Python没有switch...case语法，如何优雅的避免if..elif...elif...else...

例如我们要把如下的一段代码给转换为非if…elif…elif…else…的代码结构

def convert_grade(scr):
    if scr >= 90:
        print('A')
    elif scr >= 80:
        print('B')
    elif scr >= 70:
        print('C')
    elif scr >= 60:
        print('D')
    else:
        print('F')


convert_grade(89)

方法一，利用列表

base_list = [(90, 'A'), (80, 'B'), (70, 'C'), (60, 'D')]


def convert_grade(scr):
    for _scr, grade in base_list:
        if scr >= _scr:
            print(grade)
            break
    else:
        print('F')


convert_grade(59)

方法二，利用bisect模块

from bisect import bisect
#该模块中的bisect主要采用二分查找的算法，时间复杂度为 O(logn)。

def convert_grade(scr, breakpoints=[60, 70, 80, 90], grades='FDCBA'):
    i = bisect(breakpoints, scr)#返回等级值所在的索引值，breakpoints数字可以乱序
    return grades[i]


print([convert_grade(score) for score in [33, 99, 77, 70, 89, 90, 100]])

方法三，使用字典

grades = {
    
    "A": 90, "B": 80, "C": 70, "D": 60}


def convert_grade(scr):
    for grade, _src in sorted(grades.items()):  # 3.6以下的版本grades的顺序会变，所以我们对它排序
        if scr >= _src:
            return grade
    return "F"


print(convert_grade(45))

def convert_grade(score):
    """Return a letter grade."""
    grades = {
    
    100: "A", 90: "A", 80: "B", 70: "C", 60: "D"}
    return grades.get((score // 10) * 10, "F")
print([grade(scr) for scr in [100, 33, 95, 61, 77, 90, 89]])

方法四，使用zip(),next()

def convert_grade(scr):
    grades = zip('ABCD', (90, 80, 70, 60))
    return next((grade for grade, limit in grades if scr >= limit), 'F')


print(convert_grade(40))

方法五，利用math模块

from math import floor


def grade(mark):
    return ["D", "C", "B", "A"][min(int(floor(mark / 10)) - 6, 3)] if mark >= 60 else "F"


print(grade(79))

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