries by string concatenation. It is complicated, unelegant and especially dangerous with a user provided (untrusted) input. Unfortunately Django does not offer an easy possibility to pass query parameters to the reverse function.

Python standard urllib however provides the desired query string encoding functionality.

In my application I've created a helper function:

def url_with_querystring(path, **kwargs):
    return path + '?' + urllib.urlencode(kwargs) # for Python 3, use urllib.parse.urlencode instead

Then I call it in the view as follows:

quick_add_order_url = url_with_querystring(reverse(order_add),
    responsible=employee.id, scheduled_for=datetime.date.today(),
    subject='hello world!')
# http://localhost/myapp/order/add/?responsible=5&
#     scheduled_for=2011-03-17&subject=hello+world%21

Please note the proper encoding of special characters like space and exclamation mark!

I recommend to use builtin django's QueryDict. It also handles lists properly. End automatically escapes some special characters (like =, ?, /, '#'):

from django.http import QueryDict
from django.core.urlresolvers import reverse

q = QueryDict('', mutable=True)
q['some_key'] = 'some_value'
q.setlist('some_list', [1,2,3])
'%s?%s' % (reverse('some_view_name'), q.urlencode())
# '/some_url/?some_list=1&some_list=2&some_list=3&some_key=some_value'

q.appendlist('some_list', 4)
q['value_with_special_chars'] = 'hello=w#rld?'
'%s?%s' % (reverse('some_view_name'), q.urlencode())
# '/some_url/?value_with_special_chars=hello%3Dw%23rld%3F&some_list=1&some_list=2&some_list=3&some_list=4&some_key=some_value'

To use this in templates you will need to create custom template tag

Your regular expresion has no place holders (that's why you are getting NoReverseMatch):

url(r'^depict$', cyclops.django.depict, name="cyclops-depict"),

You could do it like this:

{% url cyclops-depict %}?smiles=CO&width=200&height=200

URLconf search does not include GET or POST parameters

Or if you wish to use {% url %} tag you should restructure your url pattern to something like

r'^depict/(?P<width>\d+)/(?P<height>\d+)/(?P<smiles>\w+)$' 

then you could do something like

{% url cyclops-depict 200 200 "CO" %}

---

Follow-up:

Simple example for custom tag:

from django.core.urlresolvers import reverse
from django import template
register = template.Library()

@register.tag(name="myurl")
def myurl(parser, token):
    tokens = token.split_contents()
    return MyUrlNode(tokens[1:])

class MyUrlNode(template.Node):
    def __init__(self, tokens):
        self.tokens = tokens
    def render(self, context):
        url = reverse('cyclops-depict')
        qs = '&'.join([t for t in self.tokens])
        return '?'.join((url,qs))

You could use this tag in your templates like so:

{% myurl width=200 height=200 name=SomeName %}

and hopefully it should output something like

/depict?width=200&height=200&name=SomeName