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Can somebody tell me what that one line of code does? Thanks

+4 votes
asked Oct 19, 2022 by Eidnoxon (4,900 points)
Need explanation. I'm coding with python. Can somebody tell me what does the "grade = lambda grades:grade[1]" does? I know the "lambda" function, but i don't really understand.


It sets the variable "grade" to every string within the index 1 in the list full of tuples?

(Sorry for my english)

1 Answer

+2 votes
answered Oct 20, 2022 by Peter Minarik (82,920 points)

It doesn't do anything as the lambda expression in your code is wrong:

grade = lambda grades:grade[1]

The above line says: grade is a (lambda) function that has one argument (grades). What this function does is return the first element of grade. But grade is a function and you cannot index a function, so the expression is faulty.

Your code would make more sense to me like this (feel free to use whatever you find useful in it):

students = [("Bob", "F", 40), ("David", "F", 0)]

firstElement = lambda elements : elements[0]
grade = lambda student : student[1]

print(firstElement(students))           # ("Bob", "F", 40)
print(grade(firstElement(students)))    # F

The first lambda expression is

firstElement = lambda elements : elements[0]

, i.e., from a sequence of elements the first (0th) one is selected. If it makes more sense, you can replace element with student.

The second lambda expression is

grade = lambda student : student[1]

, i.e., from the student object (name, grade, score) we select the grade (the 1st -- zero based -- entry).

You can see in the example that you can combine these: you can select the first student then select the grade of the student:

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