计算Python的平均成绩？

Question

I am trying to get the average of two passing grades. The output should be:

• 0.0 if neither of the grades is a passing grade both <50
• The passing grade, if only one of the grades is a passing grade (if one is >50)
• The average of the two grades, if both are passing grades (if both are greater than 50)

Here is my code so far:

def passing_grade(grade1,grade2):
    '''(number, number)--> number
    This function definition prints the average of all passing grade(s)
    '''
    # Function 1 - If both numbers are outside the grading range (0-100)
    if 0.0 < grade1 > 100.0 and 0 < grade2 > 100.0:
           print ('Not available grading')

    elif 0.0 >= grade1 <= 50.0 and 0.0 >= grade2 <= 50.0:
            print (0.0)

    #Function 2 - If one of the grades is passing then, print passing grade
    elif 0.0 >= grade1 <= 50.0 and 0.0 >= grade2 >= 50.0:
        print (grade2)
    elif 0.0 >= grade1 >= 50.0 and 0.0 >= grade2 <= 50.0:
        print (grade1)

    #Function 3 - If both grades are passing >50 then print the average
    elif 50.0 > grade1 <= 100.0 and 50.0> grade2 <= 100.0:
        print ((grade1+grade2)/2)

Answer 1

I'm just guessing about your problem here, since you haven't specified, but it looks like you bad logic in the second part of "Function #2":

elif 0.0 >= grade1 <= 50.0 and 0.0 >= grade2 >= 50.0:
    print (grade2)
elif 0.0 >= grade1 >= 50.0 and 0.0 >= grade2 <= 50.0:
    print (grade1)

Should be:

elif grade1 <= 50.0 and grade2 >= 50.0:
    print (grade2)
elif grade1 >= 50.0 and grade2 <= 50.0:
    print (grade1)

If you look at your original conditions, you keep checking 0.0 >= gradeN , which means is only true if the grade is a negative number. There are similar problems in some of your other sections.

Answer 2

Your comparisons are screwed up. They don't say what you mean, and many evaluate to False always. There can be no grade1 such that 0.0 >= grade1 >= 50.0 , as there are no nonpositive numbers greater-equal 50. I suggest you write out your multiple comparisons "the long way" until you're clear about what you mean to say, rather than using this keystroke-saving feature of Python. a < b < c in Python means a < b and b < c not a < b or b < c which is the form of what you want to say in your first 'if' statement.

Finally, when writing multiple comparisons in one expression, don't mix directions of the comparisons, it's needlessly confusing (for you, to start with).

A more concise way of writing (the calculation part of) your function:

def avg_passing_grade(grade1, grade2):
    passing_grades = [g for g in (grade1, grade2) if 50 <= g <= 100]
    return sum(passing_grades)/max(1, len(passing_grades))

This makes a list passing_grades containing only the grades supplied to the function that are passing. The function returns their average, taking care not to divide by 0 in case no grades are passing.

Although the following may be overkill, it's within such easy reach that I have to mention it: the function above generalizes easily to one that takes an arbitrary number of grades:

def average_passing_grade(* grades):
    '''Return the average of the passing grades among grades.'''
    passing_grades = [g for g in grades if 50 <= g <= 100]
    return sum(passing_grades)/max(1, len(passing_grades))

which you can use like this:

>>> average_passing_grade()
0.0
>>> average_passing_grade(35.3)
0.0
>>> average_passing_grade(75.5)
75.5
>>> average_passing_grade(35.3, 88)
88.0
>>> average_passing_grade(88, 20)
88.0
>>> average_passing_grade(50, 100)
75.0
>>> average_passing_grade(40, 50, 60, 70, 80, 90)
70.0

Answer 3

Besides the bad logic pointed out in the other answers, you could use max and min to do a single logical check for certain cases.

if grade1 >= 50.0 and grade2 >= 50.0: 

can be

if min (grade1, grade2) >= 50.0: # Both are >= 50.0

similarly

if  max(grade1, grade2) < 50.0 # both are less than 50.0

Once those two have been shown false, the the else means that one is on each side of the limit.

Similarly, to test for the invalid values you can use

if max(grade1, grade2) > 100.0 or min(grade1, grade2) < 0:

means that at least one grade is invalid

if min(grade1, grade2) > 100 or max(grade1, grade2) <0:

means that both grades are invalid in the same way.

Answer 4

I am no expert in Python. However, I'm pretty sure your error is because of your if conditions.

    if 0.0 < grade1 > 100.0 and 0 < grade2 > 100.0:

Should be something like

    if (grade1 < 0 or grade1 > 100) and (grade2 < 0 or grade2 > 100):