将类实例方法传递给Python中的另一个函数（2.7）

Question

sorry if the title does not make sense, I am relatively new to this. This is my code:

class MeanFlow:
    def __init__(self, V0=1):
        self.V0 = V0
    def LHS(self, t, y):
        return y[0]*self.V0


def velocity_field(w,f):
    z = 0 # dummy 
    u = f(z,w).real
    v = -1*f(z,w).imag 
    return u, v

w0 = 1
mean = MeanFlow()
dwdz = mean.LHS
print(velocity_field(w0, dwdz))

But I get the error TypeError: 'int' object has no attribute '__getitem__'

My question is how do I pass this function which is a method of my class instance into another function. If I define the function outside the class and pass it to another function this works but is not what I want. Thanks!

Edit: The typo return = y[0]*self.V0 has been corrected.

Answer 1

What's generating TypeError: 'int' object has no attribute '__getitem__' is this:

y[0]

This is because at this point, y 's value is 1 , an integer, and y[0] is acting as if y is a list or string ( __getitem__ is the method called to get items in lists). If y were a list (eg y = [1] ), it'd work fine.

If you remove the [0] , you're in business:

class MeanFlow:
    def __init__(self, V0=1):
        self.V0 = V0
    def LHS(self, t, y):
        return y*self.V0


def velocity_field(w,f):
    z = 0 # dummy 
    u = f(z,w).real
    v = -1*f(z,w).imag 
    return u, v

w0 = 1
mean = MeanFlow()
dwdz = mean.LHS
print(velocity_field(w0, dwdz))

Answer 2

There is an error in your code. You are passing 1 as the first argument to velocity_field which in turn passes it to LHS as the second argument ( y ). Lastly, you call __getitem__ on y by doing y[0] , and that raises the exception.

Moreover, there is a syntax error as you assign the result to return .