Why is my python function not defined, when it exists in the same file?

问题

I have a simple function, which I shall call myFunction. It takes two parameters, performs some calculations on them, and returns the result.

I also have a class, MyClass, which has a constructor that has a header like this:

__init__(self, bar, fun=myFunction):

When I try to run anything in this class, I get the following error:

MyClass
    def __init__(self, bar, fun=myFunction):
NameError: name 'myFunction' is not defined

If I remove this class, I can use myFun in the Python Shell, so what's the deal?

回答1:

You haven't shown the actual code so it's hard to be sure, but I bet myFunction is defined after MyClass. The default value expression is evaluated when the __init__ method is defined, so myFunction must be defined at that point. Defining it later is too late.

回答2:

myFunction is a variable, not a value so you can't use it as a default parameter.

Maybe you could use a lambda function as the default parameter instead of the name of a declared function.

来源：https://stackoverflow.com/questions/11165423/why-is-my-python-function-not-defined-when-it-exists-in-the-same-file