Python min和max内置模块混淆

Question

I am supposed to write a function name shortest() that finds the length of the shortest string in a list of strings.

The function shortest() takes one parameter: 1. a list of strings, textList

The function shortest() should return the length of the shortest string in text List. You may assume that textList contains at least one element (string).

For example, the following would be correct output:

>>> beatleLine = ['I', 'am', 'the', 'walrus']
>>> print(shortest(beatleLine))
1

--

When I finished writing the shortest() function, I came up with this solution

def shortest(textList):
    return len(max(textList))

string = ['Hey', 'Hello', 'Hi']
print(shortest(string))

But I am confused as to why the max function returns the length of the shortest function instead of the min function.

If I change max to min, the largest value is returned. It almost seems as if min and max are switched.

I am using Python 3.4 and running it on IDLE.

Answer 1

max returns the largest item in an iterable. Since you didn't provide any key function to compare who is the largest it'll return the biggest element in lexicographical order:

>>> max(['I', 'am', 'the', 'x', 'walrus'])
'x'

You need to tell max to which key function it will use to compare elements for deciding who is the largest :

>>> max(['I', 'am', 'the', 'walrus', 'x'], key=len)
'walrus'

That being said:

>>> def shortest(textList):
...     return len(min(textList, key=len))

Alternatives using list comprehensions or map :

>>> min(len(text) for text in textList)

--

>>> min(map(len, textList))

Answer 2

If you compare the strings themselves as the function does (ie sort the list and display it), you'll see that they order them a specific way that gives the results you see.

You want to use the key argument to pass a function that will give the length of the item instead of using the item itself.