'float' object has no attribute 'getitem' Python error

Question

When I run the code

import numpy as np
from scipy.integrate import odeint
import matplotlib.pyplot as plt

# Initial conditions

def f_func(eta,y_in):
    y_out = np.zeros(3)
    y_out[0] = y_in[1]
    y_out[1] = y_in[2]
    y_out[2] = -y_in[0]*y_in[2]/2
    return y_out

eta = np.linspace(0,8,100)
X0 = [0,0,0.33206]
X = odeint(f_func,X0,eta)

I get the error

 'float' object has no attribute '__getitem__'

When I run the following MATLAB program, everything works OK. The MATLAB function ode45 is equivalent to Pythons' odeint.

main program:

clear

global beta
beta = 1;

initial_value = [0,0,1.2322];
eta = linspace(0,4,100)
[x_out, y_out] = ode45(@falkner_skan,eta,initial_value);

plot(x_out,y_out(:,2))

falkner_skan function:

function y_out = falkner_skan(x,y_in)

global beta

y_out(1,1) = y_in(2);
y_out(2,1) = y_in(3);
y_out(3,1) = -y_in(1)*y_in(3) - beta*(1-y_in(2)^2);

end

This and this and this thread does not seem to give me any guidance.

The index operator [] calls get item. Floats do not support indexing. You are trying to do something like 1.2[3] You are probably calling f_func with a float in y_in — dawg
– dawg, Commented Sep 20, 2014 at 15:11

Mattias Farnemyhr · Accepted Answer · 2014-09-20 20:16:04Z

4

It seems as though y_in is not a list but a float value. The error rises because you're trying to get an item with obj[x] of an object which doesn't support it.

Looking at the documentation for odeint it says that the input function should take two arguments, the first being your data object and the second should be a float. Your implementation of f_func is therefore wrong.

edited Sep 20, 2014 at 20:16

answered Sep 20, 2014 at 15:08

Mattias Farnemyhr

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9 Comments

Jonny Over a year ago

I updated the question with the remainder of the code. 'y_in' has not yet been defined and this is not necessary for the use of the 'odeint' function

Mattias Farnemyhr Over a year ago

@JackTaylor Ran your code and added a print statement in the f_func function. y_in is indeed a float and not an int.

Mattias Farnemyhr Over a year ago

callable(y, t0, ...) Computes the derivative of y at t0. << This is what the documentation says about how func should be defined. y and t are both floats.

Jonny Over a year ago

Thank you @materik . what might a solution be?

Mattias Farnemyhr Over a year ago

I'm not sure of the mathematics you want to perform on the object but try using the argument that you have named eta instead of y_in. eta is an array.

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Stav Bodik · Accepted Answer · 2017-11-30 17:33:27Z

1

NumPy has float 64 object which has item() function, np.float64(10.5).item()

answered Nov 30, 2017 at 17:33

Stav Bodik

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Marjan Radfar · Accepted Answer · 2019-05-08 18:07:46Z

0

I had the same issue. According to documentation for odeint, in f_func(eta,y_in), change the order of eta and y_in, i.e. write it as f_func(y_in, eta) or set the argument tfirst to be True.

answered May 8, 2019 at 18:07

Marjan Radfar

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