CODEWITHSUNDEEP
python
Dipole
Dipole

Reputation: 1910

Passing a class instance method to another function in Python (2.7)

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.

Upvotes: 1

Views: 1590

Answers (2)

rickcnagy
rickcnagy

Reputation: 1824

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 (e.g. 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))

Upvotes: 3

Germano
Germano

Reputation: 2482

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.

Upvotes: 2

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