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Dictionary derivation (Dictionary comprehensions) and set derivation (Set comprehensions)

Most Python programmers know and have used list derivation (list comprehensions). If you are not familiar with the concept of list comprehensions-a list comprehension is a shorter, concise way to create a list.

> some_list = [1,2,3,4,5] > > another_list = [x + 1 for x in some_list] > another_list [2,3,4,5,6]

Since python 3. 1 (or even Python 2. 7), we can use the same syntax to create collections and dictionary tables:

> > # Set Comprehensions > some_list = [1, 2, 3, 4, 5, 2, 5, 1, 4, 8] > > even_set = {x for x in some_list if x% 2 = = 0} > even_setset ([8,2,4]) > # Dict Comprehensions > d = {x: X% 2 = = 0 for x in range (1,11)} > > d {1: False, 2: True, 3: False, 4: True, 5: False, 6: True, 7: False, 8: True, 9: False, 10: True}

In the first example, we create a set with non-repeating elements based on some_list, and the set contains only even numbers. In the example of the dictionary table, we create an integer between 1 and 10 that key is not repeated, and value is Boolean to indicate whether key is even.

Another thing worth noting here is the literal representation of the set. We can simply create a collection in this way:

> my_set = {1,2,2,3,4} > my_setset ([1,2,3,4])

Instead of using the built-in function set ().

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