The module in Example 15-2 implements a shared, system-wide namespace that collects resources used in most modules in the system, and defines global objects that span files. This allows other files to avoid redundantly repeating common imports, and encapsulates the locations of package imports; it is the only file that must be updated if paths change in the future. Using globals can make programs harder to understand in general (the source of some names is not as clear), but it is reasonable if all such names are collected in a single expected module such as this one (because there is only one place to search for unknown names).

Example 15-2. PP3E\Internet\Email\PyMailGui\SharedNames.py

################################################################ # objects shared by all window classes and main file: program-wide globals ###############################################################

# used in all window, icon titles
appname = 'PyMailGUI 2.1'

# used for list save, open, delete; also for sent messages file
saveMailSeparator = 'PyMailGUI' + ('-'*60) + 'PyMailGUI\n'

# currently viewed mail save files; also for sent-mail file
openSaveFiles     = {}           # 1 window per file,{name:win}

# standard library services
import sys, os, email, webbrowser
from Tkinter       import *
from tkFileDialog  import SaveAs, Open, Directory
from tkMessageBox  import showinfo, showerror, askyesno

# reuse book examples
from PP3E.Gui.Tools  import windows     # window border, exit protocols
from PP3E.Gui.Tools  import threadtools # thread callback queue checker

from PP3E.Internet.Email import mailtools	# load,send,parse,build utilities
from PP3E.Gui.TextEditor import textEditor	# component and pop up
# modules defined here
import mailconfig	# user params: servers, fonts, etc.
import popuputil	# help, busy, passwd pop-up windows
import wraplines	# wrap long message lines
import messagecache	# remember already loaded mail
import PyMailGuiHelp	# user documentation

def printStack(exc_info):
    # debugging: show exception and stack traceback on stdout
    print exc_info[0]
    print exc_info[1]
    import traceback
    traceback.print_tb(exc_info[2], file=sys.stdout)

# thread busy counters for threads run by this GUI
# sendingBusy shared by all send windows, used by main window quit

loadingHdrsBusy = threadtools.ThreadCounter()   # only 1
deletingBusy    = threadtools.ThreadCounter()   # only 1
loadingMsgsBusy = threadtools.ThreadCounter()   # poss many
sendingBusy     = threadtools.ThreadCounter()   # poss many