arcpy - How to control state of buttons in Python Add-In?

I have bunch of buttons to perform separate tasks within a Python Add-In. Buttons are greyed out and required to be enabled after initial tools run. In the following example, tool1 is turned off after execution using its ID and button1 is enabled. Classes are arranged alphabetically at the time of Add-In construction. This configuration of classes works sometimes and fails at others with message: "NameError: global name 'button1' is not defined". This is confusing as to why it runs sometimes and fails at others. Can anyone please help with explanation as to why is it the case and how to better control the state of buttons without error?

class Calc(object):

    """Implementation for test_addin.button1 (Button)"""
    def __init__(self):
        self.enabled = False
        self.checked = False
    def onClick(self):
        """do something"""

class process(object):
    """Implementation for test_addin.tool1 (Tool)"""
    def __init__(self):

        self.enabled = True
        self.cursor = 3

    def onMouseDownMap(self, x, y, button, shift):
        """do something"""

        tool1.enabled = False
        button1.enabled = True

Answer

The state of buttons can be controlled with the answer provided here.