[Python] Get the second largest number in a list in linear time

I'm obtaining the second largest number from a list:

>>> numbers = [20,67,3,2.6,7,74,2.8,90.8,52.8,4,3,2,5,7]
>>> numbers.remove(max(numbers))
>>> max(numbers)
74


Except that the easy list processing runs through the list twice: to find the largest and then the 2nd largest. It's also destructive - I need two copies of the data if I wanted to keep the original:

>>> 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[2:]:
... if x>m2:
... if x>m:
... m2, m = m, x
... else:
... m2 = x
...
>>> m2
74


Which runs through the list just once, but isn't terse and clear like the previous solution.

Is there a way to have both? The clarity of the first version, but the single run through of the second?

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