Factory Design Pattern

Question

I am trying to implement Factory Design Pattern and have done this far till now.

import abc

class Button(object):
    __metaclass__ = abc.ABCMeta

    html = ""
    def get_html(self, html):
        return self.html

class ButtonFactory():
    def create_button(self, type):
        baseclass = Button()
        targetclass = type.baseclass.capitalize()
        return targetclass

button_obj = ButtonFactory()
button = ['image', 'input', 'flash']
for b in button:
    print button_obj.create_button(b).get_html()

The output should be the HTML of all your button types.

I get the error like this

AttributeError: 'str' object has no attribute 'baseclass'

I am trying to implement a class which has different variations, such as ImageButton, InputButton and FlashButton. Depending on the place, it may need to create different html for the buttons

Answer 1

You are trying to call baseclass attribute of str, which does not exist, because b gets string values (one of ['image', 'input', 'flash']). If you want to create an object according to a string representing its name, you can use the globals() dictionary, which holds a mapping between variable names and their values.

class Button(object):
    html = ""
    def get_html(self):
        return self.html

class Image(Button):
    html = "<img></img>"

class Input(Button):
    html = "<input></input>"

class Flash(Button):
    html = "<obj></obj>"

class ButtonFactory():
    def create_button(self, typ):
        targetclass = typ.capitalize()
        return globals()[targetclass]()

button_obj = ButtonFactory()
button = ['image', 'input', 'flash']
for b in button:
    print button_obj.create_button(b).get_html()

EDIT: Using globals() or locals() is also not a good practice so, if you can, it is better to create a mapping between the relevant objects and their names, like this:

button_objects = {'image':Image,'flash':Flash,'input':Input}

and replace create_button with:

def create_button(self, typ):        
    return button_objects[typ]()

Answer 2

Here is where your error comes from:

button = ['image', 'input', 'flash'] # button contains strings

for b in button: # b is a string

create_button(b) # argument 'type' is a string

type.baseclass... # hence the AttributeError

Your list button needs to contain objects that have the baseclass attribute, not their names as strings. Also, you shouldn't use type as a variable name, as it shadows a Python standard library function type().