global variables or inheritence

[Donn Cave]

Quoth Thomas Rasmussen <simpsons at kom.auc.dk>:
...
| Well i'm programming a small admin tool, which must use the users
| $EDITOR for editing files. This works fine if the EDITOR sysenv is
| set, if not, then i want to ask the user which editor he want to use,
| and then pass this variable to the module that handles
| filemanipulation. This modules is also in another file if it
| matters... I must add that this is my first real program made in
| python...

When things get difficult in Python, my reflex is to write a
big hairy class.  Maybe something like this would work, or at
least give you an idea:

  import os
  import sys

  class UserEditor:
          def __init__(self, default_editor = None):
                  self.program = default_editor
          def get(self):
                  if not self.program:
                           try:
                                    self.program = os.environ['EDITOR']
                           except KeyError:
                                    sys.stdout.write('Editor? ')
                                    ... etc.
                  return self.program
          def set(self, editor):
                  self.program = editor
          def invoke(self, file):
                  program = self.get()
                  return os.system('%s %s' % (program, file)) == 0

  editor = UserEditor()


Let's say that's at module scope in the "interfaces" module.  In other
modules you may say

  filemanipulation.xyzfile(interfaces.editor.get(), ...)

or maybe this class will turn out to be a convenient place to do some
stuff that is now cluttering up filemanipulation, so you should say

  filemanipulation.xyzfile(interfaces.editor, ...)

	Donn Cave, University Computing Services, University of Washington
	donn at u.washington.edu