List comprehension with conditional function inside-CodePudding

I want to write list comprehension with conditional function inside. This what i have so far

more_grades = [0.0, 50.0, 49.9, 79.0, 101.0, 65.0, 54.2, 48.2, 78.9]
def grade_classification(grade):
        if grade < 40:
            result = 'fail'
        elif grade >= 40 and grade < 50:
            result = 'Pass'
        elif grade >= 50 and grade < 60:
            result = '2:2'
        elif grade >= 60 and grade < 70:
            result= '2:1'
        elif grade >= 70:
            result = 'First'
        else:
            result = 'unknown grade'
        return result
studen_classficatin = [result for result in more_grades if grade_classification(result)]
print(studen_classficatin)

The output should be = ['Fail', '2:2', 'Pass', 'First', 'First', '2:1', '2:2', 'Pass', 'First'] but from the code above its giving me = [0.0, 50.0, 49.9, 79.0, 101.0, 65.0, 54.2, 48.2, 78.9] I dont know what i am doing wrong. Please any suggestion?

CodePudding user response：

Change it to this instead:

studen_classficatin = [grade_classification(result) for result in more_grades]

The trailing if will determine whether or not an element should be added to the list, not "transform" the element itself

CodePudding user response：

You don't really need to do list comprehension, instead you can apply map to your list to call a function on each entry of the list. The result will be an iterator that consists of the returned value for each value in your previous list:

studen_classficatin = map(grade_classification, more_grades)

map returns an iterator, so it doesn't actually do anything until you iterate over the list. If you want to print it, call list on the iterator to exhaust it:

studen_classficatin = list(map(grade_classification, more_grades))

CodePudding user response：

Your code is this:

studen_classficatin = [result for result in more_grades if grade_classification(result)]

Which, because non-empty strings are truthy, is the same as:

studen_classficatin = [result for result in more_grades if True]

Which is the same as:

studen_classficatin = [result for result in more_grades]

which is the same as just copying more_grades.