Python 3.x 我需要帮助理解Python代码的一部分

我已经找到了与回答在列表中查找前两个值相关的当前代码，但是，我在理解部分代码时遇到困难，在其他地方找不到任何帮助。我想知道是否有人能告诉我每个部分是什么意思

numbers = [20,67,3,2.6,7,74,2.8,90.8,52.8,4,3,2,5,7]
if numbers[0]>numbers[1]:
    m, m2 = numbers[0], numbers[1]
else:
    m, m2 = numbers[1], numbers[0]
for x in numbers[1:]:
    if x>m2:
        if x>m:
            m2, m = m, x # I am especially unsure of what is going on here
        else:
            m2 = x

---

m2返回74

下面是一个粗略的伪代码，说明它在做什么：

m将跟踪列表中最大的变量，m2将跟踪第二大变量

最初，m和m2将只是列表中的前两个元素，m将是前两个元素中较大的元素，而m2将是前两个元素中较小的元素

然后从索引1开始迭代列表，对于每个元素x，首先检查它是否大于当前m2。如果是，则需要更新m2，因为它不再是第二大元素。您还需要检查x是否大于m（这应该是列表中最大的元素），如果是，则将m更新为x，将m2更新为m之前的值

我对下面的代码进行了注释，并给出了解释：

numbers = [20,67,3,2.6,7,74,2.8,90.8,52.8,4,3,2,5,7]   # list
# This part sets m1 and m2 to be the bigger of the first two elements in the list. 
# The notation m,m2 = numbers[0], numbers[1] is equivalent to m = numbers[0] followed by m2 = numbers[1]
if numbers[0]>numbers[1]:      
    m, m2 = numbers[0], numbers[1]
else:
    m, m2 = numbers[1], numbers[0]
for x in numbers[1:]:         # iterate over list start at index 1
    if x>m2:                  # if current element is greater than m2, we need to update m2
        if x>m:               # if current element is also greater than m, we need to set m2 to the value of m, and then update m to the new largest value which is x.
            m2, m = m, x      # This is doing m2 = m followed by m = x
        else:
            m2 = x            # if current element is greater than m2 but not m, just update m2 to x

sorted(numbers, reverse=True)                 # => returns sorted version of numbers [90.8, 74, 67, 52.8, 20, 7, 7, 5, 4, 3, 3, 2.8, 2.6, 2]
sorted(numbers, reverse=True)[:2]             # => splices the list to the first two elmems i.e [90.8, 74]
m, m2 = sorted(numbers, reverse=True)[:2]     # => Does the confusing multiple assignment as m = first element of the list and m2 = second element of the list

上面的代码很好，而且非常明确，如果您是从Python开始的话，这也很好。还有一个单行程序可以为您做到这一点：

m, m2 = sorted(numbers, reverse=True)[:2]

说明：

numbers = [20,67,3,2.6,7,74,2.8,90.8,52.8,4,3,2,5,7]   # list
# This part sets m1 and m2 to be the bigger of the first two elements in the list. 
# The notation m,m2 = numbers[0], numbers[1] is equivalent to m = numbers[0] followed by m2 = numbers[1]
if numbers[0]>numbers[1]:      
    m, m2 = numbers[0], numbers[1]
else:
    m, m2 = numbers[1], numbers[0]
for x in numbers[1:]:         # iterate over list start at index 1
    if x>m2:                  # if current element is greater than m2, we need to update m2
        if x>m:               # if current element is also greater than m, we need to set m2 to the value of m, and then update m to the new largest value which is x.
            m2, m = m, x      # This is doing m2 = m followed by m = x
        else:
            m2 = x            # if current element is greater than m2 but not m, just update m2 to x

sorted(numbers, reverse=True)                 # => returns sorted version of numbers [90.8, 74, 67, 52.8, 20, 7, 7, 5, 4, 3, 3, 2.8, 2.6, 2]
sorted(numbers, reverse=True)[:2]             # => splices the list to the first two elmems i.e [90.8, 74]
m, m2 = sorted(numbers, reverse=True)[:2]     # => Does the confusing multiple assignment as m = first element of the list and m2 = second element of the list

---

不确定这个问题是否与主题有关，因此我只是发表评论

m2，m=m，x

相当于

m2=m

和

m=x

。代码应在

m

中返回列表中的最大数字，在

m2

中返回第二大数字。由于第一个

if-else

，假定至少存在两个元素。它被称为并行赋值。想象一下（m2，m）=（m，x）。虽然它很简洁（而且可以说很漂亮），但像

m2，m=m，x

这样的并行赋值（以及变量的重新声明）必然会引起混淆。非常感谢你帮助我理解它！我对开始有一个透彻的了解，就在它开始使用m2，m=m，x的时候，我不确定代码在做什么，因为我没有看到m=m以这种方式使用！谢谢，我也想过使用排序，这将是我提出的解决方案，但我看到了这个解决方案，并认为嘿，让我们尝试并理解这一点！