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问题 I\'ve got a class: class ThisClass { private string a {get; set;} private string b {get; set;} } I would like to use the Intersect and Except methods of Linq, i.e.: private List<ThisClass> foo = new List<ThisClass>(); private List<ThisClass> bar = new List<ThisClass>(); Then I fill the two lists separately. I\'d like to do, for example (and I know this isn\'t right, just pseudo code), the following: foo[a].Intersect(bar[a]); How would I do this? 回答1: Maybe // returns list of intersecting

问题 Is this the right way to use the python \"with\" statement in combination with a try-except block?: try: with open(\"file\", \"r\") as f: line = f.readline() except IOError: <whatever> If it is, then considering the old way of doing things: try: f = open(\"file\", \"r\") line = f.readline() except IOError: <whatever> finally: f.close() Is the primary benefit of the \"with\" statement here that we can get rid of three lines of code? It doesn\'t seem that compelling to me for this use case

问题 List1 contains items { A, B } and List2 contains items { A, B, C } . What I need is to be returned { C } when I use Except Linq extension. Instead I get returned { A, B } and if I flip the lists around in my expression the result is { A, B, C } . Am I misunderstanding the point of Except? Is there another extension I am not seeing to use? I have looked through and tried a number of different posts on this matter with no success thus far. var except = List1.Except(List2); //This is the line I

问题 I have a nested dictionary. Is there only one way to get values out safely? try: example_dict[\'key1\'][\'key2\'] except KeyError: pass Or maybe python has a method like get() for nested dictionary ? 回答1: You could use get twice: example_dict.get('key1', {}).get('key2') This will return None if either key1 or key2 does not exist. Note that this could still raise an AttributeError if example_dict['key1'] exists but is not a dict (or a dict-like object with a get method). The try..except code

问题 This query works: mysql> SELECT s.sno FROM students s; +------+ | sno | +------+ | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | | 7 | | 8 | | 9 | | 10 | +------+ 10 rows in set (0.00 sec) This query also works: mysql> SELECT t.sno FROM take t WHERE t.cno = \'CS112\'; +------+ | sno | +------+ | 1 | | 2 | | 3 | | 4 | +------+ 4 rows in set (0.00 sec) BUT this query: SELECT s.sno FROM students s EXCEPT SELECT t.sno FROM take t WHERE t.cno = \'CS112\'; fails with the error: mysql> SELECT s.sno FROM