List comprehensions are an easy way to make a list out of another list.
For example:
list1 = [1, 2, 3, 4, 5, 6]
print(list1)
list2 = [x**2 for x in list1]
print(list2)
[1, 2, 3, 4, 5, 6][1, 4, 9, 16, 25, 36]
A similar construct exists for dictionaries and is called dictionary comprehension:
dic1 = {'Good': 4, 'Excellent': 5, 'Bad': 3}
print("Dic1 is {}".format(dic1))
dic2 = { v:k for k,v in dic1.items()}
print("Dic2 is {}".format(dic2))
Dic1 is {'Bad': 3, 'Excellent': 5, 'Good': 4} Dic2 is {3: 'Bad', 4: 'Good', 5: 'Excellent'}
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