CODEWITHSUNDEEP
pythonclass
m3.b
m3.b

Reputation: 667

Attribute Error creating Classes with Python

I'm new to creating classes and try to solve a problem/exercise.

When I try to instantiate the toolbox, I try to add some tools to it. My approach is to create it as a list, and append new elements to it. It returns a "None" type attribute, and I don't know how to fix it.

class Toolbox:
    def __init__(self):
        self.toolbox = []
    def add_tool(self, tool):
        self.toolbox.append(tool)
    def remove_tool(self, tool):
        self.toolbox.remove(tool)

class Hammers:
    color = ""
    def __init__(self, color=''):
        pass
    def hammer_in(self, nail):
        pass
    def remove(self, nail):
        pass
    def paint(self, color):
        pass

class Screwdrivers:
    size = 10
    def __init__(self, size=''):
        pass
    def tighten(self, screw):
        pass
    def loosen(self, screw):
        pass



toolbox = Toolbox()
hammer = Hammers()
screwdriver = Screwdrivers()

toolbox = toolbox.add_tool(hammer)
toolbox = toolbox.add_tool(screwdriver)

Output :

Traceback (most recent call last):
  File "C:Create Classes.py", line 133, in <module>
    toolbox = toolbox.add_tool(screwdriver)
AttributeError: 'NoneType' object has no attribute 'add_tool'

I'm trying to : Instantiate a toolbox, a screwdriver, and a hammer.

Put the hammer and screwdriver in the toolbox.

Thank you,

Upvotes: 0

Views: 797

Answers (3)

esocrats
esocrats

Reputation: 198

As Arseniy says, your problem comes from reassigning toolbox to a new object:

First, a Toolbox object is assigned to the toolbox reference

toolbox = Toolbox()

Then, the result of toolbox.add_tool, which is the object None is assigned to the toolbox reference, thus toolbox now no longer points to a instantiated Toolbox object:

toolbox = toolbox.add_tool(hammer)

So, what you should do instead is simply remove the re-assignment:

toolbox.add_tool(hammer)
toolbox.add_tool(screwdriver)

And this should result in:

>>> print (toolbox.toolbox)
[<__main__.Hammers object at 0x...>, <__main__.Screwdrivers object at 0x...>]

Upvotes: 1

Daniel
Daniel

Reputation: 42758

add_tool and remove_tool return implicitly None. You should not assign this return value to toolbox.

You are using class-Attributes wrongly. color should be a instance attribute. The default value of size is wrong, since size is not a empty string.

The class Hammers represent one Hammer. Why can you paint with a hammer?

class Toolbox:
    def __init__(self):
        self.toolbox = []
    def add_tool(self, tool):
        self.toolbox.append(tool)
    def remove_tool(self, tool):
        self.toolbox.remove(tool)

class Hammer:
    def __init__(self, color=''):
        self.color = color
    def hammer_in(self, nail):
        pass
    def remove(self, nail):
        pass
    def paint(self, color):
        pass

class Screwdriver:
    def __init__(self, size=10):
        self.size = size
    def tighten(self, screw):
        pass
    def loosen(self, screw):
        pass


toolbox = Toolbox()
hammer = Hammer()
screwdriver = Screwdriver()
toolbox.add_tool(hammer)
toolbox.add_tool(screwdriver)

Upvotes: 0

Arseniy
Arseniy

Reputation: 690

add_tool return nothing (None), and you assign it to toolbox

toolbox = toolbox.add_tool(hammer)  <--- problem here 
toolbox = toolbox.add_tool(screwdriver)

So, toolbox become None and 'NoneType' object has no attribute 'add_tool'

Upvotes: 1

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