Question

I have a really weird thing happening. I am trying to loop through a set of dictionaries to find all of the items with a specific value related to a field key. Take the following:

ex_set is an output from a mysql system that I do not have control over. If I had to re-create it using python, it would be something like:

dict_a [ 'field' ] = 'fruit'
dict_a [ 'value' ] = 'apple'
dict_b [ 'field' ] = 'fruit'
dict_b [ 'value' ] = 'berry'
ex_set = set()
ex_set.add (dict_a,dict_b)

The important thing is how the set looks when I pprint it.

pprint (ex_set)
OUTPUTS> ({'field' : 'fruit',
        'value' : 'apple'},
        'field' : 'fruit'},
        'value' : 'berry'})

i = 0
while len ( ex_set ) > i:
    for k , v in ex_set [i].iteritems ( ):
        if v == 'fruit':
        pprint ( ex_set[i] )
    i += 1

The problem is that the printing of this does not print all of the dictionaries that have a value = “fruit”.

Is there a better way to search through a set of dictionaries? The set that I am searching through has 3 key/value combinations in each dictionary and about 30k dictionaries. This works about 25% of the time and I can’t figure out why it is only returning about 20% of the matches.

Thanks for the help!

Answer 1

Based on your description you are seeking something like:

In [6]: ex_set = ({'fruit':'apple',
   ...:            'value':'fruit'},
   ...:           {'fruit':'fruit'},
   ...:           {'apple':'apple'})

In [7]: for d in ex_set:
   ...:     if 'fruit' in d.values():
   ...:         print(d)
   ...:         
{'fruit': 'apple', 'value': 'fruit'}
{'fruit': 'fruit'}

Also, in addition to the fact, that your example isn’t valid python, ex_set certainly can’t be a set, as sets's cant contain dictionaries as they are unhashable. I would consider renaming it to something more suitable:

In [8]: set([{}])
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-8-7facc835553f> in <module>()
----> 1 set([{}])

TypeError: unhashable type: 'dict'