如何改进此 Python 代码以提高效率？

Question

我刚刚开始学习 Python（我第一次涉足编码），这是我第一次发帖......我希望我不会通过问这个问题来滥用论坛（我基本上是在请专家帮我学习）。如果社区对此不赞成，请告诉我。

对于密歇根公开课程的这项作业，我被指示要求用户输入，直到用户输入“完成”，此时代码应计算最大、最小、总和和平均值。在我所有的测试运行中，它运行良好。但我觉得可能有一种更简单的方法来编写这段代码。谁能提供改进建议？

largest = None
smallest = None
count = 0
sum = 0
while True:
    try:
        num = raw_input("Enter a number: ")
        if num == "done" : break
        num = float(num)
        count = count + 1
        sum = sum + num
        avg = sum/count
        if largest is None:
            largest = num
        if smallest is None:
            smallest = num
        if num < smallest:
            smallest = num
        elif num > largest:
            largest = num
        continue
    except: print 'Invalid input'

print "Maximum is", int(largest)
print "Minimum is", int(smallest)
print "Count:", int(count)
print "Sum:", int(sum)
print "Average:", avg

Answer 1

这里有几件事：

• 您可以删除continue 语句，因为它是循环的结尾；
• 您可以将if 语句压缩成if largest is None or num > largest: 这将短路并使循环变小；
• 你可以用x += y代替x = x + y；和
• 您不必计算循环内的平均值；循环结束时计算一次就足够了。

所以：

largest = None
smallest = None
count = 0
sum = 0
while True:
    try:
        num = raw_input("Enter a number: ")
        if num == "done" : break
        num = float(num)
        count += 1
        sum += num
        if largest is None or num > largest:
            largest = num
        if smallest is None or num < smallest:
            smallest = num
    except: print 'Invalid input'

print "Maximum is", int(largest)
print "Minimum is", int(smallest)
print "Count:", int(count)
print "Sum:", int(sum)
print "Average:", sum/count

但就big oh而言，你并不能提高多少：计算总和等只需要O(n)，而且还需要花费O( n) 无论如何都要读取输入。

还有一些软件工程建议：不要使用笼统的异常，始终指定您期望的异常：

largest = None
smallest = None
count = 0
sum = 0
while True:
    try:
        num = raw_input("Enter a number: ")
        if num == "done" : break
        num = float(num)
        count += 1
        sum += num
        if largest is None or num > largest:
            largest = num
        if smallest is None or num < smallest:
            smallest = num
    except ValueError: print 'Invalid input'

print "Maximum is", int(largest)
print "Minimum is", int(smallest)
print "Count:", int(count)
print "Sum:", int(sum)
print "Average:", sum/count

Answer 2

实现此目的的另一种方法是将所有输入存储在一个列表中，然后使用内置函数min()、max()、len() 和sum() 来查找值：

num=raw_input("Enter a number: ")
nums=[]
while num!="done":       #check if user has finished entering inputs
    try:
        nums.append(int(num))       #append the input as an integer to a list
        num=raw_input("Enter a number: ")   #get another input
    except ValueError:
        print "Invalid input"

print "Maximum is",max(nums)
print "Minimum is",min(nums)
print "Count:",len(nums)
print "Sum: ",sum(nums)
print "Average: ",sum(nums)/len(nums)

输出：

Enter a number: 1
Enter a number: 2
Enter a number: 3
Enter a number: 4
Enter a number: 5
Enter a number: 6
Enter a number: done
Maximum is 6
Minimum is 1
Count: 6
Sum:  21
Average:  3.5