Python class calling other method

Question

I don't understand why this code doesn't work:

import numpy as np 
class Normalizer:
 def __init__(self,x):
 self.x = x 
 def mean(self):
 return np.sum(self.x)/np.size(self.x)
 def mean_zero(self):
 return self.x - self.x.mean()
 def new_calc(self):
 return self.x.mean_zero()
 a = np.random.randint(150,200,(5,8))
 heights = Normalizer(a)
 print(a)
 print(heights.mean()) 
 print(heights.mean_zero())
 print(heights.mean_zero().mean())
 print(heights.new_calc())

It executes heghts.mean_zero() correctly but in the method def new_calc(self) it doesn't execute it. It would be great if someone could explain that to me. Thanks!

• Jay Modi: mean_zero is class method. You can't call it with your class's variable.
• DirtyBit: Use self.mean_zero() instead of self.x.mean_zero()

Answer 1

I don't understand why this code doesn't work:

if you run the following code it will throw an error:

AttributeError: 'numpy.ndarray' object has no attribute 'mean_zero'

• locate the problem, the only place where mean_zero has been called is new_calc method. So, first step done.

• analyze, if you look at Normalize class it has one attribute x which is of the type numpy.ndarray. If you carefully read the error message it says that ndarray type doesn't have the attribute mean_zero. On the other hand you have mean_zero method defined in your class and that is the one you should call.

These two steps leads to conclusion that the problem is in new_calc method:

def new_calc(self):
 return self.mean_zero() #(wrong)return self.x.mean_zero()

Answer 2

I am not sure what x from the __init__ is but it is very likely that you actually want to call mean_zero in new_calc in the context of self variable (the same object):

def new_calc(self):
 return self.mean_zero()

Answer 3

Insted of self.x.mean_zero() write self.mean_zero()

import numpy as np 
class Normalizer:
 def __init__(self,x):
 self.x = x 
 def mean(self):
 return np.sum(self.x)/np.size(self.x)
 def mean_zero(self):
 return self.x - self.mean()
 def new_calc(self):
 return self.mean_zero()
a = np.random.randint(150,200,(5,8))
heights = Normalizer(a)
print(a)
print(heights.mean()) 
print(heights.mean_zero())
print(heights.mean_zero().mean())
print(heights.new_calc())

Answer 4

You're initializing Normalizer with 'a', which is the output of np.random.randint, which returns a numpy.ndarray object.

In the new_calc method you are attempting to call the mean_zero method of the ndarray object, but ndarray has no such method. mean_zero is a method on Normalizer, but self.x is not of type Normalizer.

I'm not sure what this code new_calc is supposed to do. If you can make that clearer, I may be able to provide more assistance.

• Magnus Hoglund: new_calc was just a simplification to debug what I am actually trying to accomplish. The actual code will look like this: def variance(self): return (np.sum((self.x.mean_zero()**2)))/ np.size(self.x)

Answer 5

The culprit:

def new_calc(self):
 return self.x.mean_zero()

The reason:

self.x is an attribute of the Normalizer class. So if heights is an instance of the Normalizer class, then heights.x is the self.x.

The answer:

def new_calc(self):
 return self.mean_zero()

The justification:

AttributeError: 'numpy.ndarray' object has no attribute 'mean_zero'

ndarray has no such method. mean_zero is a method of Normalizer