global variable in main not getting recognised in another function in python

问题:

code below 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 a global variable ui, declared in main, is not recognised in another function.

Error code on running is :
Traceback (most recent call last):
File "./yamlUrwidUIPhase6.py", line 97, in <module>
main() File "./yamlUrwidUIPhase6.py", line 90, in main
form = FormDisplay() File "./yamlUrwidUIPhase6.py", line 23, in __init__
palette = ui.register_palette([
NameError: global name 'ui' is not defined

The code :

import sys   sys.path.append('./lib')   import os   from pprint import pprint   import random   import urwid   global ui  class FormDisplay(object):      def __init__(self):         self.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()         self.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 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))     return  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 main():     form = FormDisplay()     form.main()  ######################################## ##### MAIN ENTRY POINT ######################################## if __name__ == '__main__':     main() 

I don't want to change the function formLayout as I intend to add more to this basic code framework, where in another function will be added that repeatedly calls formLayout to keep updating the screen based on reading values from a yml file.

回答1:

Writing global ui in main does nothing except make it so that main itself can write to a global variable called ui. If you want to write to that global variable from other functions (like your __init__), you need to include a global declaration there too. Every function where you want to assign to a global variable has to have its own global declaration.

回答2:

okay, thanks to people for various suggestions that helped me learn about the global scoping. I followed the answer by Jeff Shannon here : Using global variables in a function other than the one that created them seem to be able to get rid of the name scoping error caused by using global ui. here is what i did i used ui=urwid.raw_display.Screen() right after the imports and then declared global ui in the functions that used it. But now I get a different kind of error. Think it best to start a new question with the error now obtained.

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