比较字典列表

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]

Answer 2

If each combination of classname and testname is truly unique, then the more computationally efficient approach would be to use two dictionaries instead of two lists. As key to the dictionary, use a tuple like so: (classname, testname) . Then you can simply say if (classname, testname) in d: ... .

If you need to preserve insertion order, and are using Python 2.7 or above, you could use an OrderedDict from the collections module.

The code would look something like this:

tests1 = {('classname', 'testname'):{'testclass':'classname', 
                                     'testname':'testname',...}, 
         ...}
tests2 = {('classname', 'testname'):{'testclass':'classname', 
                                     'testname':'testname',...}, 
         ...}

new_failures = [t for t in tests1 if t not in tests2]

If you must use lists for some reason, you could iterate over list2 to generate a set, and then test for membership in that set:

test1_tuples = ((d['classname'], d['testname']) for d in test1)
test2_tuples = set((d['classname'], d['testname']) for d in test2)
new_failures = [t for t in test1_tuples if t not in test2_tuples]

Answer 3

To compare two dict d1 and d2 on a subset of their keys, use:

all(d1[k] == d2[k] for k in ('testclass', 'testname'))

And if your two list have the same lenght, you can use zip() to pair them.