main function call fails in python

Question

I wrote the following code that creates a layout and displays some text in the layout. Next the layout is displayed on the console screen using raw display module from urwid library. However running the code fails as it doesn't find the function main that I wrote separately in a class.

Error code on running is :

Traceback (most recent call last):  
  File "./yamlUrwidUIPhase5.py", line 89, in <module>
    main()  
  File "./yamlUrwidUIPhase5.py", line 83, in main
    FormDisplay().main()  
AttributeError: 'NoneType' object has no attribute 'main'

The code :

import sys  
sys.path.append('./lib')  
import os  
from pprint import pprint  
import random  
import urwid  

def formLayout():
    text1 = urwid.Text("Urwid 3DS Application program - F8 exits.")
    text2 = urwid.Text("One mission accomplished")

    textH = urwid.Text("topmost Pile text")
    cols = urwid.Columns([text1,text2])
    pile = urwid.Pile([textH,cols])
    fill = urwid.Filler(pile)

    textT  = urwid.Text("Display") 

    textSH = urwid.Text("Pile text in Frame")
    textF = urwid.Text("Good progress !")

    frame = urwid.Frame(fill,header=urwid.Pile([textT,textSH]),footer=textF)
    dim = ui.get_cols_rows()

    ui.draw_screen(dim, frame.render(dim, True))  

def RandomColor():
    '''Pick a random color for the main menu text'''
    listOfColors = ['dark red', 'dark green', 'brown', 'dark blue',
                    'dark magenta', 'dark cyan', 'light gray',
                    'dark gray', 'light red', 'light green', 'yellow',
                    'light blue', 'light magenta', 'light cyan', 'default']
    color = listOfColors[random.randint(0, 14)]
    return color

def FormDisplay():
    import urwid.raw_display
    ui = urwid.raw_display.Screen()
    palette = ui.register_palette([
            ('Field', 'dark green, bold', 'black'), # information fields, Search: etc.
            ('Info', 'dark green', 'black'), # information in fields
            ('Bg', 'black', 'black'), # screen background
            ('InfoFooterText', 'white', 'dark blue'), # footer text
            ('InfoFooterHotkey', 'dark cyan, bold', 'dark blue'), # hotkeys in footer text
            ('InfoFooter', 'black', 'dark blue'),  # footer background
            ('InfoHeaderText', 'white, bold', 'dark blue'), # header text
            ('InfoHeader', 'black', 'dark blue'), # header background
            ('BigText', RandomColor(), 'black'), # main menu banner text
            ('GeneralInfo', 'brown', 'black'), # main menu text
            ('LastModifiedField', 'dark cyan, bold', 'black'), # Last modified:
            ('LastModifiedDate', 'dark cyan', 'black'), # info in Last modified:
            ('PopupMessageText', 'black', 'dark cyan'), # popup message text
            ('PopupMessageBg', 'black', 'dark cyan'), # popup message background
            ('SearchBoxHeaderText', 'light gray, bold', 'dark cyan'), # field names in the search box
            ('SearchBoxHeaderBg', 'black', 'dark cyan'), # field name background in the search box
            ('OnFocusBg', 'white', 'dark magenta') # background when a widget is focused
           ])
urwid.set_encoding('utf8')

def main(self):
    #self.view = ui.run_wrapper(formLayout)
    self.view = formLayout()
    ui.start()
    self.loop = urwid.MainLoop(self.view, self.palette, unhandled_input=self.unhandled_input)
    self.loop.run()

def unhandled_input(self, key):
    if key == 'f8':
        quit()
        return
def main():
    global ui

    FormDisplay().main()

########################################
##### MAIN ENTRY POINT
########################################
if __name__ == '__main__':
    main()

Answer 1

FormDisplay in your code is not a class but a function, something like this would be more appropriate. Btw, I'd recommend reading up on some of this doc http://docs.python.org/2/tutorial/classes.html

import urwid.raw_display

class FormDisplay(object):

    def __init__(self):
        self.ui = urwid.raw_display.Screen()
        self.palette = ui.register_palette([
        ('Field', 'dark green, bold', 'black'), # information fields, Search: etc.
        ('Info', 'dark green', 'black'), # information in fields
        ('Bg', 'black', 'black'), # screen background
        ('InfoFooterText', 'white', 'dark blue'), # footer text
        ('InfoFooterHotkey', 'dark cyan, bold', 'dark blue'), # hotkeys in footer text
        ('InfoFooter', 'black', 'dark blue'),  # footer background
        ('InfoHeaderText', 'white, bold', 'dark blue'), # header text
        ('InfoHeader', 'black', 'dark blue'), # header background
        ('BigText', RandomColor(), 'black'), # main menu banner text
        ('GeneralInfo', 'brown', 'black'), # main menu text
        ('LastModifiedField', 'dark cyan, bold', 'black'), # Last modified:
        ('LastModifiedDate', 'dark cyan', 'black'), # info in Last modified:
        ('PopupMessageText', 'black', 'dark cyan'), # popup message text
        ('PopupMessageBg', 'black', 'dark cyan'), # popup message background
        ('SearchBoxHeaderText', 'light gray, bold', 'dark cyan'), # field names in the search box
        ('SearchBoxHeaderBg', 'black', 'dark cyan'), # field name background in the search box
        ('OnFocusBg', 'white', 'dark magenta') # background when a widget is focused
       ])

    def main(self):
        #self.view = ui.run_wrapper(formLayout)
        self.view = formLayout()
        self.ui.start()
        self.loop = urwid.MainLoop(self.view, self.palette,   unhandled_input=self.unhandled_input)
        self.loop.run()

if __name__ == "__main__":
    form = FormDisplay()
    form.main()

Answer 2

I don't see any separate class. But according to your code, FormDisplay is a function that return nothing. FormDisplay().main() equals None.main().