如何使一个参数的默认值依赖于另一个参数(在Python中)?

问题描述：

例如，我想要

def func(n=5.0,delta=n/10):

如果用户指定了增量，请使用它.如果不是，则使用取决于n的值.这可能吗?

If the user has specified a delta, use it. If not, use a value that depends on n. Is this possible?

答

该语言不支持这种语法.

The language doesn't support such syntax.

在这些情况下，通常的解决方法是使用不是有效输入的默认值.

The usual workaround for these situations(*) is to use a default value which is not a valid input.

def func(n=5.0, delta=None):
     if delta is None:
         delta = n/10

(*)当默认值是可变的时，也会出现类似的问题.

(*) Similar problems arise when the default value is mutable.