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How do you check if a key exists or not in a dictionary? You can check if a key exists or not in a dictionary using if-in statement/in operator, get(), keys(), handling 'KeyError' exception, and in versions older than Python 3, using has_key(). 2.
Syntax: public bool ContainsKey (TKey key); Here, the key is the Key which is to be located in the Dictionary. Return Value: This method will return true if the Dictionary contains an element with the specified key otherwise, it returns false.
You can check if a key exists in a dictionary using the keys() method and IN operator. The keys() method will return a list of keys available in the dictionary and IF , IN statement will check if the passed key is available in the list. If the key exists, it returns True else, it returns False .
On the one hand, throwing exceptions is inherently expensive, because the stack has to be unwound etc.
On the other hand, accessing a value in a dictionary by its key is cheap, because it's a fast, O(1) operation.
BTW: The correct way to do this is to use TryGetValue
obj item;
if(!dict.TryGetValue(name, out item))
return null;
return item;
This accesses the dictionary only once instead of twice.
If you really want to just return null if the key doesn't exist, the above code can be simplified further:
obj item;
dict.TryGetValue(name, out item);
return item;
This works, because TryGetValue sets item to null if no key with name exists.
Dictionaries are specifically designed to do super fast key lookups. They are implemented as hashtables and the more entries the faster they are relative to other methods. Using the exception engine is only supposed to be done when your method has failed to do what you designed it to do because it is a large set of object that give you a lot of functionality for handling errors. I built an entire library class once with everything surrounded by try catch blocks once and was appalled to see the debug output which contained a seperate line for every single one of over 600 exceptions!
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