Comparing lists of dictionaries

Question

I have two lists of test results. The test results are represented as dictionaries:

list1 = [{testclass='classname', testname='testname', testtime='...},...]
list2 = [{testclass='classname', testname='testname', ...},...]

The dictionary representation is slightly different in both lists, because for one list I have some more information. But in all cases, every test dictionary in either list will have a classname and testname element which together effectively form a way of uniquely identifying the test and a way to compare it across lists.

I need to figure out all the tests that are in list1 but not in list2, as these represent new test failures.

To do this I do:

def get_new_failures(list1, list2):
    new_failures = []
    for test1 in list1:
        for test2 in list2:
            if test1['classname'] == test2['classname'] and \
                    test1['testname'] == test2['testname']:
                break; # Not new breakout of inner loop
        # Doesn't match anything must be new
        new_failures.append(test1);
    return new_failures;

I am wondering is a more python way of doing this. I looked at filters. The function the filter uses would need to get a handle to both lists. One is easy, but I am not sure how it would get a handle to both. I do know the contents of the lists until runtime.

Any help would be appreciated,

Thanks.

Answer 1

Try this:

def get_new_failures(list1, list2):
    check = set([(d['classname'], d['testname']) for d in list2])
    return [d for d in list1 if (d['classname'], d['testname']) not in check]