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Groups > comp.lang.python > #59272

Re: PyMyth: Global variables are evil... WRONG!

From Terry Reedy <tjreedy@udel.edu>
Subject Re: PyMyth: Global variables are evil... WRONG!
Date 2013-11-12 20:20 -0500
References <7b97786a-2aaf-454c-8c3a-1c19d20d4345@googlegroups.com> <deh8la-8p4.ln1@ozzie.tundraware.com> <82561733-d131-45de-ab10-c847f1960dc4@googlegroups.com>
Newsgroups comp.lang.python
Message-ID <mailman.2517.1384305627.18130.python-list@python.org> (permalink)

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On 11/11/2013 11:46 PM, Rick Johnson wrote:

> No, Python modules can be poked, prodded, and violated by
> any pervert who can spell the word "import".

Or by clever programmers.

> Attribute values can be reassigned and state can be
> externally manipulated

Perhaps for good reasons.

> resulting in all types of undefined behaviors

Not necessarily. Manipulation can also eliminate undefined behaviors.

Suppose I want to test a Idle function that uses a tkinter.messagebox 
class to communicate with users. Perhaps the module has

from tkinter.messagebox import askretrycancel

The behavior of askretrycancel(*args) is undefined insofar as it depends 
on the arbitrary actions of a human user (it may even hang forever). In 
an automated test, there is no user, and it is difficult to simulate the 
eyes and fingers of one while leaving askretrycancel as it is. 
Monkeypatching with a mock solves this. Simplifying a bit, and leaving 
out details, I have done something like this.

from mock_tkinter import mbox  # mocks all messageboxes
mock_arc = mbox()
import mod
mod.askretrycancel = mock_arc

This makes mod.askretrycancel deterministic in that I can preload a 
response into mock_arc before calling the function or method in mod. 
(This simulates a user's fingers.) The mock also saves the values sent 
to it to see if they are what they should be. (This simulates a user's 
eyes.)

-- 
Terry Jan Reedy

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Thread

PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-11 18:06 -0800
  Re: PyMyth: Global variables are evil... WRONG! Tim Daneliuk <tundra@tundraware.com> - 2013-11-11 20:47 -0600
    Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-11 20:46 -0800
      Re: PyMyth: Global variables are evil... WRONG! Chris Angelico <rosuav@gmail.com> - 2013-11-12 16:02 +1100
      Re: PyMyth: Global variables are evil... WRONG! Ricardo Aráoz <ricaraoz@gmail.com> - 2013-11-12 07:15 -0300
      Re: PyMyth: Global variables are evil... WRONG! Tim Chase <python.list@tim.thechases.com> - 2013-11-12 05:32 -0600
      Re: PyMyth: Global variables are evil... WRONG! Terry Reedy <tjreedy@udel.edu> - 2013-11-12 20:20 -0500
      Re: PyMyth: Global variables are evil... WRONG! Tim Daneliuk <tundra@tundraware.com> - 2013-11-13 18:17 -0600
        Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-13 18:25 -0800
  Re: PyMyth: Global variables are evil... WRONG! jongiddy <jongiddy@gmail.com> - 2013-11-12 06:12 -0800
    Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-12 07:05 -0800
      Re: PyMyth: Global variables are evil... WRONG! jongiddy <jongiddy@gmail.com> - 2013-11-12 07:33 -0800
        Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-12 09:00 -0800
          Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-12 09:42 -0800
          Re: PyMyth: Global variables are evil... WRONG! Tim Chase <python.list@tim.thechases.com> - 2013-11-12 11:45 -0600
          Re: PyMyth: Global variables are evil... WRONG! jongiddy <jongiddy@gmail.com> - 2013-11-12 14:41 -0800
            Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-12 18:45 -0800
              Re: PyMyth: Global variables are evil... WRONG! Tim Chase <python.list@tim.thechases.com> - 2013-11-12 21:22 -0600
              Re: PyMyth: Global variables are evil... WRONG! Andrew Cooper <root@127.0.0.1> - 2013-11-13 22:00 +0000
                Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-13 18:16 -0800
  Re: PyMyth: Global variables are evil... WRONG! Alister <alister.ware@ntlworld.com> - 2013-11-12 14:32 +0000
    Re: PyMyth: Global variables are evil... WRONG! Chris Angelico <rosuav@gmail.com> - 2013-11-13 02:22 +1100
  Re: PyMyth: Global variables are evil... WRONG! "Rhodri James" <rhodri@wildebst.demon.co.uk> - 2013-11-13 23:42 +0000
    Re: PyMyth: Global variables are evil... WRONG! Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-11-13 23:57 +0000
    Re: PyMyth: Global variables are evil... WRONG! Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-11-14 01:09 +0000
      Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-13 19:22 -0800
        Re: PyMyth: Global variables are evil... WRONG! Chris Angelico <rosuav@gmail.com> - 2013-11-14 14:29 +1100
          Re: PyMyth: Global variables are evil... WRONG! Roy Smith <roy@panix.com> - 2013-11-13 23:33 -0500
            Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-13 20:40 -0800
            Re: PyMyth: Global variables are evil... WRONG! Chris Angelico <rosuav@gmail.com> - 2013-11-14 15:53 +1100
            Re: PyMyth: Global variables are evil... WRONG! Steven D'Aprano <steve@pearwood.info> - 2013-11-14 06:25 +0000
          Re: PyMyth: Global variables are evil... WRONG! unknown <unknown@unknown.com> - 2013-11-14 09:41 +0000
    Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-13 18:10 -0800
      Re: PyMyth: Global variables are evil... WRONG! Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-11-14 02:45 +0000
        Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-13 19:45 -0800
          Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-13 20:01 -0800
          Re: PyMyth: Global variables are evil... WRONG! Steven D'Aprano <steve@pearwood.info> - 2013-11-14 05:50 +0000
            Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-14 09:26 -0800
              Re: PyMyth: Global variables are evil... WRONG! Joel Goldstick <joel.goldstick@gmail.com> - 2013-11-14 12:37 -0500
              Re: PyMyth: Global variables are evil... WRONG! Ethan Furman <ethan@stoneleaf.us> - 2013-11-14 09:56 -0800
                Re: PyMyth: Global variables are evil... WRONG! Alister <alister.ware@ntlworld.com> - 2013-11-14 20:12 +0000
                Re: PyMyth: Global variables are evil... WRONG! Chris Angelico <rosuav@gmail.com> - 2013-11-15 09:43 +1100
              Re: PyMyth: Global variables are evil... WRONG! Joel Goldstick <joel.goldstick@gmail.com> - 2013-11-14 13:43 -0500
              Re: PyMyth: Global variables are evil... WRONG! Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-11-14 19:04 +0000
              Re: PyMyth: Global variables are evil... WRONG! Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-11-15 08:19 +0000
                Re: PyMyth: Global variables are evil... WRONG! Tim Daneliuk <tundra@tundraware.com> - 2013-11-15 09:26 -0600
                Re: PyMyth: Global variables are evil... WRONG! Chris Angelico <rosuav@gmail.com> - 2013-11-16 02:42 +1100
                Re: PyMyth: Global variables are evil... WRONG! Tim Daneliuk <tundra@tundraware.com> - 2013-11-15 17:33 -0600
                Re: PyMyth: Global variables are evil... WRONG! Tim Daneliuk <tundra@tundraware.com> - 2013-11-15 17:33 -0600
                Re: PyMyth: Global variables are evil... WRONG! Rick Johnson <rantingrickjohnson@gmail.com> - 2013-11-15 20:01 -0800
                Re: PyMyth: Global variables are evil... WRONG! Chris Angelico <rosuav@gmail.com> - 2013-11-16 15:19 +1100
                Re: PyMyth: Global variables are evil... WRONG! Chris Angelico <rosuav@gmail.com> - 2013-11-16 15:14 +1100

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