If you've ever wanted to dynamically lookup values in the template layer (e.g. dictionary[bar]), then you've probably realized/been told to do this in the python layer. The problem is then you often to build a huge 2-D list to hold all of that data.
These are two solutions to this problem: by using generators we can be lazy while still making it easy in the python layer. I'm going to write more documentation later, but here's a quick example:
from lazy_lookup import lazy_lookup_dict
def some_view(request):
users = User.objects.values('id', 'username')
articles = Article.objects.values('user', 'title', 'body')
articles = dict([(x['user'], x) for x in articles])
return render_to_response('some_template.html',
{'data': lazy_lookup_dict(users, key=lambda x: x['id'],
article=articles,
item_name='user')})
Then in the template layer you'd write something like:
{% for user_data in data %}
{{ user_data.user.username }}, {{ user_data.article.title }}
{% endfor %}
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 | def lazy_lookup_tuple(iterable, *args, **kwargs):
""" Generates a lookup over all iterations of the iterable.
The keyword parameters are:
- key: A function which, given an item in the iterable,
returns the key upon which to lookup from the lookup
objects.
Defaults to the identity function.
- default: The value which a field defaults to if nothing
the item doesn't coorespond in the lookup.
Defaults to None.
All position arguments (excepting the first one) are objects
that support lookup via __getitem__ (e.g. a dict object).
This returns a generator which yields tuples of
the form:
(item, args[0][key(item)], args[1][key(item)], ...)
"""
default = None
key_func = lambda x: x
if 'key' in kwargs:
key_func = kwargs['key']
if 'default' in kwargs:
default = kwargs['default']
def get_item(object, key):
try:
return object[key]
except KeyError:
if callable(default):
return default(key)
else:
return default
for item in iterable:
key = key_func(item)
yield tuple([item] + map(lambda arg: get_item(arg, key), args))
def lazy_lookup_dict(iterable, *args, **kwargs):
""" Generates a lookup over all iterations of the iterable.
The keyword parameters are:
- key: A function which, given an item in the iterable,
returns the key upon which to lookup from the lookup
objects.
Defaults to the identity function.
- default: The value which a field defaults to if nothing
the item doesn't coorespond in the lookup.
Defaults to None.
- item_name: The label for the item in the dictionary that's
yielded.
Defaults to 'item'.
All keyword arguments (except the above ones) are objects
that support lookup via __getitem__ (e.g. a dict object).
This returns a generator which yields dictionaries of
the form:
{'item': item, kwarg_name1: kwarg_value1[key(item)], ...}
"""
default = None
key_func = lambda x: x
item_name = 'item'
if 'key' in kwargs:
key_func = kwargs['key']
del kwargs['key']
if 'default' in kwargs:
default = kwargs['default']
del kwargs['default']
if 'item_name' in kwargs:
item_name = kwargs['item_name']
del kwargs['item_name']
def get_item(object, key):
try:
return object[key]
except KeyError:
if callable(default):
return default(key)
else:
return default
for item in iterable:
key = key_func(item)
yield dict([(item_name, item)] +
map(lambda kwarg: (kwarg[0], get_item(kwarg[1], key)), kwargs.items()))
|
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