I have two lists, one with old IDs and one with new IDs.
I want to get items in common and items not common.
The new_Items list has all new ones. The old_Items has the old ones.
I suppose that when I calculate the ones in common plus the in new items list but not in old items list, I get the actual number of new items.
Here is the code and the output.
print(old_Items)
print(new_Items)
common = set(new_Items) & set(old_Items)
not_common = set(new_Items) - set(old_Items)
print(len(old_Items))
print(len(new_Items))
print(len(common))
print(len(not_common))
output
['312064913440', '312062038159', '382373644951', '312061362147', '312063436815', '382376480677', '382376472268', '382377376960', '382377376948', '312064169607', '312064914150', '312064169620', '312064169613', '382376480674', '382376472280', '382378338388', '312061362154', '312063426996', '382377376961', '312064912982', '312064912973', '312063426974', '312063427017', '312063427025', '312063436813', '312064913415', '382378337435', '382378337746', '382378337752', '382378338374', '382378338378', '382378338385', '382378338387', '382378338389', '382378338392', '312063436814', '312064169626', '312064912968', '312064912971', '312064912972', '312064912981', '312064913414', '312064913435', '312064914151', '312064914158', '382376480665', '382378337434', '382378337437', '382378337449', '382378337456', '382378337737', '382378337757', '312063426962', '382376480681', '382376472292', '382376480675', '382377376955', '312064914146', '382378337735', '312064912964', '312064913436', '312064914160', '382376472265', '382378337443', '382378337738', '382378337740', '312063436819', '382376472311', '382376480678', '382376480667', '312063426963', '312063426969', '312063426988', '312063426991', '312063427011', '312063427027', '312063436817', '312064169618', '312064169622', '312064169623', '312064912959', '312064912966', '312064912974', '312064912975', '312064912976', '312064912979', '312064912980', '312064912985', '312064913416', '312064913417', '312064913420', '312064913424', '312064913427', '312064913437', '312064913439', '312064913442', '312064914148', '312064914155', '312064914162', '312064914163', '312064914164', '312064914166', '382376472307', '382376480658', '382376480679', '382377376950', '382378337438', '382378337442', '382378337444', '382378337445', '382378337446', '382378337448', '382378337455', '382378337458', '382378337460', '382378337739', '382378337742', '382378337745', '382378337748', '382378337749', '382378337750', '382378337756', '382378337758', '382378337759', '382378337765', '382378338361', '382378338363', '382378338372', '382378338373', '382378338377', '382378338379', '382378338382', '382378338383', '382378338384', '312062038160', '312063426970', '312063427014', '312063427022', '312063436820', '312063436821', '312063436822', '312064169625', '312064169630', '312064912962', '312064912963', '312064912969', '312064912978', '312064912983', '312064912984', '312064912986', '312064912987', '312064912988', '312064913419', '312064913425', '312064913432', '312064913438', '312064914147', '312064914154', '312064914159', '312064914161', '382376472276', '382376472282', '382376472297', '382376472308', '382376480659', '382376480663', '382376480670', '382376480673', '382376480676', '382376480684', '382376480686', '382376480687', '382377376951', '382378337433', '382378337436', '382378337439', '382378337447', '382378337450', '382378337451', '382378337452', '382378337454', '382378337457', '382378337736', '382378337741', '382378337743', '382378337747', '382378337751', '382378337754', '382378337760', '382378337761', '382378337763', '382378337764', '382378338362', '382378338365', '382378338366', '382378338367', '382378338368', '382378338369', '382378338370', '382378338371', '382378338381', '382378338386', '382378338390', '312063426985', '312064169612', '382376480671', '312063427019', '312064169608', '312064169610', '312063436828', '312064169619', '382378337755', '312062714117', '312063436833', '312064169611', '382373643627', '382376472281', '382376472287', '382376472301', '382376472302', '382376480661', '382377376952', '382377376954', '382377376956', '382377376957', '382377376959', '382378337459', '312063426973', '312063427005', '312063436826', '312064169606', '312064169624', '312064169628', '382373643615', '382376472288', '382376480666', '382376480669', '382376480682', '312063427002', '312063436831', '312064169614', '312064169615', '382376480662', '382377376947', '312063426998', '382376480664', '382376480668', '382377376958', '312063426992', '312063436810', '312064169605', '312064912970', '312064913418', '312064913429', '312064913431', '382376480660', '382378337753', '382378338364', '382378338380', '312063426964', '312063426957', '312063436809', '312063436812', '382376472298', '382378338393', '382376480680', '312064169629', '312064913423', '312064914152', '312064914157', '312064914165', '382378338375', '382378338376', '312063426977', '312063426978', '382376472279', '312063436827', '382376472275', '382377376949', '312063427001', '312063436825', '312063436829', '312063436830', '312063426989', '312063426993', '312064169609', '382375693533', '382376472267', '382376472299', '382376480685', '312063436832']
['312065926243', '382376472268', '312067111164', '382378338380', '312064913415', '382380706562', '382380706577', '382380706899', '382379331671', '382376480673', '382376480674', '312067111153', '382380706584', '382378337450', '382378337454', '382376472301', '312067111663', '382378337459', '382379835966', '382379835959', '382379835961', '382380706907', '382378337444', '382380706580', '382378337436', '312066454641', '312063426992', '312067111152', '382379335272', '382378337752', '382378337449', '382378337437', '312067111167', '312066454623', '312067111471', '382379835965', '382380706919', '312066454621', '312067111158', '312067111163', '312067111468', '312067111647', '382380706718', '382380706732', '312067111150', '312067111446', '382379331513', '382379835967', '312067111436', '312067111462', '312067111464', '312067111466', '312067111468', '312067111647', '312067111652', '382380706583', '382380706718', '382380706723', '382380706732', '382380706894', '382380706897', '382380706912', '382379331513', '382379835967', '382378337435', '312064912968', '382378337456', '312064912971', '312064912972', '312064914151', '312066454616', '312066454639', '382378338378', '312064912981', '312067111435', '382376472292', '382378337434', '312064912973', '312064914158', '312067111169', '312067111443', '312067111646', '312067111676', '382380706567', '382380706559', '382380706572', '382380706719', '312064914160', '382378337443', '312064914146', '312067111442', '312067111441', '312067111463', '382378337735', '382376472265', '312063436819', '312067111441', '382376472311', '312064914155', '312063427014', '312063436822', '312064912984', '312066454628', '312063436817', '382378337756', '382376480670', '312064912962', '312064913438', '312066454629', '312066454634', '312066454635', '312066454645', '312067111143', '312067111451', '312067111452', '312067111454', '312067111467', '312067111470', '312067111650', '312067111653', '312067111654', '312067111662', '312067111665', '312067111671', '382379835960', '382379835962', '382379835968', '382379835971', '382380706573', '382380706727', '382380706728', '382380706915', '382380706917', '382380706920', '312065919161', '312066454625', '312067111147', '312067111156', '312067111159', '312067111457', '312067111458', '312067111460', '312067111461', '312067111651', '312067111667', '312067111672', '382379835958', '382380706574', '382380706722', '382380706901', '312064913432', '382378337433', '312067111154', '312067111165', '382380706892', '382378338379', '382378338365', '312064912988', '312067111455', '312067111465', '312067111657', '312067111660', '312067111664', '382378337447', '382380706729', '312063436828', '382378338377', '312064913427', '382378337438', '312064913442', '312064912987', '382378337452', '382378338362', '382378337455', '312064912979', '312067111168', '382380706717', '312063427011', '382378337750', '382378337458', '382378337743', '382378338373', '312067111140', '382379835974', '382380706565', '382380706734', '312064912975', '382378337446', '312064914162', '382378338382', '312064914166', '312063426998', '312064914166', '312063426998', '312063427019', '382378337754', '312064912963', '382378338369', '382379835964', '382376472282', '312064914148', '312066454618', '312066454619', '312066454626', '312066454631', '312067111141', '312067111166', '312067111447', '312067111453', '312067111456', '382379835972', '382380706716', '382380706724', '382380706736', '382380706913', '312066454630', '312066454633', '312066454636', '312066454643', '312067111151', '312067111157', '312067111449', '312067111469', '312067111656', '312067111658', '312067111669', '312067111670', '312067111675', '382379835970', '382380706566', '382380706575', '382380706582', '382380706725', '382380706726', '382380706730', '382380706733', '382380706898', '382380706903', '382380706905', '382380706906', '382378338372', '312066454620', '312066454637', '312067111162', '312067111666', '382379835953', '382380706570', '382380706578', '382380706896', '382380706916', '312066454617', '312066454622', '312066454632', '312067111145', '312067111146', '382379835954', '382379835963', '382380706576', '382378337765', '312063426969', '382379835969', '382378337451', '382378338368', '382378337448', '382378337442', '382378338371', '382378337439', '382378338386', '312064912986', '382376472307', '382376480687', '312064912976', '312064912983', '382378337457', '312065916615', '382379835952', '312066454615', '312066454627', '382379835955', '382380706561', '382380706571', '382380706714', '382378338366', '382380706564', '312064912974', '382378337460', '382380706581', '382376480660', '312063427002', '312064912978', '312067111439', '382380706900', '312067111160', '382379835951', '382380706721', '382380706908', '312067111438', '312067111649', '382380706560', '382380706895', '382380706918', '382378337445', '312064912959', '312064912966', '382376480680', '312063436809', '382376472298', '382379835957', '382379835973', '312063427001', '312063426977', '382378338393', '312063426957', '312063436830', '312063436812', '312063436829', '382376472275', '312063436825', '312064913423', '382376472299', '382376472267', '312063436832', '312064914157', '382378338375', '312064914165', '382378338376', '312064914152']
291 # number of items in old_items
327 # number of items in new_items
122 # intersection result
196 # result of newitems set - olditems set
What you're looking for is called the "symmetric difference".
set(new_Items) ^ set(old_Items)
Or,
set(new_Items).symmetric_difference(old_Items)
This gives you items that belong to either set, but not both. You are currently computing only those items that belong to new_Items, but not the other way round, hence the discrepancy.
Refer to the set.symmetric_difference docs.
A-B gives items of A which are not in B B-A gives items of B which are not in A Either of these is not what you are looking for
For items not common you need (A union B) minus (A intersection B) which is the symmetric difference of sets
You can also get by "(A-B) union (B-A)"
The list had some repeated items, that was the problem.
So the set cuts these repeated items and that is why printing less numbers than I expect.
来源：https://stackoverflow.com/questions/48807504/python-intersection-and-difference-sum-doesnt-give-me-the-actual-number-of-the