python之max使用技巧

max获取最大值时，若给定的值如果为空，且未给max初始默认值，max会抛出异常

a = []
max(a)

抛出的异常

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
 in 
      1 a = []
----> 2 max(a)

ValueError: max() arg is an empty sequence

未防止max抛出异常，可指定默认值

a = []
max(a,default=False)

结果为False

False

官方说明

max(iterable, *[, key, default])
max(arg1, arg2, *args[, key])
Return the largest item in an iterable or the largest of two or more arguments.

If one positional argument is provided, it should be an iterable. The largest item in the iterable is returned. If two or more positional arguments are provided, the largest of the positional arguments is returned.

There are two optional keyword-only arguments. The key argument specifies a one-argument ordering function like that used for list.sort(). The default argument specifies an object to return if the provided iterable is empty. If the iterable is empty and default is not provided, a ValueError is raised.

If multiple items are maximal, the function returns the first one encountered. This is consistent with other sort-stability preserving tools such as sorted(iterable, key=keyfunc, reverse=True)[0] andheapq.nlargest(1, iterable, key=keyfunc).

New in version 3.4: The default keyword-only argument.