如何使 IF 語句更有效？

Question

我創建了一個小程序，它接受用戶輸入的“飛行規范”，並根據輸入輸出該飛行的詳細信息。 然而，它只是一堆if語句，我想知道是否有任何有用的技術來減少if語句的數量並使程序更高效。

代碼：

import time

def main():

    AMS_DESTINATION = "Schiphol, Amsterdam"
    GLA_DESTINATION = "Glasgow, Scotland"
    AMS_PRICE = 150.00
    GLA_PRICE = 80.00

    # User input [LLL 0 00 L L]
    flightSpecification = str(input("Enter Flight Specification: "))
    flightDestination = flightSpecification[0:3]

    bagCount = int(flightSpecification[4])
    baggageCost = float((bagCount - 1) * 20)

    passengerAge = int(flightSpecification[6:8])

    standardMeal = 10.00  
    vegetarianMeal = 12.00
    mealType = str(flightSpecification[9])

    seatClass = str(flightSpecification[11])

    totalFlightCost = 0
    
    if flightDestination.lower() != 'ams' and flightDestination.lower() != 'gla':
        print("Please enter a valid flight specification! [LLL 0 00 L L]")
        time.sleep(2)
        main()

    if flightDestination.lower() == 'ams':
        print(f"Destination: {AMS_DESTINATION}")  
        print(f"Flight cost: £{AMS_PRICE}")
        totalFlightCost = 150

    elif flightDestination.lower() == 'gla':
        print(f"Destination: {GLA_DESTINATION}")
        print(f"Flight cost: £{GLA_PRICE}")
        totalFlightCost = 80

    print(f"Number of bags: {bagCount}")
    print(f"Baggage Cost: £{baggageCost}")

    if passengerAge > 15:
        print("Child: False")
        
    elif passengerAge <= 15:
        print("Child: True")
        totalFlightCost = totalFlightCost / 2
        standardMeal = standardMeal - 2.50
        vegetarianMeal = vegetarianMeal - 2.50
        
    elif passengerAge < 0:
        print("Age cannot be negative")
        main()

    if mealType == 'S' and seatClass != 'F':
        totalFlightCost = totalFlightCost + standardMeal
        print("Meal: Standard")
        print(f"Meal Cost: £{standardMeal}")
        
    elif mealType == 'V' and seatClass != 'F':
        totalFlightCost = totalFlightCost + vegetarianMeal
        print("Meal: Vegetarian")
        print(f"Meal Cost: £{vegetarianMeal}")

    elif mealType == 'N':
        print("Meal: None")
        print("Meal Cost: £0")

    # THIS COULD DEFINITELY BE DONE MORE EFFICIENTLY
    if seatClass == 'F':
        if mealType == 'S':
            totalFlightCost = totalFlightCost + standardMeal
            print("Meal: Standard")
            print(f"Meal Cost: FREE")
            
        elif mealType == 'V':
            totalFlightCost = totalFlightCost + vegetarianMeal
            print("Meal: Vegetarian")
            print(f"Meal Cost: £{vegetarianMeal}")
            
        print("Seating Class: First")
        totalFlightCost = totalFlightCost * 6

    elif seatClass == 'E':
        print("Seating Class: Economy")

    print(totalFlightCost)
        
        

main()

謝謝

Answer 1

代碼

除了您問題下方的評論外，我在您提到的可以優化的部分更改了一個小東西（我還刪除了用戶輸入，因為它減慢了過程，最后您會明白）：

import time

def main2():

    AMS_DESTINATION = "Schiphol, Amsterdam"
    GLA_DESTINATION = "Glasgow, Scotland"
    AMS_PRICE = 150.00
    GLA_PRICE = 80.00

    # User input [LLL 0 00 L L]
    # flightSpecification = str(input("Enter Flight Specification: "))
    flightSpecification = 'AMS 1 22 V F'
    flightDestination = flightSpecification[0:3]

    bagCount = int(flightSpecification[4])
    baggageCost = float((bagCount - 1) * 20)

    passengerAge = int(flightSpecification[6:8])

    standardMeal = 10.00  
    vegetarianMeal = 12.00
    mealType = str(flightSpecification[9])

    seatClass = str(flightSpecification[11])

    totalFlightCost = 0
    
    if flightDestination.lower() != 'ams' and flightDestination.lower() != 'gla':
        print("Please enter a valid flight specification! [LLL 0 00 L L]")
        time.sleep(2)
        main()

    if flightDestination.lower() == 'ams':
        print(f"Destination: {AMS_DESTINATION}")  
        print(f"Flight cost: £{AMS_PRICE}")
        totalFlightCost = 150

    elif flightDestination.lower() == 'gla':
        print(f"Destination: {GLA_DESTINATION}")
        print(f"Flight cost: £{GLA_PRICE}")
        totalFlightCost = 80

    print(f"Number of bags: {bagCount}")
    print(f"Baggage Cost: £{baggageCost}")

    if passengerAge > 15:
        print("Child: False")
        
    elif passengerAge <= 15:
        print("Child: True")
        totalFlightCost = totalFlightCost / 2
        standardMeal = standardMeal - 2.50
        vegetarianMeal = vegetarianMeal - 2.50
        
    elif passengerAge < 0:
        print("Age cannot be negative")
        main()

    if mealType == 'S' and seatClass != 'F':
        totalFlightCost = totalFlightCost + standardMeal
        print("Meal: Standard")
        print(f"Meal Cost: £{standardMeal}")
        
    elif mealType == 'V' and seatClass != 'F':
        totalFlightCost = totalFlightCost + vegetarianMeal
        print("Meal: Vegetarian")
        print(f"Meal Cost: £{vegetarianMeal}")

    elif mealType == 'N':
        print("Meal: None")
        print("Meal Cost: £0")

    # THIS COULD DEFINITELY BE DONE MORE EFFICIENTLY
    if seatClass == 'F' and mealType is 'S':
        totalFlightCost = totalFlightCost + standardMeal
        print("Meal: Standard")
        print(f"Meal Cost: FREE")

        print("Seating Class: First")
        totalFlightCost = totalFlightCost * 6
            
    elif seatClass is 'F' and mealType == 'V':
        totalFlightCost = totalFlightCost + vegetarianMeal
        print("Meal: Vegetarian")
        print(f"Meal Cost: £{vegetarianMeal}")
            
        print("Seating Class: First")
        totalFlightCost = totalFlightCost * 6

    elif seatClass == 'E':
        print("Seating Class: Economy")

    print(totalFlightCost)

測試

更改 main 中的輸入，您將在下面的測試中認識到沒有真正的性能問題：

start = time.time()
main()
print('main() takes: ')
print(time.time() - start)

start = time.time()
main2()
print('main2() takes:') 
print(time.time() - start)

結果

main() 需要：7.319450378417969e-05 秒

main2() 需要：4.935264587402344e-05 秒

值得一提

在您設置的遞歸路徑中（在評論中提到），您還使用 time.sleep(2)。 插入硬編碼睡眠總是會影響你的表現。

Answer 2

對於這樣一個簡單的程序，它根本不值得考慮效率。 然而，展望未來，如果您要驗證具有數十萬或更多項目的一批數據，那么效率就會成為一個問題。

以下是一些需要考慮的要點：

# flightSpecification = str(input("Enter Flight Specification: "))
flightSpecification = input("Enter Flight Specification: ")

注意input()總是返回一個str ，所以它周圍的str()是多余的。

# mealType = str(flightSpecification[9])
mealType = flightSpecification[9]

類似地，由於flightSpecification已經是str ，因此str()是多余的。

#if flightDestination.lower() == 'ams':
flightDestinationLower = flightDestination.lower()
if flightDestinationLower == 'ams':

由於您進行了類似的比較，因此執行lower()一次可能比多次執行更有效。

flightDestinationLower = flightDestination.lower()
if flightDestinationLower == 'ams':
    print(f"Destination: {AMS_DESTINATION}")  
    print(f"Flight cost: £{AMS_PRICE}")
    totalFlightCost = 150

elif flightDestinationLower == 'gla':
    print(f"Destination: {GLA_DESTINATION}")
    print(f"Flight cost: £{GLA_PRICE}")
    totalFlightCost = 80
else:
    print("Please enter a valid flight specification! [LLL 0 00 L L]")
    time.sleep(2)
    #main()
    continue

重新排列if的順序，以便else:不需要進行比較。 也不要在您打算使用迭代的地方使用遞歸。