Question

I am turning some piece of Python code into OO-code. I define a class and a two arguments constructor.

class myclass:
     MAX=5000
     FTOL = 10**(-10)
     TINY = 10**(-10)
     def __init__(self, initPt_,fun_):
         self.initPt = initPt_
         self.fun = fun_

With this code, I expect initPt and fun to be class members. I execute the code and write this instanciation in shell:

x=myclass([1,1],Optim.fun1)

where fun1 is a function defined in module Optim, that I accurately imported.

I added to myclass a function:

def build(self):
    self.initPt=self.initPt.append(self.fun(self.initPt))
    s=[self.initPt]
    for k in range(len(self.initPt)):
        temp=[x for x in self.initPt]
        temp[k]=self.initPt[k]+1
        s.append(temp)
    return s  

I call method build on the instance x I just created. This error appears:

for k in range(len(self.initPt)):
TypeError: object of type 'NoneType' has no len()

and indeed, if I add this test line in code:

print str(type(self.iniPt))

shell indicates that type is NoneType, althought I instanciated x with self.initPt = [1,1].

Moreover, if I write x.initPt in shell, result is accurate: [1,1,0.2] (after call of method build, third value is added to initial list [1,1]).

I don’t understand why it is not resolving type dynamically. It is not object programming then. What should I do?

Thanks and regards.

Answer 1

This is at least part of your problem:

self.initPt=self.initPt.append(self.fun(self.initPt))

Using the append method of a list modifies the list in place and returns None. So this replaces the list assigned to self.initPt with None. Just do this:

self.initPt.append(self.fun(self.initPt))